Theorie-Seminar

David Blaschke (Uni Wroclaw)
Twin stars and the QCD phase diagram

It has been suggested that the observation of pulsars with the same mass but significantly different radii (twin stars) would prove that the existence of a critical endpoint in the QCD phase diagram since this phenomenon requires a strong phase transition in cold neutron star matter. We explore whether such a phase transition in neutron star cores, possibly coupled with a secondary kick mechanism such as neutrino or electromagnetic rocket effect, may provide a formation path for isolated and eccentric millisecond pulsars (MSPs). We show that a gravitational mass loss of approximately 0.01 solar masses suffices to produce an eccentricity of the order of 0.1 without the need of a secondary kick mechanism. We also show that in warm supernova and merger matter, thermal twin stars can be formed, even when the mass-radius diagram of cold neutron stars has no twins. We speculate about a correlation of the thermal twin phenomenon with the supernova explodability of massive blue supergiant stars and discuss the accessibility of color superconducting quark matter phases in heavy-ion collisions.

Theorie-Seminar

Patrick Cook (MSU)
Parametric Matrix Models: Model Emulation, Model Discovery, and General Machine Learning

Parametric Matrix Models (PMMs) are a new class of implicit machine learning algorithms and techniques which aim to learn the underlying governing equations of data. This talk will give a conceptual and practical overview of PMMs for model emulation, highlight some ongoing work in using PMMs for model discovery, and show results demonstrating state-of-the-art parameter efficiency in general machine learning tasks. Finally, I will discuss ongoing theoretical efforts to extend PMMs to state-vector emulation and nonlinear problems as well as to unify PMMs with existing methods such as Dynamic Mode Decomposition, Proper Orthogonal Decomposition, and Eigenvector Continuation in a single framework.

Theorie-Seminar

Fernando Romero-Lopez (Uni Bern)
Hadronic resonances from Lattice QCD

The majority of known hadrons in the low-energy QCD spectrum are resonances observed in multi-particle scattering processes. First-principles determinations of the properties of these unstable hadrons are a crucial goal in lattice QCD calculations. Significant progress has been made in developing, implementing and applying theoretical tools that connect finite-volume lattice QCD quantities to scattering amplitudes, enabling determination of masses and widths of various hadronic resonances. In this talk, I will discuss recent advances in lattice QCD studies of meson-baryon resonances, including the Delta(1232) and Lambda(1405) resonances, as well as three-hadron resonances such as the doubly- charmed tetraquark.

Theorie-Seminar

Rajeev Singh (West University of Timisoara, Romania)
Stochastic relativistic advection-diffusion equation from the Metropolis

We study an approach to simulating the stochastic relativistic advection-diffusion equation based on the Metropolis algorithm. We show that the dissipative dynamics of the boosted fluctuating fluid can be simulated by making random transfers of charge between fluid cells, interspersed with ideal hydrodynamic time steps. The random charge transfers are accepted or rejected in a Metropolis step using the entropy as a statistical weight. This procedure reproduces the expected strains of dissipative relativistic hydrodynamics in a specific (and non-covariant) hydrodynamic frame known as the density frame. Numerical results, both with and without noise, are presented and compared to relativistic kinetics and analytical expectations. An all order resummation of the density frame gradient expansion reproduces the covariant dynamics in a specific model. In contrast to all other numerical approaches to relativistic dissipative fluids, the dissipative fluid formalism presented here is strictly first order in gradients and has no non-hydrodynamic modes. We will also present the extension to relativistic viscous hydrodynamics and its comparison with BDNK formalism.

Theorie-Seminar

Dean Lee (MSU)
Parametric Matrix Models

I give an introduction to a new machine learning approach called parametric matrix models, which are based on the matrix equations of quantum physics rather than the biology of neurons. Rather than fitting output functions according to some specified form, PMMs learn the underlying equations that produce the desired output, similar
to how physics problems are solved. I discuss the connection to eigenvector continuation and reduced basis methods, show the proof of the universal function approximation theorem, and then go through several applications to scientific computing as well as more general machine learning applications related to image recognition.

Theorie-Seminar

Shinya Wanajo (Albert Einstein Institute Potsdam)
Production of heaviest nuclei in neutron star mergers

The origin of r-process elements such as gold and uranium has long been a mystery in astrophysics. The discovery of an electromagnetic counterpart (kilonova) associated with the gravitational wave event GW170817 has confirmed that neutron star mergers are sites where the r-process occurs. However, whether neutron star mergers are the dominant sources of r-process nuclei in the universe remains uncertain. In this presentation, I will share our latest nucleosynthesis study results, which are based on magnetohydrodynamic simulations of neutron star mergers, as well as other potential sites such as black hole-neutron star mergers and collapsars.

Theorie-Seminar

Melissa Mendes (TU Darmstadt)
Investigating the nuclear equation of state from neutron star cooling and mass-radius information

Investigating the behavior of the nuclear equation of state (EOS) is an open research question. In particular, the study of neutron stars has been especially fruitful to probe the EOS at densities above saturation thanks to observations of its properties such as mass, radius, tidal deformability and temperature. In this talk, I discuss two works dealing with constraining the neutron star EOS. First, I use observations of the luminosity of fast cooling transiently-accreting neutron stars to investigate a possible first-order quark-hadron phase transition. Then, I discuss how new NICER mass-radius data combined with gravitational wave observations and chiral effective theory constraints provide information for the neutron star EOS.

Theorie-Seminar

Andrea Porro (TU Darmstadt)
Ab initio description of monopole resonances in light- and medium-mass nuclei

Giant monopole resonances have a long-standing theoretical importance in nuclear structure. The interest resides notably in the so-called breathing mode that has been established as a standard observable to constrain the nuclear incompressibility. The Random Phase Approximation (RPA) within the frame of phenomenological Energy Density Functionals (EDF) has become the standard tool to address giant resonances and extensive studies, have been performed throughout the years. A proper study of collective excitations within the ab initio framework is, however, missing. Additionally, the ab initio many-body methods developed over the past two decades encounter limitations when it comes to dealing with excited-state properties.

In this perspective, I will present a systematic ab initio predictions of (giant) monopole resonances. Ab initio Quasiparticle-RPA (QRPA) and Projected Generator Coordinate Method (PGCM) calculations of monopole resonances are compared in light- and mid-mass closed- and open- shell nuclei. Monopole resonances represent the starting point for exploring higher multipolarities, the goal in the medium term being to establish PGCM and QRPA as complementary tools in the development of a fundamental theory of nuclear excitations.

Theorie-Seminar

Silas Beane (University of Washington)
Unnuclear physics at large charge

After reviewing the unitary Fermi gas and relevant aspects of non-relativistic conformal symmetry (Schroedinger symmetry), I will introduce the superfluid effective field theory (EFT) that describes the Fermi gas at and near unitarity in the far infrared. This EFT admits a large-charge expansion which allows the systematic computation of large-charge n-point functions. I will discuss the potential relevance of the large-charge formalism to the study of special nuclear reactions with many low-energy neutrons in the final state.

Theorie-Seminar

Lotta Jokiniemi (TRIUMF)
Neutrinoless double-beta decay and how to probe it with muon capture

Neutrinoless double-beta decay is a hypothetical weak-interaction process in which two neutrons inside an atomic nucleus simultaneously transform into protons and only two electrons are emitted. Since the electrons are emitted without accompanying antiparticles, the process violates the lepton-number conservation and requires that neutrinos are Majorana particles, hence providing unique vistas in the physics beyond the Standard Model of particle physics. The potential to discover new physics drives ambitious experimental searches around the world. However, extracting interesting physics from the experiments relies on nuclear-theory predictions, which remain a major obstacle.

I will talk about two approaches to tackle this problem. First, I will discuss the evaluation of recent effective-field-theory corrections to the operators and their effect on the theory predictions based on phenomenological nuclear many-body methods. Then, I will discuss first-principles calculations of muon capture in light nuclei, which have the potential to shed light on the high-momentum-exchange currents driving neutrinoless double-beta decay.

Theorie-Seminar

Rob Pisarski (Brookhaven National Laboratory)
Why the chiral phase transition for three light flavors is so interesting

In QCD, the eta prime meson is heavy because the breaking of the anomalous U_A(1) symmetry is large. A simple argument suggests that it should then be easy to see a first order chiral transition for light quarks. Nevertheless, numerical simulations on the lattice see no evidence for such a first order chiral transition. I suggest that this occurs because the usual power counting for anomalous operators is more subtle than expected. This leads to numerous predictions for different numbers of quark flavors. The case of a single flavor is especially interesting. It also suggests novel experimental signals.

Theorie-Seminar

Isak Svensson (TU Darmstadt)
Bayesian uncertainty quantification in ab initio nuclear theory

The theory of the strong interaction - quantum chromodynamics (QCD) - is unsuited to practical calculations of nuclear observables and approximate models for nuclear interaction potentials are required. In contrast to phenomenological models, chiral effective field theories (chiral EFTs) of QCD grant a handle on the theoretical uncertainty arising from the truncation of the chiral expansion. Uncertainties in chiral EFT are preferably quantified using Bayesian inference, but quantifying reliable posterior predictive distributions for nuclear observables presents several challenges. First, chiral EFT is parametrized by unknown low-energy constants (LECs) whose values must be inferred from low-energy data of nuclear structure and reaction observables. There are 31 LECs at fourth order in Weinberg power counting, leading to a high-dimensional inference problem which I approach by developing an advanced sampling protocol using Hamiltonian Monte Carlo (HMC). This allows me to quantify LEC posteriors up to and including fourth chiral order. Second, the chiral EFT truncation error is correlated across independent variables such as scattering energies and angles; I model correlations using Gaussian processes. Third, the computational cost of computing few- and many-nucleon observables typically precludes their direct use in Bayesian parameter estimation as each observable must be computed in excess of 10^5 times during HMC sampling. However, eigenvector-continuation emulators today provide the necessary leverage to include observables beyond the two-nucleon sector in Bayesian inferences. In this talk I discuss the progress I made in this area during my PhD studies, presenting findings regarding the LEC inference problem as well as resulting posterior predictive distributions for nuclear observables.

Theorie-Seminar

Soeren Schlichting (Bielefeld University)
Collectivity in Heavy-Ion collisions - exploring the applicability of fluid dynamics far from equilibrium

High-energy heavy-ion collisions provide a unique environment to explore the properties of strong-interaction matter under extreme conditions. Since the theoretical description of the complex reaction dynamics from the underlying theory of QCD poses an outstanding challenge, a macroscopic description in relativistic hydrodynamics is commonly employed to describe the emergence of collective phenomena in heavy-ion collisions. In this talk, we will discuss recent progress to understand the non-equilibrium dynamics of QCD plasmas from kinetic theory, and assess the range of applicability of hydrodynamics as an effective description for non-equilibrium systems.

Theorie-Seminar

Mariam Gogilashvili (Florida State University)
Predicting Which Massive Stars Explode

At the end of their lives, most massive stars undergo core collapse. Some stars explode as a core-collapse supernova (CCSN) explosion leaving behind neutron stars (NS) while others fail to explode and collapse to stellar-mass black holes (BH). One of the major challenges in CCSN theory is to predict which stars explode and which fizzle. We develop an analytic force explosion condition (FEC) to predict which massive stars explode. The FEC depends upon four dimensionless parameters only: 1. net neutrino heating deposited in the gain region, 2. neutrino opacity that parameterizes the neutrino optical depth in the accreted matter near the neutron-star surface, 3. the integrated buoyant driving, and 4. the radial component of the Reynolds stress. The FEC promises to be an accurate explosion condition for multi-dimensional simulations as well as being useful diagnostic to measure a "distance" to explosion. I will present a progress in validating the FEC with multi-dimensional simulations and discuss potential to expand the model by including additional effects that may be important to predict explosions in nature

Theorie-Seminar

Marta Molero (Universita degli studi di Trieste)
Chemical evolution of neutron-capture elements across the Milky Way

Modelling the evolution of the elements in galaxies of different morphological types is a multidisciplinary and challenging task. Chemical evolution simulations must be able to follow ~ 13 billion years of evolution of a galaxy and also to keep track of the elements synthesized and ejected from every astrophysical site of interest. In this talk, I will give a general overview of the Chemical Evolution of Galaxies field describing both its aims and explaining which are the basic ingredients necessary to build a Chemical Evolution simulation. I will then focus on the main topic of my PhD: the study of the evolution of heavy elements abundances. The majority of elements beyond the Fe peak are produced by neutron capture processes which can be rapid (r-process) or slow (s-process) with respect to the beta-decay in nuclei. Understanding which are the astrophysical formation sites of these two processes has become one of the major challenges in chemical evolution. The s-process mainly takes place in low-intermediate mass stars during the asymptotic giant branch phase and in rotating massive stars, with the latter being particularly relevant at low metallicities. On the other hand, the r-process sites are still under debate, with possible main producers candidates being peculiar supernovae (magneto-rotational supernovae, MR-SNe) or merging of compact objects (neutron stars or neutron star-black hole). Although observations point towards merging neutron stars (MNS) as the major astrophysical r-process site, chemical evolution simulations still struggle to reproduce the abundance pattern of the [Eu/Fe] vs. [Fe/H] (with Eu being a typical r-process element) if MNS are the only producers of r-process material and realistic timescales for merging are assumed. In this talk, I will first present the main steps done in chemical evolution simulations to understand the origin of neutron capture elements and then I will show results from our latest work. We studied both the abundance patterns and the radial gradients of nine neutron-capture elements (Y, Zr, Ba, La, Ce, Eu, Mo, Nd, Pr) in the Galactic thin disc by means of a detailed two-infall chemical evolution model with state-of-the-art nucleosynthesis and timescales prescriptions. We compared our results with data from the sixth data release of the Gaia-ESO survey, which consists of 62 open clusters located at different Galactocentric distances and with ages ranging from 0.1 to 7 Gyr, and 1300 disc field stars, in order to underline which are the main uncertainties still present in the modelling of heavy elements.

Theorie-Seminar

Johannes Weber (Humboldt-Universitaet Berlin)
Hard Probes of Hot Nuclear Matter

The hot nuclear medium that permeated the early universe can be studied experimentally with heavy-ion collisions and through various theoretical approaches. New or upgraded experiments turn our attention to hard processes and a more fine-grained resolution of this primordial state of matter. In this endeavor quarkonia, open heavy flavors, and jets turn out to be versatile probes, which are usually described through models based on resummed perturbative QCD, AdS, and effective field theories. The lattice provides nonperturbative input and constraints to such models. In-medium bottomonia, the complex static quark-antiquark potential, as well as the heavy-quark momentum and the jet transverse momentum diffusion transport coefficients are key quantities where lattice gauge theory has recently achieved significant progress with major impact for heavy-ion phenomenology. I review these lattice results, relate them to phenomenological applications, and close with an outlook towards expectations for the next few years.

Theorie-Seminar

Theo F. Motta (TU Darmstadt and JLU Giessen)
A Stability Analysis of Inhomogeneous Phases in QCD

Understanding the phase structure of Quantum Chromodynamics (QCD) is of paramount importance for nuclear and particle physics. At large densities and low temperatures, many complex phases are expected to appear. This is where the lattice sign problem is unavoidable and extrapolation methods such as Taylor expansions are out-of-bounds. Alongside colour-superconductivity, quarkyonic matter, and so on, the possibility of a crystalline phase has been studied for over twenty years. In simplified models of QCD such as NJL or quark-meson models, these phases are present. However, no unambiguous determination exists that they appear in QCD. In this talk, I will discuss our efforts to develop a method of stability analysis that is compatible with full QCD via Dyson-Schwinger Equations.

Theorie-Seminar

Martin Obergaulinger (Valencia University)
Core-collapse supernovae with magnetic jets

Magnetic fields are a common feature of both the progenitors of core-collapse supernovae, i.e., massive stars, and of their remnants, neutron stars. If combined with rapid rotation, they can affect the explosion dynamics and eject a part of the gas in the form of jets along the rotational axis. Besides the high explosion energies, these events also differ from the majority of neutrino-driven supernovae by their nucleosynthetic yields and observables like the gravitational-wave signal. I will present recent simulations of a set of three-dimensional simulations combining magnetohydrodynamics and neutrino transport in which explosions with different degree of magnetic influence occur and highlight some of the key processes that determine the outcome.

Theorie-Seminar

Aman Abhishek (Institute of Mathematical Sciences, Chennai, India)
Towards a universal description of hadronic phase of QCD

Mean-field model quantum field theories of hadrons were traditionally developed to describe cold and dense nuclear matter and are by now very well constrained from the recent neutron star merger observations. We show that when augmented with additional known hadrons and resonances but not included earlier, these mean-field models can be extended beyond its regime of applicability. Calculating some specific ratios of baryon number susceptibilities for finite temperature and moderate values of baryon densities within mean-field approximation, we show that these match consistently with the lattice QCD data available at lower densities, unlike the results obtained from a non-interacting hadron resonance gas model. We also estimate the curvature of the line of constant energy density, fixed at its corresponding value
at the chiral crossover transition in QCD, in the temperature-density plane. The number density at low temperatures and high density is found to be about twice the nuclear saturation density along the line of constant energy density of 348 +- 41 MeV/fm^3. Moreover from this line we can indirectly constrain the critical end-point of QCD to be beyond 597 MeV mu_B for temperature 125 MeV.

Theorie-Seminar

Mark Alford (Washington University, St. Louis)
Is nuclear matter in neutron star mergers driven out of equilibrium?

In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on chemical (beta) equilibration and its consequences such as bulk viscosity and damping of oscillations.

Theorie-Seminar

Dam T. Son (University of Chicago)
Nonrelativistic conformal field theory and nuclear reactions

We develop a formalism of nonrelativistic conformal field theory, which is then used to describe neutrons at low energies. We show that the rates of nuclear reactions with emission of a few neutrons in the final state show a power-law behavior in the kinematic region where the emitted neutrons have almost the same momentum. We show how corrections to this power-law behavior can be computed using conformal perturbation theory.

Theorie-Seminar

Assistant Prof. Dr. Luka Leskovec
Baryonic Resonances in Lattice QCD

Theorie-Seminar

Sara Collins (Regensburg)
Properties of the baryon octet from lattice QCD

Numerous ongoing experimental investigations into physics beyond the Standard Model focus on nucleons as fundamental probes, prompting extensive efforts to extract nucleon structure observables on the lattice. This includes the determination of quantities like the weak charges and axial form factors. However, it is also interesting to extend such studies to hyperons, which have received less attention. Exploring the properties of hyperons provides valuable insights into the SU(3) flavor symmetry encoded in low-energy effective field theory descriptions. Moreover, studying their weak decays offers alternative means of determining the elements of the CKM matrix. As a first step we determine the spectrum, weak charges and sigma terms of the baryon octet controlling all sources of systematic uncertainty.

Theorie-Seminar

Frederic Noel (Uni Bern)
Mu->e conversion, LFV pseudoscalar decays, and nuclear charge densities

Mu->e conversion in nuclei gives one of the leading limits on BSM lepton-flavor violating (LFV) processes. In this process a muon bound to a nucleus converts into an electron without neutrinos. Upcoming measurements call for a more consistent theoretical description of mu->e conversion, which can be done model independently using an effective field theory frame work in terms of effective BSM operators. As it turns out, the relevant operators for the spin dependent part of mu->e conversion also mediates LFV pseudoscalar decays, which makes it possible to relate these processes and their experimental limits. Furthermore for the treatment of the bound state physics appearing in mu->e conversion, quantifiable knowledge on the charge densities of the considered nuclei is needed.
In this talk I will give an overview over our ongoing work on mu->e conversion, including some recent results regarding LFV pseudoscalar decays, as well as the determination of nuclear charge densities from electron scattering.

Theorie-Seminar

Saga Aurora Saeppi (TU Muenchen)
Exploring extremely dense matter with perturbative QCD

With LIGO and its friends observing colliding neutron stars, and astrophysicists measuring their radii and masses with unprecedented precision, understanding how dense QCD matter behaves is a particularly timely goal. I will approach this from the side of (very-)high-density theory: How do first-principles calculations in dense QCD in the small-coupling limit work, and how have they advanced in the last few years? Some of the advancements I will discuss in this talk include an efficient and simple way to incorporate the effects of quark masses in perturbative calculations, particularly useful for near-future calculations of the bulk viscosity, as well as an ongoing computation of the next-to-next-to-next-to-leading order pressure of cold dense QCD, where there are both concrete recent (and upcoming) results for the self-energy as well as improved theoretical methods necessary for finishing the full computation.

Theorie-Seminar

Zhonghao Sun (Oak Ridge National Laboratory)
Ab-initio computation of exotic nuclei

Precise and predictive calculations of the atomic nuclei from realistic nuclear force help us to understand how the fundamental interaction leads to the emergence of various exotic phenomena. The advances in computational power, emerging machine learning technology, and the development of many-body methods make it possible to perform uncertainty quantification and sensitivity analyses in the nuclear structure calculations. In this talk, I will report the progress of the ab-initio coupled-cluster method in describing spherical and deformed atomic nuclei. I will also introduce the quantified predictions of the neutron skin thickness of 208Pb and the drip line of oxygen isotopes.

Theorie-Seminar

Agnieszka Sorensen (INT Seattle)
The speed of sound of dense nuclear matter from heavy-ion collisions

The equation of state (EOS) of dense nuclear matter has been the center of numerous research efforts over the years. While numerous studies indicate that the EOS is relatively soft around the saturation density of nuclear matter, recent analyses of neutron star data strongly suggest that in the cores of neutron stars, where densities may reach several times that of normal nuclear matter, the EOS becomes very stiff - so stiff, in fact, that the speed of sound squared may substantially exceed the conformal limit of 1/3. This striking behavior inspires the research I will present in this talk.

I will discuss a novel way of using higher moments of the baryon number distribution, measured in experiments, to infer the speed of sound in dense nuclear matter created in low-energy heavy-ion collisions. I will then present the framework I developed to enable comprehensive hadronic transport studies of the influence of the dense nuclear matter EOS on experimental observables, and I will discuss implications for the speed of sound of dense nuclear matter based on a recent analysis using this framework.

Theorie-Seminar

Owe Philipsen (GU Frankfurt)
Chiral spin symmetry and the QCD phase diagram

Recently, an emerging chiral spin symmetry was discovered in the multiplets of lattice QCD hadron correlators for a temperature window above the chiral crossover. This symmetry is larger than the expected
chiral symmetry. It can only be approximately and dynamically realised when colour-electric quark-gluon interactions dominate the quantum effective action. This suggests the chiral spin symmetric regime to be of a hadron-like rather than partonic nature. After a brief review of the symmetry, I show independent evidence from meson screening masses and the pion spectral function, which support this picture. Finally, I discuss how this chiral spin symmetric band may continue across the QCD phase diagram, where it may smoothly connect to quarkyonic matter at low temperatures and high densities.

Theorie-Seminar

Frithjof Karsch (Bielefeld University)
QCD Phase Diagram and the Equation of State of Strong-Interaction Matter

Lattice QCD calculations at non-zero temperature and with non-vanishinq
chemical potentials provide a powerful framework for the analysis of the
phase structure of strongly interacting matter. Such calculations allow the determination of the crossover transition region at QCD with physical quark masses as well as the determination of the true chiral phase transition in the limit of vanishing light quark masses.

We present results on the determination of the pseudo-critical and chiral
phase transition temperatures as well as a new, high statistics determination of the QCD equation of state. We point out their importance for constraining the location of a possible critical end point in the QCD phase diagram. We furthermore present a new, high statistics determination of the QCD equation of state.

Theorie-Seminar

Renwick James Hudspith (GSI)
A complete lattice QCD determination of the hadronic light-by-light scattering contribution to the muon g-2

The g-2 of the muon provides a high-precision test of the Standard Model of particle physics, and a possible window into beyond the Standard Model physics. Currently, there is some tension between the theoretical prediction of this quantity and experiment. As experimental precision continues to improve it is paramount for theoretical computations to do so also, in hope of resolving this tension. One of the most poorly-known contributions to the theory calculation of the muon g-2 comes from hadronic light-by-light scattering. I will present an overview of our measurement of this contribution using lattice QCD techniques, where we have obtained the most precise determination to date.

Theorie-Seminar

Baha Balantekin (University of Wisconsin, Madison)
Collective Neutrino Oscillations and Quantum Entanglement

Entanglement of constituents of a many-body system is a recurrent feature of quantum behavior. Quantum information science provides tools, such as the entanglement entropy, to help assess the amount of entanglement in such systems. Many-neutrino systems are present in core-collapse supernovae, neutron star mergers, and the Early Universe. Recent work in applying the tools of quantum information science to the description of the entanglement in astrophysical many-neutrino systems is presented, in particular the connection between entropy and spectral splits in collective neutrino oscillations is elaborated.

Theorie-Seminar

Derek Teaney (Stony Brook)
Dynamics of the O(4) critical point in QCD

To motivate the simulations I review Lattice data on the chiral phase transition in QCD. Then I discuss the hydrodynamics of the chiral phase transition, reviewing the appropriate dynamical equations above, below, and during the phase transition. Then a present a simulation of the dynamics of the phase transition, which shows how goldstone modes appear dynamically. Finally I discuss soft pions in heavy ion collisions, which are enhanced relative to normal hydrodynamic simulations of heavy ion collisions. I suggest that this reflects the fingerprints of the O(4) critical point.

Theorie-Seminar

Lorenz von Smekal (Uni Giessen)
Real-time methods for spectral funcions

The real-time methods discussed and compared in this talk include classical-statistical lattice simulations, the Gaussian state approximation (GSA), and the functional renormalization group (FRG) formulated on the Keldysh closed-time path. The quartic anharmonic oscillator coupled to an external heat bath after Caldeira and Leggett thereby serves as an illustrative example where a benchmark solution can be obtained from exact diagonalization with constant Ohmic damping. To extend the GSA to open systems, we solve the corresponding Heisenberg-Langevin equations in the Gaussian approximation. For the real-time FRG, we introduce a novel general prescription to construct causal regulators based on introducing scale-dependent fictitious heat baths. As first field theory applications we have used our real-time FRG framework to calculate dynamical critical exponents for different dynamics.

Theorie-Seminar

Dr. Robert Pisarski (Brookhaven National Laboratory)
A potpourri in extreme QCD

I discuss some combination of topics in SU(N) gauge theories at nonzero temperature and density, including: the exact solution of the low energy excitations for cold, dense quarks in 1+1 dimensions (you'll learn what a Luttinger liquid is); how to represent timelike Wilson loops in Hamiltonian form (bit obvious after the fact); configurations with topological charge 1/N in SU(N) gauge theories without dynamical quarks.

Theorie-Seminar

Carolyn Raithel (Princeton Center for Theoretical Science)
Probing the Dense-Matter Equation of State with Neutron Star Mergers

Binary neutron star mergers provide a unique probe of the dense-matter equation of state (EOS) across a wide range of parameter space, from the cold EOS during the inspiral to the finite-temperature EOS following the merger. In this talk, I will discuss the influence of finite-temperature effects on the post-merger evolution of a neutron star coalescence. I will present a new set of neutron star merger simulations, which use a phenomenological framework for calculating the EOS at arbitrary temperatures and compositions. I will show how varying the properties of the particle effective mass affects the thermal profile of the post-merger remnant and how this, in turn, and influences the post-merger evolution. Finally, I will discuss several ways in which a future measurement of the post-merger gravitational waves can be used to constrain the dense-matter EOS.

Theorie-Seminar

Joanna Sobczyk (Uni Mainz)
Nuclear ab initio studies for neutrino oscillations

We are entering an era of high-precision neutrino oscillation experiments (T2HK, DUNE), which potentially hold answers to some of the most exciting questions in particle physics. Their scientific program requires a precise knowledge of neutrino-nucleus interactions coming from fundamental nuclear studies. Ab initio many-body theory has made great advances in the last years and is able to give relevant predictions for medium-mass nuclei important for the neutrino experiments.
In my talk I will give an overview of the recent progress that has been made in describing neutrino-nucleus scattering within the ab-initio coupled-cluster framework, combined with the Lorentz integral transform. These techniques open the door to obtaining nuclear responses (and consequently cross-sections) for medium-mass nuclei starting from first principles.

Theorie-Seminar

Aleksas Mazeliauskas (CERN)
Many-body QCD phenomena in high-energy proton and nuclear collisions

The emergence of macroscopic medium properties over distances much smaller than a single atom is a fascinating and non-trivial manifestation of the many-body physics of Quantum Chromodynamics in high-energy nuclear collisions. The observation of collective particle behaviour in collisions of heavy-ions at the Relativistic Heavy Ion Collider at BNL and the Large Hadron Collider at CERN is strong evidence that a new exotic phase of matter called the Quark-Gluon Plasma is created in these large collision systems. However, the striking discovery of the very same collective phenomena in much smaller systems of proton-proton and proton-lead collisions at the LHC has confounded heavy-ion physics expectations and is not predicted by the conventional high-energy physics picture of elementary collisions. One of my main research goals is to uncover the physical origins of this universal macroscopic behaviour. In this talk I will review the recent progress and future plans in developing theoretical description and experimental tests of these effects within the non-Abelian quantum field theory of strong interactions.

Theorie-Seminar

Prof. Dr. Thomas Schaefer (North Carolina State University)
Stochastic fluid dynamics: Effective actions and new numerical tools

Recent interest in stochastic fluid dynamics is motivated by the search for a critical point in the QCD phase diagram. I will discuss old ideas about effective actions that have recently received new interest, and some new ideas about how to implement stochastic fluid dynamics in numerical simulations.

Theorie-Seminar

Lotta Jokiniemi (University of Barcelona)
What Can We Learn from Double-Beta Decay and Ordinary Muon Capture?

Observing neutrinoless double-beta (0vbb) would undoubtedly be one of the most anticipated breakthroughs in modern-day neutrino and nuclear physics. This is highlighted by the number of massive experiments worldwide trying to detect the phenomenom, as well as the efforts of numerous theory groups trying to probe the process from different theory frameworks. When observed, the lepton-number-violating process would provide unique vistas beyond the Standard model of particle physics. However, the half-life of the process depends on coupling constants whose effective values are under debate, and nuclear matrix elements (NMEs) that have to be extracted from theory. Unfortunately, at present different many-body calculations probe matrix elements whose values disagree by more than a factor of two. Hence, it is crucial to gain a better understanding on both the coupling constants and the NMEs in order to plan future experiments and to extract the beyond-standard-model physics from the experiments.

In my seminar I will discuss how the theory predictions can be improved either directly by investigating corrections to the 0vbb decay matrix elements, or indirectly by studying alternative processes that can be or have been measured. First, I will introduce our recent work on a new leading-order correction to the standard 0vbb-decay matrix elements in heavy nuclei. Then, I will discuss the potential of ordinary muon capture as a probe of 0vbb decay, and discuss the results of our recent muon-capture studies.

Theorie-Seminar

Laura Sagunski (Goethe Universtaet Frankfurt)
Gravitational Waves from the Dark Side of the Universe

The first ever direct detections of gravitational waves from merging black holes and neutron stars by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector have opened a fundamentally new window into the Universe. Gravitational waves from binary mergers are high precision tests of orbital dynamics and provide an unprecedented tool to probe fundamental physics. Not only do they allow to test gravity under extreme conditions, but also to address the very fundamental open questions in the evolution of our Universe, namely the mysteries of dark matter and dark energy (or possible modifications of general relativity). In my talk, I will show how we can turn binary mergers into cosmic labs where we can test the very foundations of general relativity and explore the existence of new interactions and particles, like axions, which could be the dark matter.

Theorie-Seminar

Felipe Attanasio (Uni Heidelberg)
QCD equation of state via the complex Langevin method

The equation of state of hadronic matter is of high importance for
many fields, ranging from heavy-ion collisions to neutron stars. Non-
perturbative methods to simulate QCD encounter difficulties at finite
chemical potential mu due to the so-called sign problem. We employ the complex Langevin method to circumvent this problem and carry out
simulations at a variety of values for temperature and mu. We present
results on the pressure, energy and entropy equations of state, as well
as a numerical observation of the Silver Blaze phenomenon.

Theorie-Seminar

Vittorio Soma (CEA Saclay)
A novel many-body method for the ab initio description of doubly open-shell nuclei

Recent developments in many-body theory and in the modelling of nuclear Hamiltonians have enabled the ab initio description of a considerable fraction of atomic nuclei up to mass A~100. In this context, one of the main challenges consists in devising a method that can tackle doubly open-shell systems and at the same time scales gently with mass number. This would allow both to access all systems below A~100 and to open up perspectives for extending ab initio calculations to the whole nuclear chart.

In this seminar I will present a recently proposed many-body approach that aims towards this objective. After introducing the formalism based on a multi-reference perturbation theory [1], I will discuss the first numerical applications [2,3] together with considerations on the state of the art and future perspective in ab initio nuclear structure.

[1] M. Frosini et al., arXiv:2110.15737
[2] M. Frosini et al., arXiv:2111.00797
[3] M. Frosini et al., arXiv:2111.01461

Theorie-Seminar

Nicolas Wink (TU Darmstadt)
Elementary correlation functions and their applications in QCD

In this talk we explore the calculation of elementary correlation functions in the context of QCD. We consider these correlation functions in Euclidean and Minkowski space-time. For the latter we consider direct calculations based on dimensional regularization in Dyson-Schwinger equations in a scalar theory and Yang-Mills. Additionally, we present results from analytic continuation of Euclidean lattice data based on Gaussian Process Regression in full QCD. Afterwards we turn our attention to the calculation of transport coefficients in Yang-Mills, based on gluon spectral functions obtained previously. In the last part of the talk we consider field dependencies in functional Renormalization Group equations. We focus in particular on technical challenges at high densities and how to overcome them.

Theorie-Seminar

Andreas Ipp (Vienna University of Technology)
Simulating the Glasma stage in heavy ion collisions

The earliest stage right after the collision of ultrarelativistic heavy ions is known as the Glasma stage. It is characterized by strong anisotropic color fields and forms the precursor of the quark-gluon plasma. In this talk, I present our approach to simulating the Glasma using a colored particle-in-cell simulation. With this method, we can access the full 3+1 dimensional space-time picture of the collision process. These simulations are inherently plagued by numerical Cherenkov instability, and we show how an improved action can cure this instability using a semi-implicit scheme. Simulation results can be checked in a dilute limit against analytic calculations. I will present results for observables such as the rapidity profile or momentum broadening of jets within the Glasma stage.

Theorie-Seminar

Weiguang Jiang (Chalmers)
Exploring non-implausible nuclear-matter predictions with delta-full chiral interactions

Advances in quantum many-body methods and computing allow us to study the finite nuclei and infinite nuclear matter with realistic interaction models based on chiral effective field theory. We develop the nuclear matter emulators and introduce the robust statistical approach called history matching to explore the non-implausible nuclear-matter predictions with chiral interactions. We studied 1.6*10^6 non-implausible interaction samples in a huge LECs domain and reveal the connection between the finite nuclei and nuclear matter saturation properties.

Theorie-Seminar

Bastian Kubis (Uni Bonn)
Hadronic contributions to the muon's anomalous magnetic moment from analyticity

The first new experimental results on the anomalous magnetic moment of the muon from Fermilab, published in April 2021, confirm the tension with the Standard Model prediction, now at 4.2 sigma. The uncertainty
in the theory prediction is by far dominated by hadronic effects. I discuss how different important contributions can be made more precise by using rigorous theoretical constraints, especially due to analyticity: this includes hadronic vacuum polarization due to 3 pi and pi^0 gamma intermediate states, and hadronic light-by-light scattering via the largest individual contribution therein, the pi^0-pole term. The latter is determined in terms of the pi^0 transition form factor, for which a representation that incorporates all low-lying singularities and matches correctly onto the asymptotic behaviour expected from perturbative QCD has been derived. Further, ongoing, extensions of this work will briefly be mentioned.

Theorie-Seminar

Cristina Manuel Hidalgo (Instituto de Ciencias del Espacio, Barcelona)
Chiral plasmas and collisional energy loss

Systems made up by massless fermions but with unequal right-handed and left-handed populations have lately attracted great interest
for its wide applications in different physical scenarios. New transport phenomena associated to the quantum chiral anomaly appear in these systems, modifying the conventional hydrodynamical equations. I will discuss the relevant ingredients to study different aspects of chiral plasmas physics, such as the appearance of chiral plasma instabilities, or the fact that the chiral imbalance also affects the quasiparticles in the plasma. In particular, I will discuss the fermion damping rate and the collisional energy loss.

Theorie-Seminar

Mikhail Stephanov (University of Illinois Chicago)
Deterministic randomness in relativistic hydrodynamics

We usually think of hydrodynamics as a deterministic description of
fluid motion. The focus of this talk is on random fluctuations in
hydrodynamics caused by thermal noise, inherent in a system with
dissipation. The interest in this subject is driven by the progress of
heavy-ion collision experiments and, in particular, by the search for
the QCD critical point at the Relativistic Heavy-Ion Collider. I will
discuss the role the fluctuations play in hydrodynamics and how we can
describe their evolution in a deterministic formalism.

Theorie-Seminar

Gert Aarts (Swansea University)
A physicist's approach to machine learning

In recent years applications of machine learning in the physical sciences have increased substantially. In this talk I will discuss some recent developments, starting from "standard" classification problems of phase transitions in statistical physics. This will be followed by giving a physical interpretation of machine learning functions as observables in a statistical system, paving the way to include them in Hamiltonians. Finally, I will speculate on whether our experience in quantum field theory can be exploited to further develop machine learning frameworks.

Theorie-Seminar

Jose Pons (Universitat d'Alacant)
Magneto-thermal evolution of neutron stars as a probe of dense matter properties

I will review the general theory of long-term thermal evolution of neutron stars (a.k.a. "neutron star cooling") with a special focus on the effects of strong magnetic fields. After discussing the interplay between magnetic and thermal evolution and the observational facts that are usually employed to constrain the theories, I will discuss in some more detail a particular example: the possible observational evidence of the "nuclear pasta" phase, in the inner crust of neutron stars. The main facts leading to our conclusions will be highlighted, with pros and cons.

Theorie-Seminar

Andreas Ekstroem (Chalmers University of Technology)
Precision nuclear theory

Some ab initio nuclear interaction models work better than others and it is not clear why. We are using methods from computational statistics to generate new knowledge about the strong nuclear interaction and our models thereof. In this seminar I will outline some of these methods and present some recent results. I will also present an emulation method that allows for the computation of bulk properties of an atomic nucleus for a million of different model parameters in less than one hour on a standard laptop. The equivalent set of ab-initio coupled-cluster computations would require about 20 years. This speedup enables a range of statistical analyses of nuclear interaction models, and new ways to predict observables across the nuclear chart.

Theorie-Seminar

Gergeley Endroedi (Uni Bielefeld)
Magnetized QCD on the lattice

Strong magnetic fields are known to have a significant impact on
strongly interacting matter, playing a relevant role for a range
of physical systems like magnetized neutron stars, off-central
heavy-ion collisions or the evolution of the early universe. How
does the magnetic field influence strongly interacting quarks
and gluons? This question may be answered by first-principles
lattice QCD simulations. In this talk I will give an overview about recent developments in this field with a special focus on the determination of the phase diagram and the equation of state on the lattice.

Theorie-Seminar

Tyler Gorda (TU Darmstadt)
Dense QCD matter and neutron stars

The cores of massive neutron stars (NSs) may probe an extremely interesting regime of the phase diagram of quantum chromodynamics (QCD): one where the degrees of freedom may change from colorless hadrons to colored quarks and gluons. However, such a region is inaccessible to current nuclear-theory or high-density perturbative QCD (pQCD) techniques. As such, NSs provide an important window into a theoretically inaccessible region of the QCD equation of state (EOS). In this talk, I will discuss two specific topics. First, I will detail our current phenomenological program to constrain the physical properties of the QCD EOS at all densities by extrapolating the known, controlled nuclear and pQCD EOSs to intermediate densities where they can connect with astrophysical NS observables. This allows us to address questions as to the phase of matter inside these objects. Secondly, I will discuss our ongoing effort to improve the convergence of the pQCD EOS, by calculating higher-order corrections to the pressure of cold quark matter. Such an improved EOS would, through our extrapolation program, allow for more stringent constraints on the QCD EOS at all densities.

Theorie-Seminar

Maria Paola Lombardo (INFN-Laboratori Nazionali di Frascati)
Universal (?) scaling of QCD from Wilson fermions simulations

We study the scaling properties of QCD in temperature and mass close to the thermal crossover, and for quark masses ranging from the heavy quark regime to the physical values. The lattice results are obtained in the fixed scale approach, either with anisotropic simulations with Nf=2+1 flavours, and with simulations of Nf=2 +1+1 flavours at maximal twist. We propose a simple combination of chiral observables, which reduces the additive renormalizations and the contribution from the regular terms in the equation of state, thus helping the assessment of the hypothesized universal behaviour.

Theorie-Seminar

Alexander Rothkopf (University of Stavanger)
Open Quantum Systems - Precision Thermometry at the Extremes

The study of quantum systems coupled to an environment plays a vital role in how we measure temperatures of the coldest and hottest matter in the universe. The strategy relies on introducing impurities into the system of interest and on observing how these probe particles evolve towards or in equilibrium with their surroundings, from which we may in turn deduce the thermal properties of that environment. Originally studied in the context of condensed matter physics, open quantum systems nowadays provide a common language to research spanning multiple orders of magnitude in temperature, ranging from Bose Einstein condensates made of ultracold atoms to the Quark-Gluon plasma created in ultra-relativistic collisions of heavy ions. We will explore how polaron impurities in the former and quarkonium particles in the latter are two manifestations of quantum Brownian motion, a phenomenon ideally described by open quantum systems.

Theorie-Seminar

Parikshit Junnarkar (TU Darmstadt)
Studies of multi-quark states from Lattice QCD

Lattice QCD has made impressive progress in recent years in spectroscopy of multi-quark states. In this talk, I will present an overview of the lattice QCD methodology in studying multi-quark states. These will be six quark states (two-baryons) and four quark states (tetraquarks). In particular, I will present and discuss results of two-baryon states in the SU(3) singlet channel known as the H-dibaryon and also discuss predictions of exotic two baryon states with heavy quarks. In addition, I will also present an overview of the doubly heavy tetra quark states and its cousins.

Theorie-Seminar

Tyler Gorda (TU Darmstadt)
Dense QCD matter and neutron stars

The cores of massive neutron stars (NSs) may probe an extremely interesting regime of the phase diagram of quantum chromodynamics (QCD): one where the degrees of freedom may change from colorless hadrons to colored quarks and gluons. However, such a region is inaccessible to current nuclear-theory or high-density perturbative QCD (pQCD) techniques. As such, NSs provide an important window into a theoretically inaccessible region of the QCD equation of state (EOS). In this talk, I will discuss two specific topics. First, I will detail our current phenomenological program to constrain the physical properties of the QCD EOS at all densities by extrapolating the known, controlled nuclear and pQCD EOSs to intermediate densities where they can connect with astrophysical NS observables. This allows us to address questions as to the phase of matter inside these objects. Secondly, I will discuss our ongoing effort to improve the convergence of the pQCD EOS, by calculating higher-order corrections to the pressure of cold quark matter. Such an improved EOS would, through our extrapolation program, allow for more stringent constraints on the QCD EOS at all densities.

Theorie-Seminar

Tanja Hinderer (University of Amsterdam)
Probing subatomic physics with gravitational waves from neutron star binary inspirals

The gravitational waves from merging binaries carry unique information about the internal structure of compact objects. This is of major interest for neutron stars, offering the possibility for advancing our understanding matter and fundamental interactions in largely unexplored regimes. I will discuss the imprints of neutron star matter on the gravitational waves during the relatively clean, cumulative inspiral epoch, and the need for modeling these effects with a tapestry of approximation schemes for the interplay of dynamical gravity and matter. I will summarize what we have learned from recent measurements and conclude with an outlook onto the remaining challenges and exciting prospects for the next years as gravitational-wave science continues to move towards an era of precision physics.

Theorie-Seminar

Sungtae Cho (Kangwon National University)
Charmed hadron production in heavy ion collisions

We discuss the production of charmed hadrons in heavy ion collisions based on both the statistical and coalescence models. Starting from the investigation on estimated yields of charmed hadrons in the statistical hadronization model, we consider in the coalescence model transverse momentum distributions of those hadrons produced at quark-hadron phase transition in heavy ion collisions. We also consider the transverse momentum distribution of exotic hadrons such as Tcc and X(3872) mesons, and study transverse momentum distribution ratios between various charmed hadrons. We show that the transverse momentum distribution ratios between charmed hadrons are closely related to not only kinds and numbers of quarks but also the interplay between constituent quarks of those hadrons. We also discuss elliptic flows of charmonium states, and argue the possible relation between elliptic flows and wave function distributions in momentum space.

Theorie-Seminar

Erik Olsen (Universite Libre de Bruxelles)
Uncertainty in the Nuclear Energy Density Functional: Bayesian Fits, Odd Nuclei, and Going Beyond the Mean Field

Understanding astrophysical observables and phenomena requires a thorough knowledge of various properties of nuclei all over the nuclear chart. Since most of these systems are inaccessible through experiment, theoretical predictions are necessary. At present, nuclear Density Functional Theory is the only method available which can reach these systems while maintaining a microscopic character. Its key ingredient, the nuclear energy density functional, is an effective interaction based on one-body local densities and currents which contains a number of coupling constants whose values are optimized to experimental data and/or pseudo-data. Developing this interaction to minimize its root-mean-square error with respect to certain observables is crucial for more accurate astrophysical predictions. Past procedures in this endeavor will be discussed, as well as current plans to perform fits using Bayesian methodologies. Efforts to incorporate beyond-mean-field effects through the generator coordinate method and odd-mass nuclei into the fitting procedure will also be examined.

Theorie-Seminar

Yeunhwan Lim (TU Darmstadt)
Nuclear Equation of State for Hot Dense Matter

Nuclear equation of state (EOS) is constructed with energy density functional (EDF) and liquid drop model (LDM) technique. Compared with the classical LDM approach containing alpha particle, deutron, triton, and helio are added to construct nuclear EOS. Energy density functional parameters are constrained by theoretical neutron matter calculation, symmetric nuclear matter properties, and maximum mass of neutron stars. The nuclear surface tension and the critical temperature necessary for the free energy of finite nuclei are calculated in a consistent way. In this talk, I will present and discuss the current results obtained from LDM and EDF with most recent parameters.

Theorie-Seminar

Artem Volosniev (Institute of Science and Technology Austria)
Universal bound states of a few charged particles

Shallow bound states whose spatial extent is significantly larger than the range of the binding potential are often universal, i.e., their properties are independent of the shape of the underlying interactions. These states are often studied because they have no classical counterpart.
Moreover, they are used as models of important physical systems, e.g., halo nuclei and Efimov states in cold-atom set-ups. In Ref. [1], we study universality of shallow bound states of a few (two, three, four) charged particles. The interaction between particles has a short-range attractive part, and a long-range repulsive part, which is given by the Coulomb potential. First, we assume that the attractive part has a vanishing range. The corresponding two-body interaction leads to a family of universal states whose properties are determined by a set of scaling laws (the scales are given by the Coulomb modified scattering length, the Sommerfeld parameter, and a three-body parameter). Second, we study weakly-bound states in finite-range potentials. We show that these states cannot be studied using the universal scaling laws from above -- the effective range corrections are important and cannot be neglected.

[1] C. Schmickler, H.-W. Hammer and A. Volosniev, arXiv:1904.00913 (to appear in Physics Letters B).

Theorie-Seminar

Noriyuki Sogabe (Keio University)
New dynamic critical phenomena in nuclear and quark superfluids

We study the static and dynamic critical phenomena near the possible high-density QCD critical point in the superfluid phases of nuclear/quark matter. In particular, we find that its dynamic universality class is different not only from that of the high-temperature QCD critical point between the hadron and quark-gluon-plasma phases, but also from those universality classes studied in condensed matter systems so far. We argue that this novelty stems from the interplay between the chiral criticality and the presence of the superfluid phonon---a feature specific for the high-density QCD critical point.

Theorie-Seminar

Joaquin E. Drut (University of North Carolina)
Scale anomalies, crossovers, and the virial expansion of spin-1/2 fermions

Theorie-Seminar

Dominik Schwarz (Uni Bielefeld)
Gravitational waves from inspiralling compact binaries in conformal gravity

Mannheim's model of conformal gravity is claimed to describe universal properties of galaxy rotation curves without dark matter. In this talk I will discuss the emission of gravitational waves from inspiralling compact binaries in the context of conformal gravity models. These models exhibit both a massless and a massive spin 2 graviton, which makes the analysis of the observed gravitational wave events in these models very different from the generic study in general relativity. An analysis at leading order is performed to show that Mannheim's model can be ruled out from the observation of a merger of two neutron stars. Other parameter regimes of conformal gravity turn out to be indistinguishable from general relativity for the observed gravitational wave events and offer interesting candidate theories for a theory of quantum gravity.

Theorie-Seminar

Thomas Schaefer (North Carolina State University)
Critical behavior of the bulk viscosity in QCD

We discuss the role of thermal fluctuations in
fluid dynamics, with a particular emphasis of
the enhancement of the bulk viscosity near a
possible critical endpoint in the phase diagram
of QCD.

Theorie-Seminar

David Blaschke (University of Wroclaw)
Boiling QCD in supernova explosions and merger events

n a recent article [1] we have demonstrated that a first order
deconfinement phase transition (like boiling water) acts as an explosion
mechanism for very massive stars (50 M_sun), thus solving the
long-standing puzzle of the unknown explosion mechanism.
With the same EoS we were able to show that the postmerger gravitational
wave (GW) signal shows a significant deviation from the systematics
of peak frequency vs. radius of the source that was obtained for purely
hadronic equations of state [2]. Thus we could suggest an observable
signal for a strong phase transition in a compact star merger that
could be verified or falsified as soon as postmerger GW will be detected.
I will explain the theory background for the corresponding hybrid
quark-hadron matter EoS [3] that gives these interesting features and
discuss the possible implications for the structure of the QCD phase
diagram.

[1] T. Fischer et al., Nature Astronomy 2, 980 (2018)
[2] A. Bauswein et al., Phys. Rev. Lett. 120, 061102 (2019)
[3] M. Kaltenborn et al., Phys. Rev. D 96, 056024 (2017)

Theorie-Seminar

Johann Haidenbauer (Juelich)
Hyperon-nucleon interaction in few-body systems and in heavy ion collisions

Over the last few years the Julich-Bonn-Munich Group has performed
extensive studies of the baryon-baryon interaction involving strange
baryons (Lambda, Sigma, Xi) within chiral effective field theory. An
overview of the achieved results will be presented, with emphasis on
baryon-baryon scattering in the strangeness S=-1 sector. Predictions
for few- and many-body systems involving hyperons will be reported.
Furthermore, the possibility to constrain those interactions by
information on two-particle momentum correlation functions as measured in heavy ion collisions or in high-energetic proton-proton collisions will be addressed.

Theorie-Seminar

Dietrich Roscher (Universitaet Koeln)
Fractionalization in spin systems: an FRG perspective

In the last decades, a plethora of new phenomena and structures has been found in low-energy condensed matter systems that seem to defy the Landau paradigm of phase transitions. Oftentimes, effective theories with certain topological features and fractionalized degrees of freedom are best suited to describe the experimental findings. Unfortunately, writing down such an effective theory and understanding its relation to the accepted microscopic model for the actual material is usually not the same thing.
In this talk, I show how functional renormalization group can be employed to systematically construct the effective action of spin systems in a so-called spin liquid phase. Unexpectedly, the common toolbox of spontaneous symmetry breaking is well suited for this task and can be adapted to develop an understanding of phenomena that are often considered to be inherently "topological". Besides making predictions for hitherto poorly understood physical systems, functional RG thus provides a neat perspective on fractionalization and emergent gauge fields in strongly correlated spin systems.

Theorie-Seminar

Johannes Weber (MSU)
Quarkonium Free Energy on the lattice and in effective field theories

Quarkonia within the quark-gluon-plasma have been suggested as an effective thermometer of the hot QCD medium, as their properties are modified due to color screening and thermal dissociation. I discuss correlation functions of spatially separated static quark-antiquark
pairs in (2+1)-flavor QCD in order to elucidate the onset and nature of color screening at high temperatures. I perform lattice calculations in a wide temperature range, 140 < T < 5814 MeV, using the highly improved staggered quark action and several lattice spacings to control discretization effects and compare to results from EFT-resummed weak-coupling approaches.

Theorie-Seminar

Laura Moschini (Johannes Gutenberg-Universitaet Mainz)
Solving the apparent inconsistency between GSI and RIKEN estimates of 11Be dB(E1)/dE

The breakup of 11Be, the archetypal one-neutron halo nucleus, is a particularly interesting case because, due to its short lifetime, it is one of the only ways to infer information about its structure. In that reaction, the halo neutron dissociates from the core during the collision with a target. When performed on a heavy target, like lead, the reaction is dominated by the E1 transition from the ground state. This transition is characterized by the dB(E1)/dE. This strength has been inferred from two experiments, one performed at 520AMeV at GSI [1] and the other at about 70AMeV at RIKEN [2]. Strangely the analyses of both experiments provide different E1 strengths. In this work we reanalyze them using the eikonal approximation to elucidate this discrepancy. To analyze the RIKEN data we adopt the dynamical eikonal approximation (DEA), which works well at intermediate energies; while for the GSI experiment we have developed a model for the high-energy collision properly taking into account relativistic effects, on both kinematics and dynamical aspects [3,4]. Our eikonal model includes a consistent treatment of both nuclear and Coulomb interactions at all orders. The description of the 11Be structure is provided by Halo-EFT [5,6] fitting the low- energy constants of this description onto structure observables, like the ANC of the bound states and phaseshifts in the continuum, predicted by an ab initio calculation [7]. Our cross sections for the 11Be breakup are in excellent agreement with both RIKEN and GSI data [6,8]. The dB(E1)/dE extracted from our structure model is in agreement with the RIKEN result, as well as the ab initio prediction [7]. We can conclude that the discrepancy between GSI and RIKEN E1 strengths arises from the method applied to extract this quantity from the experimental data. This new way of analyzing nuclear reactions performed to study the structure of nuclei away from stability has been extended to the case of 15C, another one-neutron halo nucleus, whose breakup has been measured at GSI and RIKEN at 605 and 68AMeV respectively [9,10]. In both cases, our reaction models have led to excellent agreement with the data [11].
[1] R. Palit et al., Phys. Rev. C 68, 054606 (2003)
[2] N. Fukuda et al., Phys. Rev. C 70, 054606 (2004)
[3] G. Satchler, Nucl. Phys. A 540, 533 (1992)
[4] A. Winther and K. Alder, Nucl. Phys. A 319, 518 (1979)
[5] H.-W. Hammer, C. Ji, D. R. Phillips, J. Phys. G 44, 103002 (2017) [6] P. Capel, D. Phillips and H. Hammer, Phys. Rev. C 98, 034610 (2018) [7] A. Calci et al., Phys. Rev. Lett. 117, 242501 (2016)
[8] L. Moschini and P. Capel, Phys. Lett. B 790, 367-371 (2019)
[9] U. Datta Pramanik et al., Phys. Lett. B 551, 63-70 (2003)
[10] T. Nakamura et al., Phys. Rev. C 79, 035805 (2009)
[11] L. Moschini, J. Yang and P. Capel, in preparation

Theorie-Seminar

Matteo Bugli (Department of Astrophysics (DAp), CEA Saclay)
The impact of non-dipolar magnetic fields on core-collapse supernovae

The characteristics of the initial magnetic field present in a supernova progenitor prior to collapse and the dynamics of the field amplification due to different dynamo mechanisms (such as MRI, convective motions, etc.) are to this date quite uncertain.
We investigate the effects of multipolar magnetic field topologies of different radial extents on the dynamics of core-collapse supernovae and the properties of the forming proto-neutron star (PNS). Using axisymmetric relativistic MHD simulations, we find that higher multipolar magnetic configurations lead to generally less energetic explosions, with the central PNS increasing its spin and becoming more massive.
Models with a low order multipolar configuration tend to produce more oblate PNS which in some cases are surrounded by a rotationally supported toroidal structure. This change is the PNS shape can be directly associated with higher neutrino luminosities along the equatorial plane but smaller along the poles.

Theorie-Seminar

Kari Rummukainen (University of Helsinki)
Probing particle physics with gravitational waves

Violent processes in the early universe can produce gravitational waves, which may be observable in future gravitational wave detectors, for example, the European Space Agency LISA satellite constellation. The primordial gravitational waves are a signal of physics beyond the Standard Model. In this talk, I describe how first-order phase transitions can generate gravitational waves and what kind of imprint they leave on the gravitational wave spectrum.

Theorie-Seminar

Francesca Cuteri (Goethe-Universtaet Frankfurt)
Lattice explorations of the QCD phase diagram

Knowledge of the nature of the chiral phase transition of QCD with two flavors of massless quarks is of great importance for further progress in various directions of particle and heavy ion physics. The closeness of the light quark mass values realized in nature to the chiral limit, makes it very plausible that the thermal transition of physical QCD, both at zero and at nonzero baryon density, might be affected by remnants of the chiral universality class.

However, the direct extraction, using lattice simulations, of the order of the chiral transition of QCD at zero chemical potential, with two dynamical flavors of massless quarks, has proven to be a formidably difficult task. A first order region is found in the chiral limit only on coarse lattices and employing unimproved fermion discretizations, but whether it survives in the continuum limit is yet far from being known.

This situation motivates attempts to better constrain the first-order region by studying its extension in additional parameter directions, which might allow for controlled (by universality arguments) extrapolations to the chiral limit. These attempts will possibly be providing more insight and the wanted result at comparatively smaller costs. Also the dependence of the chiral transition on the number of light degenerate flavors, re-interpreted as continuous parameter in the path integral formulation, is considered as a means to perform controlled chiral extrapolations to the chiral limit.

Theorie-Seminar

Caroline Robin (University of Washington)
Charge-exchange modes and weak-interaction processes in Relativistic Nuclear Field Theory

Nuclear excitations with isospin transfer play a crucial role in our understanding of nuclear structure, particle physics and astrophysics. A precise description of such transition modes is needed to compute the rates of weak interaction processes such as single- or double-beta decay which can provide information on the nature of neutrinos and are needed for the modeling of the r-process nucleosynthesis.
In this talk I will present a theoretical approach to the description of charge-exchange modes in nuclei. This method describes the nucleus as a system of relativistic nucleons interacting via effective meson exchange and applies nuclear field theory to account for inter-nucleon correlations emerging from the coupling between nucleons and collective vibrations. In the charge-exchange channel the particle-vibration coupling generates a time-dependent proton-neutron interaction, in addition to the static pion and rho-meson exchange, which induces fragmentation and spreading of the transition strength. Such dynamical effects are essential for an accurate description of giant resonances and low-energy modes, and have a great impact on the calculation of weak-interaction rates and on the quenching of the Gamow-Teller strength. I will present some applications to Gamow-Teller transitions and weak decays in mid-mass and heavy nuclei.

Theorie-Seminar

Arianna Carbone (ECT*)
Predicting nuclear matter at finite-temperature with the use of chiral interactions

Advancing the study of infinite nuclear matter has important implications on many branches of nuclear science: from the bulk properties of exotic nuclei to the equation of state of neutron star matter. After we have extended the self-consistent Green's function (SCGF) theory to account for three-nucleon forces, it is now possible to make reliable predictions of nucleonic matter at both zero and finite temperatures and with full chiral interactions, a task that was not possible until some years ago. The talk will present the SCGF approach as a very convenient way to investigate microscopic and thermodynamical properties of nucleonic matter. We will see how the prediction of the liquid-gas phase transition critical temperature in symmetric matter appears to be in reasonable agreement with experimental outcomes. Furthermore, I will present first-principle tests of thermal approximations used in equations of state to study stellar processes, which questions the validity of such astrophysical simulations.

Theorie-Seminar

Juergen Berges (Universitaet Heidelberg)
Nonthermal fixed points and far-from-equilibrium hydrodynamics: from the quark-gluon plasma to cold atoms

Theorie-Seminar

Nicole Vassh (University of Notre Dame)
Fission and lanthanide production in r-process nucleosynthesis

The observations of the GW170817 electromagnetic counterpart last year suggested lanthanides were produced in this neutron star merger event. Lanthanide production in heavy element nucleosynthesis is subject to large uncertainties from nuclear physics and astrophysics unknowns. Specifically, the rare-earth abundance peak, a feature of enhanced lanthanide production at A~164 seen in the solar r-process residuals, is not robustly produced in r-process calculations. The proposed dynamical mechanism of peak formation requires the presence of a nuclear physics feature in the rare-earth region which may be within reach of experiments performed at, for example, the CPT at CARIBU and the upcoming FRIB. To take full advantage of such measurements, we employ Markov Chain Monte Carlo to "reverse engineer" the nuclear masses capable of producing a peak compatible with the observed solar r-process abundances and compare directly with experimental mass data. Here I will present our latest results given a low entropy accretion disk wind scenario and demonstrate how the method may be used to the learn which astrophysical conditions are consistent with both observational and experimental data. Uncertainties in the astrophysical conditions also make it difficult to know if merger events are responsible for populating the heaviest observed nuclei, the actinides. Here I will discuss a potential direct signature of actinide production in merger environments which would confirm mergers capable of being a dominant source of r-process material in the galaxy. However, an r-process which reaches the actinides is also likely to host fission, which is largely experimentally uncharted for neutron-rich nuclei. The influence of fission on lanthanide abundances, and the potential for future experimental and theoretical efforts to refine our knowledge of fission in the r-process, will be discussed. The question of where nature primarily produces the heavy elements can only be answered through such collaborative efforts between experiment, theory, and observation.

Theorie-Seminar

Ingo Tews (INT)
How well does GW170817 constrain the equation of state of dense matter?

Neutron stars are astrophysical objects of extremes. They contain the largest reservoirs of degenerate fermions, reaching the highest densities we can observe in the cosmos. In August 2017, the first neutron-star merger, GW170817, has been observed, which provided compelling evidence that these events are an important site for the production of neutron-rich heavy elements within the r-process.
In addition, GW170817 provides constraints on the tidal polarizability of neutron stars, which describes how a star deforms under an external gravitational field. The tidal polarizability strongly depends on the radius and, therefore, GW170817 has been used to constrain the mass-radius relationship of neutron stars.

In this talk I will use Chiral effective field theory (EFT) and advanced Quantum Monte Carlo (QMC) many-body methods to predict the tidal polarizability of GW170817 from state-of-the-art calculations of the equation of state. I will use two different high-density extrapolations and answer the question how well GW170817 constrains the EOS of dense matter.

Theorie-Seminar

Dean Lee (Michigan State University)
Recent results and future directions in nuclear lattice simulations

I discuss several recent developments and ongoing work in nuclear lattice simulations. The topics include improved chiral interactions on the lattice, eigenvector continuation, superfluid pairing in neutron matter, and the pinhole algorithm for nuclear structure and thermodynamics.

Theorie-Seminar

Ulrich Heinz (The Ohio State University)
How the heck is it possible that a system emitting only a dozen particles can be described by fluid dynamics?

The "unreasonable effectiveness" of relativistic fluid dynamics in describing high energy heavy-ion and even proton-proton collisions will be demonstrated and discussed. Several recent ideas of optimizing relativistic fluid dynamics for the specific challenges posed by such collisions will be presented, and some thoughts will be offered why the framework works better than originally expected. I will also address the unresolved question where exactly hydrodynamics breaks down, and why.

Theorie-Seminar

Javier Redondo (Zaragoza and MPI Munich)
Formation of axion miniclusters

If the dark matter is made of axions and the Peccei-Quinn symmetry is restored after inflation, the distribution of dark matter becomes highly inhomogeneous at scales below a few milli-parsec. In such scenario, a sizeable part of the dark matter becomes bounded gravitationally in tiny dark matter halos, called axion mini-clusters. We are studying the formation of axion mini clusters starting from the initial density distribution predicted by numerical simulations in the early Universe until shortly after matter-radiation equality. This allows to predict the abundance and properties of these halos and their phenomenological implications. In this talk we will review the phenomenology of this very exciting and predictive scenario, our first results and, time-permitting, an overview of the experimental approaches to detect axion dark matter in this scenario.

Theorie-Seminar

Benoit Cote (Konkoly Observatory, Hungary)
Chemical Evolution of Galaxies. From Nuclear Astrophysics to Cosmological Structure Formation

Galactic chemical evolution (GCE) is a multidisciplinary topic that involves nuclear physics, stellar evolution, galaxy evolution, and cosmology. Observations, experiments, and theories need to work together in order to build a comprehensive understanding of how the chemical elements synthesized in astronomical events are spread inside and around galaxies and recycled into new generations of stars. In this talk, I will present our efforts to create permanent connections between the different fields of research involved in GCE, highlight the impact of nuclear physics uncertainties on GCE predictions, and describe the challenges of using chemical abundances to trace the formation and evolution of dwarf galaxies in the early universe. I will also discuss the implication of the first gravitational wave detection of a neutron star merger event (GW170817, Abbott et al. 2017) on the evolution of r-process elements in the Milky Way, and present some of the future challenges that need to be addressed in the quest of identifying the main r-process site in the universe.

Theorie-Seminar

Hilla De-Leon (University of Jerusalem)
Solar pp-fusion rate and electroweak interactions

The main source of energy generated in the Sun is a set of exothermic reactions (named the pp chain) in which 4 protons are fused into 4He. The first and the slowest reaction of this set is the pp fusion, which is a two-nucleon weak reaction that fuses two protons into deuteron and determines the Sun's lifetime. However, due to its long lifetime it cannot be measured, so its rate, which is proportional to the matrix element squared of the weak interaction between initial and final nuclear states, has to be estimated from theory only.

In our theoretical work we predict the pp fusion by using a method named pion-less Effective Field Theory in which the corresponding coupling constants are fixed from a different weak decay, (named triton beta-decay) by using the universality and the consistency of chiral EFT in the transition between one, two and three nucleon electroweak reactions. In addition, this universality reveals that our prediction for the pp fusion rate highly depends on recent new measurements of the neutron half-life.

Theorie-Seminar

Pierre Athuis (Saclay)
Bogoliubov Many-Body Perturbation Theory for Open-Shell Nuclei

In the recent years, ab initio methods have known a resurgence of interest among the nuclear theory community. Recent investigations [Tichai et al., 2016] have shown that Many-Body Perturbation Theory (MBPT), when using Hamiltonians evolved through the Similarity Renormalization Group method, could provide results competing with more demanding techniques like Self-Consistent Green's Functions or Coupled-Cluster.

Recent efforts have been made to extend this formalism to Bogoliubov reference state that break the symmetry associated with the particle number [Duguet and Signoracci, 2017]. We will here present the BMBPT formalism as well as its extension to higher orders through automated methods and first numerical results.

Theorie-Seminar

Astrid Eichhorn (Heidelberg)
An asymptotically safe link between the Planck scale and the eletroweak scale

I will discuss the asymptotic-safety paradigm as a framework for model of quantum gravity and matter at and beyond the Planck scale. I will highlight indications for the theoretical viability of this scenario and discuss how in this setting, Planck-scale physics could lead to testable consequences at the electroweak scale. In particular, the asymptotic-safety paradigm could have a higher predictive power than the Standard Model, and thus the values of free parameters of the Standard Model, such as, e.g., the values of the Abelian gauge coupling, the Higgs mass, as well as the Yukawa couplings of the heavy quarks, could be fixed uniquely by demanding asymptotic safety at the Planck scale.

Theorie-Seminar

Akaki Rusetsky (Uni Bonn)
Three-particle dynamics on the lattice

A detailed review of the general framework, which enables one to extract the bound-state and scattering observables in the three-particle sector from the measured three-particle energy spectrum on the lattice, is given. The framework is based on the particle-dimer formulation of the non-relativistic effective theory in a finite volume. In particular, the absence of the off-shell effects in the finite volume spectrum and the finite-volume shift of the three-particle bound state energy are discussed. Further, it is explicitly shown that, taking into account the cubic symmetry on the lattice, the three-particle quantization condition can be block-diagonalized, where the blocks correspond to the different irreducible representations of the octahedral group.

Theorie-Seminar

Joaquin Drut (UNC)
Signal-to-noise issues in non-relativistic quantum matter: from entanglement to thermodynamics

Non-relativistic quantum matter, as realized in ultracold atomic gases, continues to be a remarkably versatile playground for many-body physics. Experimentalists have exquisite control over temperature, density, coupling, and shape of the trapping potential. Additionally, a wide range of properties can be measured: from simple ones like equations of state to more involved ones like the bulk viscosity and entanglement. The latter has received much attention due to its connection to quantum phase transitions, but it has proven extremely difficult to compute: stochastic methods display exponential signal-to-noise issues of a very similar nature as those due to the infamous sign problem affecting finite-density QCD. In this talk, I will present an algorithm that solves the signal-to-noise issue for entanglement, and I will show results for strongly interacting systems in three spatial dimensions that are the first of their kind. I will also present a few recent explorations of the thermodynamics of polarized matter and other cases that usually have a sign problem, using complexified stochastic quantization.

Theorie-Seminar

Jacopo Ghiglieri (CERN)
Sterile neutrino production in the early universe

The addition of sterile, massive right-handed neutrinos to the Standard Model represents an economical extension with the potential of accounting for three SM shortcomings: the active (left-handed) neutrino masses and oscillations, the matter-antimatter imbalance of the universe and the nature of Dark Matter. I will start by introducing the model and reviewing the basics of the mechanisms responsible for masses, baryogenesis and DM, i.e. see-saw, leptogenesis and resonant production of keV-scale right-handed neutrinos respectively. I will then concentrate on two related ingredients for computations of leptogenesis and or/dark matter: the right-handed neutrino production rate and the lepton asymmetry washout rate, and show how they can be computed, extending to early universe cosmology techniques devised for the QCD plasma in heavy ion physics.

Theorie-Seminar

Sota Yoshida (University of Tokyo)
Shell-model interactions with chiral NN and NNN forces

The derivation of shell-model effective Hamiltonian from chiral nuclear forces based on various ways, MBPT, IM-SRG, and CC, is one of the hottest topics in nuclear structure physics. I will show the various uncertainties of shell-model interactions derived from chiral NN and 3N forces. I will discuss, in particular, the difference between ones by valence IM-SRG and MBPT and the uncertainties due to the treatment of three-body forces, then show my some results for pf-shell nuclei.

Theorie-Seminar

Tim Harris (Helmholtz Institut Mainz)
Toward an estimate of the thermal photon production rate from lattice QCD

In this talk I will describe a new calculation of the thermal production
rate of photons from a QCD medium using numerical lattice field theory.
The production rates of weakly-interacting particles from strongly-interacting mediums are important to understand heavy-ion collisions and the early universe. I will review some of the challenges in quantifying real-time phenomena from lattice QCD and present a key observation which gives us better control over the systematic uncertainties in this particular case. Then I will describe some details of this first computation in full non-perturbative QCD and compare to results using other approaches. Finally, I will present the outlook for improvements to the photon rate computation and discuss lessons which can be learned for similar observables.

Theorie-Seminar

Lennart Dabelow (Uni Jena)
Momentum-dependent four-fermion interactions

Using functional renormalization group methods, we investigate (2+1)-dimensional relativistic fermion systems with momentum-dependent couplings, which serve as effective theories in condensed matter or as toy models for high-energy physics. While derivative expansions of such models with pointlike interactions have been studied extensively in the literature, little is known about the vertex functions' momentum dependence. After a general analysis of momentum-dependent flow equations, we work out dominant interaction channels and determine renormalization group fixed points and critical exponents of Gross-Neveu- and Thirring-type models using pseudospectral methods. In the limit of infinite flavor number, we can even derive an analytic solution. Finally, we compare our findings to previous results obtained by different approaches.

Theorie-Seminar

Tono Coello (TU Darmstadt)
Study of beta and two-neutrino double-beta decays within an effective theory for collective nuclei

We studied beta decays within an effective theory that treats nuclei near the shell closures as a spherical collective core with an even number of neutrons and protons coupled to an additional neutron and/or proton. We start exploring Gamow-Teller beta decays of parent odd-odd nuclei into the ground-, one-, and two-phonon states of the daughter even-even system. The theoretical uncertainty for the matrix elements associated to these decays is estimated based on the power counting of the effective theory. For a variety of medium-mass and heavy isotopes, the theoretical matrix elements are in good agreement with experiment within the theoretical uncertainties. We then study the two-neutrino double-beta decay into ground states. Our results are also consistent with experiment within theoretical uncertainties, without the necessity to further adjust low-energy constants.

Theorie-Seminar

George Bertsch (INT)
Shapes of Nuclei

Coexistence of different shapes is an old subject that advanced greatly in
some respects but not others. We now have a very good picture of the
potential energy surface in heavy nuclei but the interactions required
for shape dynamics are still not well characterized. It is worth recalling
the early studies on light nuclei which were rather successful in describing shape mixing. Perhaps a new approach in the spirit of the old calculations could explain phenomena that current theory does not model well.

Theorie-Seminar

Corbinian Wellenhofer (TU Muenchen)
Isospin-Asymmetry Dependence of the Thermodynamic Nuclear Equation of State

The equation of state (EoS) of hot and dense neutron-rich nuclear matter is an essential quantity in nuclear astrophysics and governs the properties of neutron stars and core-collapse supernovae. In this talk, we discuss computations of the thermodynamic nuclear EoS in many-body perturbation theory (MBPT) using nuclear two- and three-body interactions derived from chiral effective field theory. We show that the proper generalization of MBPT to finite temperatures amounts to a nontrivial reorganization of the standard linked-cluster expansion for the free energy in terms of a Legendre transformation of truncated correlation functions. Using this framework, we then investigate in detail the isospin-asymmetry dependence of the EoS at different densities and temperatures. Finally, we discuss future research efforts that are headed towards the construction of a chiral nuclear EoS for astrophysical applications.

Theorie-Seminar

Joerg Jaeckel (Uni Heidelberg)
WISPy Dark Matter

Very light bosons, produced non-thermally in the early Universe are an intriguing possibility for the cold dark matter of the Universe. Particularly interesting candidates are axions, axion-like particles and hidden photons. This talk will discuss the current status of such light dark matter with a particular emphasis towards opportunities for its detection. We also venture to some more exotic candidates and motivations.

Theorie-Seminar

Jonas Lippuner (Caltech)
The origin of heavy elements: r-process nucleosynthesis in neutron star mergers

The Big Bang produced mostly hydrogen and helium. Nuclear fusion in
stars produces elements up to iron and supernovae create iron peak
elements (A ~ 56). Most of the remaining heavier elements are
produced by neutron capture. In this talk, I will discuss the origin
of the elements with an emphasis on heavy elements. I will give an
overview of the slow and rapid neutron capture processes (s- and
r-process) and I will briefly address the open question of the
r-process site. I will then describe recent nucleosynthesis results
I have obtained with my reaction network code SkyNet. Those results
focus on neutron star mergers, which seem to be the most promising
site for the r-process. Finally, if time permits, I will discuss the
potential optical counterparts of r-process nucleosynthesis events,
called kilonovae.

Theorie-Seminar

Daniel Robaina (TU Darmstadt)
Finite temperature aspects of Lattice gauge theories

I will discuss some aspects of finite temperature calculations of Lattice gauge theories. First, I will focus on boundary effects and show how these can be used to our advantage. In particular, I will present the
concept of shifted boundary conditions within SU(3) Yang-Mills theory. Secondly, I will consider Nf = 2 QCD at nite temperature below the phase transition and study a modified dispersion relation for the
pion quasiparticle. I will show that a massless pseudoscalar excitation would travel through the medium slower than the speed of light by a factor u(T) which is only a function of temperature and is called the
`pion velocity'. Some implications for the Hadron Resonance Gas Model (HRG) can be drawn.

Theorie-Seminar

Sarah Wesolowski (Ohio State University)
Uncertainty quantification in chiral effective field theory

Theorie-Seminar

Ralf-Arno Tripolt (ECT* Trento)

The RVP method in principle allows to obtain the analytic continuation of a function given in numerical form. It only requires real input in order to reconstruct the underlying function not only along the real axis but also in the complex plane. It is applied to experimental data in order to locate complex resonance poles as well as decay thresholds. Moreover, it is applied to numerical data on a Euclidean (imaginary-time) propagator in order to obtain the real-time propagator and the corresponding spectral function in momentum space. This procedure in principle represents an alternative to techniques like the Maximum Entropy Method (MEM) and to inverting the associated Laplace transform. (https://arxiv.org/abs/1610.03252)

Theorie-Seminar

Thomas Duguet (CEA, Saclay)
Using symmetry breaking (and possible restoration) in ab initio nuclear many-body calculations

I will elaborate on the recent progress of ab initio nuclear many-body calculations focusing on the benefit of exploiting the concept of symmetry breaking (and subsequent restoration) to tackle open-shell systems. I will briefly review various recent formal developpements as well as recent and future implementations along this line. In order to illustrate some aspects of the current capacity of ab initio calculations in mid mass nuclei, I will present new results of a systematic study dedicated to the potential "bubble" nucleus 34Si.

Theorie-Seminar

Christian Fischer ()
Spectrum and properties of mesons, baryons and more exotic objects

Theorie-Seminar

Marc Wagner ()
Investigating heavy mesons and tetraquarks with lattice QCD

I give a brief introduction for non-experts, how to compute hadron
masses using lattice QCD. Then I discuss two of our recent projects, (1)
the computation of the low-lying spectra of D mesons, D_s mesons and
charmonium states and (2) the study of possibly existing
heavy-heavy-light-light tetraquarks.

Theorie-Seminar

Boris Carlsson (Chalmers University)
Chiral Effective Field Theory and predictive power

The search for a theoretical understanding of the interaction between nucleons is an ongoing challenge ever since the neutron was discovered in the 1930's. In a modern picture the strong force is a residual force stemming from QCD - the interaction between quarks and gluons. This fact can be incorporated in nucleon interaction models through the use of Chiral Effective Field Theory. Together with a power counting scheme this approach allows for calculations of low-energy two-nucleon, pion-nucleon and few-nucleon observables using the same theoretical framework. Physics that is not included explicitly in the Effective Field Theory is incorporated via a set of low-energy constants that need to be determined by a fit to experimental data. Together with ever improving ab initio many-body methods and increasing computational power, this opens up for precise theoretical predictions with a handle on the accompanying uncertainty.

In this talk I will present pioneering work where simultaneous fits to pion-nucleon and nucleon-nucleon scattering data and bound-state properties for A=2,3 systems have been made for the first time. This is performed up to next-to-next-to-leading order (N2LO) in the chiral expansion, with preliminary results also for the next order, N3LO.

Theorie-Seminar

Michael Wurm (Johannes Gutenberg University Mainz)
The Jiangmen Underground Neutrino Observatory: Flux, form and flavor of a galactic SN neutrino burst

TBA

Theorie-Seminar

Mark Caprio (University of Notre Dame)
Natural orbitals for ab initio calculations

Ab initio calculations of nuclear structure face the challenge of describing a complex multiscale quantum many-body system. The nuclear wave function has both strong short-range correlations and long-range contributions. Natural orbitals provide the means of adapting the single-particle basis for ab initio nuclear no-core configuration interaction (NCCI) calculations to better match the many-body wave function. Natural orbitals are obtained by diagonalizing the one-body density matrix from a calculation using an initial single-particle reference basis, such as the traditional harmonic oscillator basis. A natural orbital basis builds in contributions from high-lying oscillator shells, accelerating convergence of wave functions, energies, and other observables. This talk will provide an introduction to the use of natural orbitals in NCCI calculations. We will explore the convergence of calculated energies, radii, and electromagnetic observables in p-shell nuclei.

Theorie-Seminar

Angelo Calci (TRIUMF)
Continuum and 3N effects in ab initio calculations for p-shell nuclei

The rapid developments to construct divers families of chiral two- (NN) and three-nucleon (3N) interactions and the conceptual and technical improvements of ab initio many-body approaches pose a great opportunity for nuclear physics. The accurate description of the 11Be nucleus, in particular, n+10Be halo structure and the ground-state parity inversion constitutes an enormous challenge for the developments of nuclear forces and many-body approaches. I present a sensitivity analysis of structure and reaction observables to different NN+3N interactions using the ab initio NCSM with continuum (NCSMC). The explicit inclusion of 3N interactions in ab initio reaction calculations is computationally highly demanding and constitutes the current bottle neck for the description of complex nuclear reactions.
I will present an approach to incorporate the normal-ordering approximations in nuclear reaction calculations and demonstrate the reliability of this technique. Due to the drastically reduced computational cost, heavier and more complicated systems can be studied with the NCSMC. As an example I will analyze the p+11C system to demonstrate continuum effects in the complicated 12N spectrum.

Theorie-Seminar

Sven Binder (Oak Ridge National Laboratory)
Effective Field Theory in the Harmonic Oscillator Basis

We develop interactions from chiral effective field theory (EFT) that are tailored to the harmonic oscillator basis. As a consequence, ultraviolet convergence with respect to the model space is implemented by construction and infrared convergence can be achieved by enlarging the model space for the kinetic energy. By fitting to realistic phase shifts and deuteron data we construct an effective interaction from chiral EFT at next-to-leading order. Many-body coupled-cluster calculations of nuclei up to 132Sn exhibit a fast convergence of ground-state energies and radii in feasible model spaces.

Theorie-Seminar

Ke-Jung Chen (National Astronomical Observatory of Japan)
Lighting up the Universe with the First Stars, Supernovae, and Galaxies

One of the paramount problems in modern cosmology is to elucidate how the first generation of luminous objects, stars, supernovae, accreting black holes, and galaxies, shaped the early universe at the end of the cosmic dark ages. According to the modern theory of cosmological structure formation, the hierarchical assembly of dark matter halos provided the gravitational potential wells that allowed gas to form stars and galaxies inside them. Modern large telescopes have pushed the detection of galaxies up to a redshift of z ~ 10. However, models of the first luminous objects still require considerable effort to reach the level of sophistication necessary for meaningful predictions, Due to the complexity of involved physical phenomena, this physical understanding may only come by the proper use of numerical simulations. Therefore, I have used state-of-the-art simulations on some of largest supercomputers to study these objects. In my talk, I will discuss the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also give possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).

Theorie-Seminar

Mirko Miorelli (TRIUMF)
Dipole strength from first principles calculations

The electric dipole polarizability quantifies the low-energy behavior of the dipole strength. It is related to the proton and neutron distributions of the nucleus, and thereby can be used to constrain the neutron equation of state and the physics of neutron stars. Only recently however, new developments in ab initio methods finally allowed first principles studies of the dipole strength in medium-mass nuclei [1,2,3]. Using the Lorentz integral transform coupled cluster method with the newly developed chiral interaction at next-to-next-to-leading order (NNLO_sat) we study the low energy behavior of the dipole strength in 4He, 16O, 22O [3] and 48Ca for which the polarizability has been recently measured by the Osaka-Darmstadt collaboration. For the exotic 22O we observe large contribution to the dipole strength at very low energy, indicating the presence of a pygmy dipole resonance, in agreement with what experimentally found by Leistenschneider et al.[4]. Finally, I will show preliminary calculations on the exotic 8He, which exhibits extremely large dipole polarizability and neutron skin.

[1] S. Bacca, N. Barnea, G. Hagen, G. Orlandini, and T. Papenbrock, Phys. Rev. Lett. 111, 122502 (2013)
[2] S. Bacca, N. Barnea, G. Hagen, M. Miorelli, G. Orlandini, and T. Papenbrock, Phys. Rev. C 90, 064619 (2014)
[3] M. Miorelli, S. Bacca, N. Barnea, G. Hagen, G. R. Jansen, G. Orlandini, and T. Papenbrock, arXiv:1604.05381 (2016)
[4] A. Leistenschneider et al., Phys. Rev. Lett. 86, 5442 (2001)

Theorie-Seminar

Alan A. Dzhioev (JINR, Dubna)
QRPA with Skyrme interactions and supernova neutral-current neutrino-nucleus reactions

The significant role played by processes with neutrinos in core-collapse supernovae is well known. At densities of rho > 10^11 g cm^-3 neutrino interactions with matter become important, leading to neutrino trapping and thermalization. Moreover, neutrino energy deposition behind the stalled shock may play a crucial role in successful explosion.

We study thermal effects on the cross sections and rates for neutral-current neutrino-nucleus reactions occurring under supernova conditions. The approach we use is based on the thermal quasiparticle random phase approximation combined with the Skyrme energy density functional method (Skyrme-TQRPA). The approach enables self-consistent studies of neutrino reactions with hot nuclei in a thermodynamically consistent way, i.e., without assuming the Brink hypothesis and without violation the detailed balance principle. For the sample nuclei, 56Fe and 82Ge, the Skyrme-TQRPA is applied to analyze thermal effects on the strength function of charge-neutral Gamow-Teller transitions which dominate neutrino-nucleus reactions at E_nu < 20 MeV. For the relevant supernova temperatures, we calculate cross sections for neutrino inelastic scattering. The results are compared to those obtained from large-scale shell-model calculations and possible reasons for the observed discrepancy are discussed. We also apply the method to examine the process of neutrino-antineutrino pair emission by hot nuclei.

Theorie-Seminar

Martin Obergaulinger (Universidad de Valencia)
Core collapse in high-mass stars with rotation and magnetic fields

Across the wide range of possible progenitors, supernova core collapse
may lead to very different evolutionary outcomes, in particular if
rotation and magnetic fields are taken into account. In particular for
stars in the upper mass range of SN progenitors, I will present results
of neutrino-MHD simulations where different combinations of physical
effects give rise to different kinds of successful and failed explosions.

Theorie-Seminar

Irene Tamborra (Niels Bohr Institute)
Neutrinos: Messengers of the core-collapse physics

Neutrinos are key particles in core-collapse supernovae. Neutrinos can be direct probes of the still uncertain and fascinating supernova mechanism. Intriguing recent developments on the role of neutrinos during the stellar collapse are reviewed, as well as our current understanding of the flavor conversions in the stellar envelope. The detection perspectives of the next burst will be also outlined.

Theorie-Seminar

Ingo Tews (Institute for Nuclear Theory, Seattle)
Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties

Theorie-Seminar

Lucas Platter (University of Tennessee)
Effective field theory for Halo Nuclei

Halo nuclei are weakly bound nuclei whose degrees of freedom are a
tightly bound core and a small number of valence nucleons. These systems
are of experimental interest since they are important in reactions
relevant to nuclear astrophysics but also since they frequently occur
close to the neutron dripline. I will discuss the application of
effective field theory to these weakly bound nuclei and provide a number
of examples where this approach leads to new information.

Theorie-Seminar

Takami Kuroda (Uni Basel)
Toward multi messenger astronomy in CCSN: coherent emissions of gravitational-waves and neutrinos from non-rotating progenitor star

Theorie-Seminar

Hermann Krebs ()
Nuclear forces and currents in chiral effective field theory

Nuclear forces and currents serve as an input for various many-body calculations of nuclear spectra and scattering processes. Their quantitative description without losing the connection to QCD is provided by a powerful tool like chiral effective field theory. In my talk I will discuss the current status of their construction and their ongoing implementations. In particular I will present our results on two-nucleon axial vector current upto leading one-loop order in chiral expansion which is consistent with already developed N3LO nuclear forces, is renormalizable and behaves as a four vector under Lorentz transformation. Due to upsense of short-range low energy constants at this order the current has high predictive power.

Theorie-Seminar

Christian Forssen (Chalmers University)
Theoretical uncertainty quantification and precision nuclear physics

Ab initio nuclear models are required for a truly predictive theory of nuclei and their interactions with external probes. However, true predictive power requires the ability to quantify theoretical uncertainties. While it is true that theoretical error estimates are difficult to obtain, the pursuit thereof plays a pivotal role in science. Reliable theoretical errors can help to determine to what extent a disagreement between experiment and theory hints at new physics, and they can provide input to identify the most relevant new experiments. As will be shown, nuclear theory has reached a stage where such questions can be addressed.

Theorie-Seminar

Michael Urban (IPN Orsay)
Superfluid hydrodynamics in the inner crust of neutron stars

In the inner crust of neutron stars, nuclei (clusters) are immersed in a dilute gas of unbound neutrons. At the typical temperatures of neutron stars, the neutrons are superfluid and the most important excitations are therefore phase fluctuations of the gap (Goldstone mode or Bogoliubov-Anderson sound). In the first part of the talk, I will discuss the Goldstone mode in uniform neutron matter and its contribution to the specific heat obtained within the Quasiparticle Random-Phase Approximation (QRPA) and compare it with results of simple superfluid hydrodynamics. In the second part, the hydrodynamic approach will be applied to the inhomogeneous crust (crystalline and pasta phases) to calculate the effective mass of the clusters and the density of superfluid neutrons. Consequences for the interpretation of glitch data will be discussed.

Theorie-Seminar

Micaela Oertel (LUTH, CNRS/Observatoire de Paris, Meudon)
On the maximum mass of magnetised white dwarfs

To explain observations of overluminous Type Ia supernovae, strongly magnetized super-Chandrasekhar mass white dwarfs have been proposed as their progenitors. This has interesting implications in high-precision cosmology, as Type Ia supernovae have been widely used as standard candles. To compute equilibrium configurations of magnetized white dwarfs, we apply our recently developed self-consistent formalism for modelling the macroscopic structure of a compact object in strong magnetic fields. In previous attempts to determine the mass-radius relation of magnetized white dwarfs, there has been no study which simultaneously included Landau quantization of electrons in a strong magnetic field, electron-ion interactions and effects of pressure anisotropy due to the breaking of spherical symmetry by the background magnetic field. In addition to a self-consistent modelling of the structure of a white dwarf in strong magnetic fields in full general relativity, we perform a systematic study of its stability which ultimately decides whether such objects can exist in nature. We confirm previous speculations that indeed the onset of electron captures and pycnonuclear reactions limit the stability of strongly magnetized white dwarfs and hence they cannot explain the observations of overluminous supernovae.

Theorie-Seminar

Edmond Iancu (IPhT - CEA)
Jet evolution in a dense QCD medium: wave turbulence and thermalization

For an energetic jet propagating through a weakly-coupled quark-gluon plasma, I present the physical picture of jet quenching, as emerging from the interplay between multiple branchings and elastic collisions. The medium-induced branchings are quasi-democratic and lead to a phenomenon of wave turbulence, which ensures the efficient transmission of the energy from the leading particle to a myriad of soft particles. The elastic collisions are responsible for the momentum broadening and the thermalization of the soft branching products. This first-principle picture provides a natural explanation for the phenomenon of di-jet asymmetry observed in Pb+Pb collisions at the LHC.

Theorie-Seminar

Samuel Jones (University of Victoria)
Simulating the lives and deaths of 8-10 solar-mass stars

Theorie-Seminar

Vittorio Soma (CEA Saclay)
Properties of medium-mass nuclei and ab initio strategy

After several developments in terms of many-body techniques have pushed ab initio nuclear structure calculations to cover a good fraction of existing mid-mass nuclei, recently the focus of practitioners has moved back to the input nuclear Hamiltonian. Employing one of such many-body techniques, namely self-consistent Green functions, and different state-of-the-art two- and three-nucleon interactions, I will discuss novel ab initio results for oxygen, potassium, calcium and nickel isotopic chains. Particular attention will be dedicated to the performance of a newly developed interaction, NNLOsat. In the case of oxygens I will also present a new re-evaluation of matter radii that complements well-known energy systematics.

Theorie-Seminar

Riccardo Ciolfi (University of Trento)
Electromagnetic counterparts of BNS mergers: the case of long-lived NS remnants

Recent observations indicate that in a large fraction of binary neutron star (BNS) mergers a long-lived neutron star (NS) may be formed rather than a black hole. Unambiguous electromagnetic (EM) signatures of such a scenario would strongly impact our knowledge on how short gamma-ray bursts (SGRBs) and their afterglow radiation are generated. Furthermore, such EM signals would have profound implications for multimessenger astronomy with joint EM and gravitational-wave (GW) observations of BNS mergers, which will soon become reality with the first science runs of the advanced LIGO/Virgo network of ground-based GW detectors already on the way. I will discuss various aspects of BNS mergers leading to the formation of a long-lived NS, including the scenarios that relate such mergers to SGRBs. Moreover, I will introduce a new model to follow the post-merger evolution of the system and to predict in a self-consistent way the (X-ray) emission powered by the NS spindown. I will present the computed lightcurves and spectra and discuss these results in the context of SGRBs and multimessenger astronomy.

Theorie-Seminar

William J. Porter (UNC, Chapel Hill)
Toward Unitary Entanglement

Studying entanglement in many-body quantum systems is an active and exciting area of research with several key quantities only recently becoming experimentally accessible. In my talk, I will discuss the basic definition for and some lattice Monte Carlo approaches to computing the Renyi entanglement entropies for strongly interacting fermions. With the introduction of an auxiliary parameter, a well-known signal-to-noise problem can be circumvented, and the Renyi entropies can be computed using auxiliary field Monte Carlo methods. After presenting proof-of-principle results for small systems, I will comment on my progress toward characterizing universal entanglement properties of the scale-invariant Fermi gas.

Theorie-Seminar

Akaki Rusetsky (University of Bonn)
Scattering processes on the lattice

I review the use of the effective field theory methods in a finite volume for the study of hadron-hadron scattering processes on the lattice. For illustration of the general approach, two examples are given. We first consider inelastic scattering processes and show that one can directly extract the scattering phase and the inelasticity parameter on the lattice without studying scattering into all open channels separately. The approach is applicable even in the presence of the multi-particle (three and more) inelastic channels. Next, an explicit expression for the energy-level shift of a shallow bound state of three identical particles in a finite volume is derived. It is demonstrated that measuring the volume-dependence of the spectrum of the bound states provides one with an important information about their nature.

Theorie-Seminar

(University of Tennessee)
Effective field theory approach to collective motion in heavy atomic nuclei

Previously, collective motion in heavy nuclei has been studied within collective and algebraic models. While they reproduce the energy spectra of these systems, their predictions for electromagnetic transitions and moments are in disagreement with experimental data. An effective field theory approach to collective motion in heavy nuclei solves this long-standing problem. The systematic construction of the theory allows for the estimation of theoretical uncertainties. Bayesian methods can be employed to quantify these uncertainties, providing a clear statistical interpretation. Experimental data is consistent with the theory within theoretical uncertainties. The systematic construction of the electric quadrupole operator allows for the description of faint interband transitions strengths in rotational nuclei and large static quadrupole moments in vibrational nuclei near shell closures.

Theorie-Seminar

Cristina Volpe (APC, Paris)
tba

Theorie-Seminar

Dario Vretenar (University of Zagreb)
Evolution of Low-Energy Nuclear Collective Excitations

Low-energy collective excitations reflect the underlying effective nuclear interactions and shell structure of single-nucleon orbitals. The evolution of collective states characterizes a variety of interesting structure phenomena across the nuclide chart: clustering in light nuclei, modification of shell structures and occurrence of deformations, location of the drip-line in neutron-rich nuclei, shape coexistence and shape transitions in medium heavy and heavy nuclei, low-energy resonances, octupole correlations, subshell closures in superheavy nuclei, etc.

The microscopic self-consistent mean-field method that uses effective interactions or energy density functionals, provides a complete and accurate description of ground-state properties and collective excitations, from relatively light systems to superheavy nuclei, and from the valley of beta-stability to the particle drip-lines. Based on this framework, structure models have been developed that go beyond the static mean-field approximation and include collective correlations related to restoration of broken symmetries and fluctuations of collective variables. These models have become standard tools for nuclear structure calculations, able to describe a wealth of new data and predict low-energy nuclear phenomena.

Theorie-Seminar

Sean M. Couch (MSU)
Simulations of Supernovae and Their Massive Star Progenitors in 3D

Core-collapse supernovae are the luminous explosions that herald the death of massive stars. While core-collapse supernovae are observed on a daily basis in nature, the details of the mechanism that reverses stellar collapse and drives these explosions remain unclear. While the most recent high-fidelity simulations show promise at explaining the explosion mechanism, there remains tension between theory and observation. This is likely telling us we are missing important physics in our simulations. I will discuss some interesting candidates for such missing physics that could be crucial to the supernova mechanism. In particular, I will describe our efforts to develop more realistic initial conditions for supernova simulations with fully 3D massive stellar evolution calculations. Such realistic 3D initial conditions turn out to be favorable for successful explosions, in large part because they result in stronger turbulence behind the stalled supernova shock. I will also discuss the important role turbulence is playing in the supernova mechanism and what might be required for accurately modeling the turbulence in our simulations.

Theorie-Seminar

Mirko Miorelli (TRIUMF)
Electromagnetic observables from coupled cluster theory

The study of electromagnetic break-up reactions with nuclei is of fundamental importance to understand nuclear dynamics. In particular, ab initio approaches are crucial to connect nuclear physics with the more fundamental QCD regime. Until very recently, most of the ab initio calculations of such reactions where the nucleus is broken in several pieces, were restricted to very light nuclei (A<=7). I will show how the coupled-cluster method and the Lorentz integral transform are combined for the computation of inelastic reactions into the continuum for medium-mass nuclei [1]. I will discuss results for the photo-absorption cross section for a variety of nuclei, in particular for the neutron rich 22O nucleus where we find a low-lying E1 strength which compares fairly well with experimental data from GSI [2]. I will then focus on the calculation of the electric dipole polarizability showing results for 4He, 16O and 40Ca. Exploring the correlation between the electric dipole polarizability and the charge radius I will show how we make predictions for the electric dipole polarizability of Ca48 [3] and Ni68.

[1] S. Bacca, N. Barnea, G. Hagen, M. Miorelli, G. Orlandini, T. Papenbrock, Phys. Rev. C 90, 064619 (2014)
[2] A. Leistenschneider et al., Phys. Rev. Lett. 86, 5442 (2001)
[3] G. Hagen, A. Ekstroem, C. Forssen, G. R. Jansen, W. Nazarewicz, T. Papenbrock, K. A. Wendt, S. Bacca, N. Barnea, B. Carlsson, C. Drischler, K. Hebeler, M. Hjorth-Jensen, M. Miorelli, G. Orlandini, A. Schwenk, and J. Simonis, Nat. Phys. 3529 (2015)

Theorie-Seminar

Jacobo Ruiz de Elvira (Bonn University)
Roy-Steiner-equation analysis of pion-nucleon scattering

A precise understanding of low-energy pion-nucleon interactions is central for many areas in nuclear and hadronic physics, ranging from the scalar couplings of the nucleon to the long-range part of two-pion-exchange potentials and three-nucleon forces in Chiral Effective Field Theory. We present a calculation that combines the general principles of analyticity, unitarity, and crossing symmetry with modern high-precision data of hadronic atoms, leading to a phenomenological description of the pion-nucleon amplitude with unprecedented rigor and accuracy. Consequences for the pion-nucleon sigma-term and the matching to Chiral Perturbation Theory will be discussed.

Theorie-Seminar

Raju Venugopalan (BNL/Heidelberg)
Using high energy DIS to probe novel features of short range nucleon-nucleon correlations

A future Electron-Ion Collider will have about 1000 times the luminosity of HERA and can be used to study the short distance properties of (polarized) light and heavy nuclei. We outline a specific measurement which illustrates the potential of such a machine to uncover the quark and gluon nature of short range nucleon-nucleon interactions.

Theorie-Seminar

Yudai Suwa (Kyoto University)
From supernovae to neutron stars

A core-collapse supernovae is a generation site of a neutron star as well as one of the largest explosions in the universe. In this talk, I will show our recent results with multi-dimensional neutrino-radiation hydrodynamics simulations, especially focusing on neutron star formation.

Theorie-Seminar

Jesus Casal (Universidad de Sevilla)
Three-body systems in nuclear reactions and their astrophysical implications

Over the last decades, the advances in radioactive ion beam facilicies have expanded our knowledge of nuclear physics. The structure of weakly-bound and exotic nuclei near the neutron and proton driplines have motivated comprehensive theoretical studies and experimental efforts. In particular, several interesing features, such as few-body structures, clusterization or nuclear halos, have been observed for weakly-bound light nuclei. The case of three-body systems (such as 6He, 9Be, 11Li or 17Ne) and their implications in nuclear reactions and nucleosynthesis processes will be discussed.

From the theoretical point of view, the description of weakly-bound system requires to include the coupling to scattering or continuum states. This is not an easy task, especially for three-body systems. A general method to treat three-body bound and continuum states will be introduced. Then, the method will be applied to describe radiative capture reactions, low-energy direct reactions and quasifree knockout reactions.

Theorie-Seminar

Heiko Hergert (NSCL/ Michigan State University)
Open-Shell Nuclei From First Principles

Nowadays, advances in many-body theories and their numerical implementation have made it possible to routinely calculate properties of nuclei in the mass A~100 region from first principles. The In-Medium Similarity Renormalization Group (IM-SRG), in particular, provides access to open-shell nuclei, either directly or through the auxiliary step of deriving valence-space interactions for use with existing Shell Model technology.
I will give a pedagogical overview of the method and its current capabilities, discuss highlights in the description of ground-state properties and spectra based on chiral two- and three-nucleon interactions, and preview upcoming developments like the construction of consistent transition operators.

Theorie-Seminar

Alexander Heger (Monash Centre for Astrophysics, Monash University, Australia)
The Making of the First Heavy Elements

The first stars are unique not only in being first but also because of
being first, they have a unique and pristine primordial initial
composition, which can dramatically alter both their evolution, the
way they die as supernovae, and their resulting nucleosynthesis. For
example, the recently discovered most iron-poor star known,
SM0313-6708, hints at some primordial production process of calcium
that can only be found and seen in such pristine stars. Another
example is that reduced mass loss and higher characteristic initial
masses may lead to a population of pair instability supernovae that
could produce a very unique abundance pattern.

No direct observations of these stars are possible at this time,
however, so our ability to study these early stars is limited to
indirect measurements and numerical simulations, though possibly we
might be able to observe some of their stellar deaths in the near
future. Stellar forensics based on nucleosynthesis patterns preserved
in subsequent generations of stars may be used to attempt
reconstruction of the properties of these first stars. But in order
to be able to use this tool, we need know what abundances were
synthesised in these first generations of stars.

Theorie-Seminar

Noemi Rocco ()
The role of meson exchange currents in neutrino-nucleus interactions: will we solve the axial puzzle?

Theorie-Seminar

Raphael Hix (University of Tennessee)
Multidimensional Simulations of Core-Collapse Supernovae and the Implications for Nucleosynthesis

Core-collapse supernovae (CCSNe), the culmination of massive stellar evolution, are the principle actors in the story of our elemental origins. Though brought back to life by neutrino heating, the development of the supernova is inextricably linked to three-dimensional fluid flows, with large scale hydrodynamic instabilities allowing successful explosions that spherical symmetry would prevent. The importance of the neutrino interactions and the three-dimensional fluid flows that they drive have often been ignored when the nucleosynthesis that occurs in these explosions, and their resulting impact on galactic chemical evo- lution, is discussed. I will present results from simulations of successful explosions using our CHIMERA code, and discuss how the multidimensional character of the explosions directly impacts the development of the explosion as well as the nucleosynthesis and other observables of core-collapse supernovae.

Theorie-Seminar

Norbert Kaiser ()
Single-particle potential from resummed fermionic in-medium ladder diagrams

Theorie-Seminar

Kuo-Chuan Pan (Basel University)
Multi-dimensional core-collapse supernova simulations with the isotropic diffusion source approximation for neutrino transport

The neutrino mechanism of core-collapse supernova is investigated via non-relativistic, multi-dimensional, neutrino radiation-hydrodynamic simulations. For the transport of electron flavor neutrinos, we use the interaction rates defined by Bruenn (1985) in collaboration with the isotropic diffusion source approximation (IDSA) scheme, which decomposes the transported particles into trapped particle and streaming particle components. Heavy neutrinos are described by a leakage scheme. Unlike the "ray-by-ray'' approach in other multi-dimensional IDSA implementations in spherical coordinates, we use 2D cylindrical and 3D Cartesian coordinates and solve the trapped particle component in multiple dimensions, improving the proto-neutron star resolution and the neutrino transport in angular and temporal directions. We perform Newtonian 1D-3D ab initio simulations from prebounce core collapse to several hundred milliseconds postbounce with progenitors from Woosley et al. (2002) with the HS(DD2) equation of state. We obtain robust explosions with diagnostic energies ~0.1-0.5 B for all considered 2D models within approximately 100-300 milliseconds after bounce and find that explosions are mostly dominated by the neutron-driven convection, although standing accretion shock instabilities are observed as well. We also find that the level of electron deleptonization during collapse dramatically affects the postbounce evolution, e.g. the ignorance of neutrino-electron scattering during collapse will leads to a stronger explosion.

Theorie-Seminar

Dr. Pierre Capel ()
From the Coulomb breakup of 15C to the radiative capture 14C(n,gamma)

Coulomb breakup has been proposed as an indirect method to deduce the cross section of radiative captures of astrophysical interest [1]. In Coulomb breakup, the projectile dissociates into lighter fragments through its interaction with a heavy (high Z) target. Assuming the dissociation to be due to the sole Coulomb interaction, the reaction can be described as an exchange of virtual photons between the projectile and the target. It can thus be seen as the time-reversed reaction of the radiative capture of the fragments, which should enable us to deduce easily the radiative-capture cross section from breakup measurements [1].
Using accurate reaction models, various studies have shown that higher-order effects and other reaction artefacts play a significant role in Coulomb breakup, which hinder the simple extraction of radiative-capture cross sections from breakup measurements [2,3]. Nevertheless, a recent analysis shows that accurate calculations of the breakup of 15C on Pb at 70AMeV can be used to deduce the Asymptotic Normalisation Coefficient (ANC) of the 15C bound state from experimental data [4]. This analysis suggests that this ANC can then be used to compute a cross section for the 14C(n,g) radiative capture which is in agreement with direct measurements.
In the present work the influence of the description of the 15C continuum upon breakup calculations is analysed. Interestingly, it is shown to be nearly as significant as that of the ANC. Fortunately, it can be accounted for by fitting the theoretical predictions to the breakup data in the low 14C-n energy range. These results revive the original idea of inferring radiative-capture cross sections from Coulomb breakup measurements.
I will begin this seminar by briefly presenting the Dynamical Eikonal Approximation, the reaction model we use to compute breakup cross sections [5]. I will then detail the results we have obtained in this analysis, emphasizing on the sensitivity of reaction calculations to the projectile description. In addition to its application in nuclear astrophysics, this work also indicates which information of the structure of the projectile actually matters in reaction modelling. This shows how the simple description of nuclei used in accurate reaction codes could be improved from state-of-the-art nuclear-structure models.

[1] G. Baur, C. A. Bertulani, and H. Rebel, Nucl. Phys. A458, 188 (1986).
[2] H. Esbensen, G. F. Bertsch, and K. A. Snover, Phys. Rev. Lett. 94, 042502 (2005).
[3] P. Capel and D. Baye, Phys. Rev. C 71, 044609 (2005).
[4] N. C. Summers and F. M. Nunes, Phys. Rev. C 70, 011602 (2004).
[5] D. Baye, P. Capel, and G. Goldstein, Phys. Rev. Lett. 95, 082502 (2005).

Theorie-Seminar

Panagiota Papakonstantinou (Institute for Basic Science, RISP, South Korea)
Properties and significance of the surface dipole mode

A strong isoscalar dipole transition is known to be excited in a variety of nuclei, including isospin symmetric ones, at approximately 6-7 MeV. A series of theoretical studies and accumulating experimental evidence support an interpretation of the above dipole transition as an elementary surface vibration. Such a mode is potentially as interesting as any collective excitation for a variety of reasons. In addition, though, it is found to account for the observed isoscalar segment of pygmy dipole strength.
In this talk I review related experimental and theoretical results, discuss important implications for pygmy-strength interpretations and searches for genuine neutron-skin oscillations, and touch on the mode's possible role in fusion reactions.

Theorie-Seminar

Andreas Bauswein (Aristotle University of Thessaloniki)
Inferring neutron-star properties from the gravitational-wave signal of binary mergers

TBA

Theorie-Seminar

Andreas Crivellin (CERN Theory Division)
Effective field theory approach to flavour and dark matter

In this talk I review the effective field theory approach to physics
beyond the SM. The effect of new physics can be incorporated in higher
dimensional operators which must respect the SM gauge symmetries. As an application I discuss the effects of dim-6 operators in LFV observables and the determination of the CKM elements from exclusive and inclusive processes. This approach can be easily extended to include DM. Here I discuss the RGE evolution of the effective operators assuming that DM is a SM singlet and correlate direct detection with LHC searches.

Theorie-Seminar

Kyle Wendt (University of Tennessee)
Towards Quantitative Ab Initio Nuclear Structure

Modern ab initio calculations of light and medium mass nuclei have reached a point of unprecedented precision by combining low momentum interactions from chiral effective field theory softened using renormalization group techniques. However, thorough descriptions of uncertainty in such calculations is lacking, both with respect to the many-body method employed and with respect to the systematics of the underlying Hamiltonian. This is exacerbated by many chiral interactions failing to correctly describe medium mass nuclei, often over binding while failing to correctly predict nuclear densities. I will present recent progress in quantifying errors in nuclear Hamiltonians as well as an alternative approach to constraining chiral Hamiltonians such that predictive calculations of light and medium mass nuclei are within reach. I will also present recent developments on understanding certain forms of error that enter into many calculations of light nuclei.

Theorie-Seminar

Owe Philipsen ()
Heavy dense QCD and nuclear matter on the lattice

At finite baryon density the fermion determinant of the QCD partition function is complex-valued. This so-called sign problem
prohibits simulations of lattice QCD by Monte Carlo methods and is the reason that the QCD phase diagram remains largely
unknown. I present a new method to deal with finite densities in two steps. First, an effective lattice theory of Polyakov loops is derived by means of combined strong coupling and hopping expansions. The theory is so far valid for heavy quarks only, but has a milder sign problem that can be dealt with. As an application, the QCD deconfinement transition at finite temperature has been calculated for all baryon densities. Moreover, for the first time it is possible to describe the onset transition to cold nuclear matter at zero temperature as well as the nuclear equation of state and the nuclear binding energy directly from QCD.

Theorie-Seminar

Bruno Giacomazzo (University of Trento)
General Relativistic Simulations of Binary Neutron Star Mergers: Gravitational Waves and Short Gamma-Ray Bursts

In this talk I will present results of fully general relativistic simulations of binary neutron star (BNS) mergers and discuss their connection with current and future astrophysical observations. BNSs are one of the most promising sources of gravitational waves (GWs) that we expect to detect in the next few years with advanced LIGO and Virgo. But they may also emit powerful electromagnetic signals and they are expected to be behind the engine powering short gamma-ray bursts (SGRBs). During the first part of the talk I will discuss the role of BNS merger simulations in predicting the gravitational wave signal emitted during the merger and its connection with the equation of state of NS matter. In the second part I will instead discuss in detail the possible connection between the central engine of SGRBs and the merger of magnetized neutron stars, both in the case in which a black hole is promptly formed after merger and in the case of the formation of a magnetar.

Theorie-Seminar

Juan Torres-Rincon (Subatech, Nantes)
Baryons and their melting temperature in the (P)NJL model

The Nambu-Jona-Lasinio model is an effective theory of QCD for low-energy quark interactions. I will explain how to use this model (and its extension, the Polyakov-NJL model) in combination with the Bethe-Salpeter equation, to describe mesons and diquarks as bound states of quarks + (anti)quarks. In a similar context, baryons can also be modelized as bound states of diquarks + quarks. I will present our results for the baryon masses as a function of temperature and chemical potential, and show a clear evidence of a flavor dependence of the baryon melting temperature, as suggested by experimental results in heavy-ion collisions, and supported by recent lattice-QCD results.

Theorie-Seminar

Hans-Peter Pavel (HU-Berlin and JINR Dubna)
Strong QCD in terms of gauge invariant dynamical variables

Theorie-Seminar

Michael Urban (IPN Orsay)
Anisotropic expansion and collective modes of trapped Fermi gases

Theorie-Seminar

Maxwell T. Hansen (University of Washington)
Multichannel one-to-two transition amplitudes in a finite volume

Numerical Lattice QCD calculations are necessarily performed in a finite volume, and for any given observable it is important to understand this constraint. Over a decade ago Lellouch and Luescher derived a relation between finite-volume matrix elements and observable decay amplitudes for the weak decay K->pi pi. The result is non-trivial, depending not only on the finite volume but also on the phase-shift of pi pi elastic scattering. In this talk we present a generalization of the Lellouch Luescher approach to study one-to-two transition amplitudes. Using a generic relativistic field theory and working to all orders in perturbation theory, we derive a master equation relating finite-volume matrix elements to physical transition amplitudes. Our derivation accommodates external currents which inject momentum, energy and angular momentum into the system. The result is applicable to systems with any number of strongly coupled two-scalar channels, and we illustrate how it can be applied to certain key examples, including heavy meson decays and meson photo production.

Theorie-Seminar

James Lattimer (Stony Brook)
Mass and Radius Constraints for Neutron Stars

Theorie-Seminar

Yang Sun (Shanghai Jiaotong University)
Shell model method for weak interaction rates in heavy, deformed nuclei

Theoretical calculation of nuclear matrix element for Gamow-Teller type transition is important for nuclear structure, nuclear astrophysics, and fundamental physics. It is of particular interest when a laboratory measurement for weak interaction rates is impossible and the conventional shell model calculations are not feasible.

A method for calculation of weak interaction rates has been developed within the frame-work of the Projected Shell Model (PSM) [1,2]. This model is distinguished from conventional shell models by the fact that the PSM uses deformed single particle states to best describe deformed nuclei. The PSM basis is constructed by superimposing angular-momentum-projected multi-quasiparticle configurations, and nuclear wave functions are obtained by diagonalizing two-body interactions in the projected states. In this talk, calculation of transition matrix elements in PSM is discussed in detail, and the effects caused by the Gamow-Teller residual forces and by the configuration-mixing are studied.

With this development, it becomes possible to perform a state-by-state calculation for &#61538;-decay and electron-capture rates in heavy, deformed nuclei at finite temperatures and for both allowed and forbidden transitions. One quantitative example [3] indicates that, while experimentally known Gamow-Teller transition rates from the ground state of the parent nucleus are reproduced, stronger transitions from some low-lying excited states are predicted to occur, which may considerably enhance the total decay rates once these nuclei are exposed to hot stellar environments.


[1] K. Hara and Y. Sun, Int. J. Mod. Phys. E 4, 637 (1995).
[2] Y. Sun and K. Hara, Comp. Phys. Commun. 104, 245 (1997).
[3] Z.-C. Gao, Y. Sun, Y.-S. Chen, Phys. Rev. C 74, 054303 (2006).

Theorie-Seminar

Joel Lynn (Los Alamos National Laboratory)
Progress in Green's function Monte Carlo calculations using chiral EFT interactions

Theorie-Seminar

(The Ohio State University)
UV extrapolations in finite oscillator bases

Theorie-Seminar

Andreas Metz (Temple University)
Transverse single-spin asymmetries: challenges and recent progress

Transverse single-spin asymmetries have been observed in a number of hard scattering processes. While the effects can be quite large, their description in terms of perturbative QCD is challenging. On the other hand, these asymmetries allow us to explore new territories in QCD. In this talk, I briefly review several key aspects of this field and also discuss some recent progress.

Theorie-Seminar

Igor Boettcher ()
Dimensional BCS-BEC Crossover with Ultracold Atoms

Transverse single-spin asymmetries have been observed in a number of hard scattering processes. While the effects can be quite large, their description in terms of perturbative QCD is challenging. On the other hand, these asymmetries allow us to explore new territories in QCD. In this talk, I briefly review several key aspects of this field and also discuss some recent progress. We investigate how the reduction of spatial dimension influences superfluidity of two-component fermions in the BCS-BEC crossover from both a theoretical and an experimental perspective. The Functional Renormalization Group allows to study the system over the whole parameter space of interaction strength, density, temperature, spin-imbalance, and dimension. The high precision and tunability of recent experiments allows for a solid benchmarking of our description. In particular, recent measurements on the 2D BCS-BEC Crossover in the Jochim group at Heidelberg yield major insights into the physics of this system. We present theoretical and experimental results on the equation of state and the phase diagram as a function of dimension.

Theorie-Seminar

Daniel Phillips (Ohio University)
An effective field theory description of halo nuclei

I discuss recent work our group has undertaken on effective-field-theory (EFT) analyses of experimental data pertaining to one- and two-nucleon halos. The cases of Carbon-19 and Lithium-8 (one-neutron halos), Boron-8 (one-proton halo, and Carbon-22 (two-neutron halo) will be discussed. For the one-nucleon halos electromagnetic processes will be discussed (Coulomb dissociation and radiative capture respectively). In the case of Carbon-22 I show how the measured matter radius can be used to derive constraints on the two-neutron separation energy of this very neutron-rich system. If time permits I will also show preliminary results on Coulomb dissociation of this nucleus. In every case I show how the "Halo EFT" correlates different experimental observables with one another, in a model-independent manner, and up to an accuracy that is determined by the separation of scales in the halo system.

Theorie-Seminar

Arianna Carbone (TU Darmstadt)
Correlated density-dependent chiral forces for infinite matter calculations within the Green's function approach

The properties of symmetric nuclear and pure neutron matter are investigated within the self consistent Green's function method. This approach has been recently extended to include the effects of three-body forces. We employ this improved formalism to analyze the effect of many-body forces in the ladder approximation for the study of infinite nuclear matter. The three-body interaction is incorporated by means of a density dependent two-body force. This force is obtained via a correlated average over the third particle, which corresponds to using an in-medium propagator consistent with the many-body calculation we perform. Microscopic as well as bulk properties will be presented, focusing on the modications introduced by the density dependent two-body force.

Theorie-Seminar

(Monash University)
3D Supernova Simulations -- Riddles, Successes and Surprises

Core-collapse supernovae are a challenging problem on the crossroads of astrophysics, nuclear and particle physics, and gravitational physics. They reveal themselves through a variety of observational signatures -- not only through the brilliant optical outburst, but also by their nucleosynthetic footprint, and by neutrinos and (though yet to be detected) by gravitational waves emitted from the supernova core. With the supernova engine hidden deep inside the stellar core from direct optical observations, our theoretical understanding of these events relies strongly on first-principle hydrodynamic simulation, which have recently become available in three dimensions (3D). As I shall demonstrate in this talk, these new simulations challenge many of our established views on the supernova explosion mechanism, but could also add an extremely interesting twist to nucleosynthesis processes in supernovae.

Theorie-Seminar

Raju Venugopalan (BNL)
TBA, note unusual time.

Theorie-Seminar

Baha Balantekin (University of Wisconsin-Madison)
Collective neutrino oscillations in a core-collapse supernova

In a core-collapse supernova nearly all the gravitational binding energy of the progenitor star is deposited in the proto-neutron star which cools
down by emitting about 10^{58} neutrinos. Hence near the neutron star, one can no longer ignore neutrino-neutrino interactions. The resulting
many-body system exhibits many interesting properties. In this I will
discuss the symmetries of this many-neutrino system, its collective
behavior as well as its duality to the BCS theory of superconductivity.

Theorie-Seminar

Caroline Robin (CEA)
Multiparticle-multihole configuration mixing description of many-body nuclear systems

Self-consistent methods and Configuration-Interaction techniques are among the most used and powerful approaches to the description of many-body nuclear systems. Based on different philosophies, they differ in their domain of applicability.

The Multiparticle-Multihole Configuration Mixing method takes advantages of both approaches in order to generalize the treatment of nuclear long-range correlations in a self-consistent manner. Although already widely used in other fields of physics such as atomic physics or quantum chemistry where the interaction is known, this method has only been recently proposed in the context of nuclear physics [1-3].

During my talk I will discuss first results concerning the spectroscopy of sd-shell nuclei. These first applications rely on the properties of the Gogny force and display encouraging results.

[1] N. Pillet, J.-F. Berger, and E. Caurier, Phys. Rev. C 78, 024305 (2008).
[2] N. Pillet, V. G. Zelevinsky, M. Dupuis, J.-F. Berger, and J. M. Daugas, Phys. Rev. C 85, 044315 (2012).
[3] J. Le Bloas, N. Pillet, M. Dupuis, J. M. Daugas, L. M. Robledo, C. Robin, and V. G. Zelevinsky, Phys. Rev. C 89, 011306 (2014).

Theorie-Seminar

Guy Moore (McGill University)
Transport and Hydrodynamics in Quantum Chromodynamics

Quantum Chromodynamics (QCD) is the theory underlying the strong interactions. Heavy ion collisions are probing QCD in a new hot many-body regime, whose interpretation requires a dialogue between experiment and theory. I will discuss our theoretical understanding of hot many-body QCD, focusing on transport phenomena and hydrodynamics. In particular, I will discuss the use and limits of perturbation theory.

Theorie-Seminar

Jiunn-Wei Chen (National Taiwan University)
When Mr. Berry Meets Mr. Wigner

Seeing the microscopic quantum physics in the macroscopic world is challenging, intriguing but possible! In efforts to uncover how the microscopic effect of quantum axial anomaly can show up in a macroscopic fluid, two seemingly very different approaches using the Wigner function and Berry phase were developed. We show in this talk that they are actually identical.

Theorie-Seminar

Carsten Urbach ()
Lattice QCD with 4 dynamical quark flavours: from the axial anomaly to two particle scattering

The field of lattice QCD has seen significant advances over the last few years. This concerns in particular the inclusion of dynamical quark degrees of freedom in the simulations. We will discuss recent results obtained from simulations with mass degenerate up and down quarks and physical strange and charm. We will focus on the physics of the eta and eta' meson system and the axial U(1) problem and pi-pi scattering.

Theorie-Seminar

Johanna Erdmenger (Max-Planck-Institut)

Theorie-Seminar

(Brookhaven National laboratory)

Theorie-Seminar

Huey-Wen Lin (University of Washington)
Lattice QCD for Nuclear Physics

Quantum chromodynamics (QCD) is the theory describing the strong interactions of gluon and quarks in the Standard Model. It is responsible for nuclei and their interactions, with applications from femtometer to astrophysical scales. Unfortunately, many interesting aspects of the low-energy physics of QCD, especially in nuclear phenomenology, are yet to be explored with controllable systematics. In order to get reliable quantitative results in the nonperturbative region of QCD, a direct approach composing by the quark and gluon degrees of freedom is desired.
Lattice gauge theory is just such a theoretical tool, making direct numerical calculations of QCD in a discretized spacetime. In this talk, I will give an introduction to lattice QCD and present the current status of the field as related to nuclear physics, giving examples of how lattice-QCD results provide crucial input to searches for new physics, and discuss the prospects for future developments.

Theorie-Seminar

Jens Braun (TU Darmstadt)
From Quarks and Gluons to Ultracold Fermi Gases and Back

The theory of the strong interaction describes the dynamics of the fundamental building blocks of nuclei, and the states of matter in the early stages of the universe. Relativistic heavy-ion collisions probe such
states, where we encounter temperatures much larger than in any other experiment on Earth. Far at the other end of the spectrum, experiments with fermionic atoms operate in the nano-Kelvin regime, providing a remarkably clean and versatile environment to test our understanding of a broad range of quantum phenomena: from condensation and superfluidity to the formation of bound states in strongly coupled systems.

In spite of the stark difference in the temperature scale, studies of ultracold atoms and the theory of the strong interaction are similar in many ways. In fact, it turns out that there are field-theoretical connections between these two fields. In addition, studies of ultracold gases provide insights into the nuclear many-body problem, also from a phenomenological point of view. However, a consistent first-principles description of the experimental data remains challenging in any case. In this presentation, I will give an overview of some of the most intriguing open questions in the phase diagram of the strong interaction. Finally, I will also discuss how recent technical developments, connecting ultracold Fermi gases and studies of the strong interaction, are providing us with a better understanding of collective phenomena underlying strongly coupled matter in general.

Theorie-Seminar

Zoltan Fodor (University of Wuppertal)
Lattice QCD: Approaching the continuum limit with physical quark masses

In this talk a short introduction to lattice QCD is presented and the importance of the physical limit (continuum extrapolation and physical quark masses) is emphasized. A few selected topics are discussed. The hadron spectrum and quark masses are determined. Techniques for many-nucleon sytems with sub-per-mil accuracies are presented. The transition temperature and the equation of state in the hot QCD plasma are calculated.

Theorie-Seminar

Witek Nazarewicz (University of Tennessee)
Atomic Nuclei: Many-Body Open Quantum Systems

The physics of Open Quantum Systems has attracted a lot of attention in many fields of physics. In atomic nuclei, the "openness" of the system manifests itself by the coupling to the many-body continuum representing various decay, scattering, and reaction channels. Due to the presence of particle thresholds, atomic nuclei form a network of correlated fermionic systems interconnected via reaction channels.
The space of states that are unbound to particle emission may have significant impact on spectroscopic properties of nuclei. Moving towards the drip lines, the coupling to the particle continuum becomes systematically more important, eventually playing a dominant role in determining structure. Theories of such nuclei need to take these additional ingredients and effects into account.
Many aspects of nuclei at the limits of the nuclear landscape, such as those related to the proximity of reaction channels, are generic and are currently explored in other open systems: molecules in strong external fields, quantum dots and wires and other solid-state microdevices, crystals in laser fields, and microwave cavities. Radioactive nuclear beam experimentation will answer crucial questions pertaining to all open quantum systems: What are their properties around the lowest energies where the reactions become energetically allowed (reaction thresholds)? What is the origin of states in which nuclei resemble groupings of nucleons into well-defined clusters, especially those of astrophysical importance? What should be the most important steps in developing the theory that will treat nuclear structure and reactions consistently? This presentation will address some of the research challenges pertaining to the interplay between nuclear openness, shell structure, and many-body correlations.

References:
[1] N. Michel, W. Nazarewicz, M. Ploszajczak and T. Vertse, J. Phys. G 36 (2008) 013101.
[2] J. Okolowicz, M. Ploszajczak, and I. Rotter, Phys. Rep. 374 (2003) 271
[3] J. Okolowicz, W. Nazarewicz, and M. Ploszajczak, Fortschr. Phys. 61, 66 (2013).

Theorie-Seminar

Aleksi Vuorinen (University of Helsinki)
Perturbative approaches to nonperturbative physics

I will discuss the role of perturbation theory in the description of strongly interacting matter either in or close to thermal equilibrium. Some examples of the quantities considered are the bulk thermodynamic and transport properties of hot quark-gluon plasma as well as the equation of state of cold and dense nuclear/quark matter. I will argue that a novel pairing of weak coupling techniques with other, nonperturbative approaches enables progress with problems that would otherwise be inaccessible by current first principles field theory tools.

Theorie-Seminar

Eric van Dalen (University of Tuebingen)
From nuclei to neutron stars with realistic NN interactions

In this seminar the results of theoretical investigations with realistic NN interactions are presented. The properties of infinite isospin asymmetric nuclear matter have been investigated in a relativistic Dirac-Brueckner-Hartree-Fock (DBHF) framework using the Bonn A potential. Results for the binding energy, the symmetry energy, the neutron-proton effective mass splitting, and the isovector nucleon optical potential are discussed. A problem is that the DBHF approach is too complex to be applied for other nuclear systems such as the neutron star crust and nuclei. However, these DBHF results can be applied to these systems within the framework of a density dependent relativistic mean field (DDRMF) theory. The predictions from this DDRMF model for the structure and properties of the neutron star crust and a few selected nuclei will be presented. Finally, an alternative to this DDRMF model, a low momentum interaction, will be discussed.

Theorie-Seminar

Johannes Kirscher ()
Universal aspects of the neutron-neutron and neutron-&#945; scattering systems through the telescope of an effective field theory

An effective field theory is a systematic description of a subset of the physical world of all observables. While those subsets may overlap, there is at least a trusted prescription of how to link their effective descriptions consistently. Although, effective field theories have been used in the realm of nuclei for decades, we still lack precise knowledge about the elements and boundaries of this peculiar subset, in particular, especially along the axis of increasing particle number.

I will present two analysis in this border area. First, the membership of three-body observables to the area of applicability of the effective field theory without pions is shown to yield a model-independent constraint on the notoriously hard-to-measure neutron-neutron scattering length [1].

Second, 4- and 5-body scattering systems are investigated, where we conjecture the existence of an additional scale for their leading-order description in pionless EFT. The cutoff dependence of S-matrix poles, i.e., resonances, in those systems is indicative to the conjecture of a correlation between 4- and 5-body data generalizing the 3- and 4-body Tjon-line analog [2].

[1] Johannes Kirscher and Daniel R. Phillips. Constraining the neutron-neutron scattering length using the effective field theory without explicit pions. Phys.Rev., C84:054004, 2011.
[2] Johannes Kirscher. in preparation. 2014.

Theorie-Seminar

Ragnar Stroberg (Michigan State University / NSCL)
Single-particle structure in silicon isotopes and the collapse of the N = 28 shell closure

A prominent theme in the study of the nuclear structure of exotic isotopes has been the disappearance of the shell closures found at stability and the appearance of new shell closures. The shell closure at N = 28 is of particular interest because it is the first shell closure that arises due to the strong spin-orbit splitting which is responsible all higher shell closures. N = 28 has been shown to disappear at large isospin, and this disappearance is particularly clear at 42Si (N = 28, Z = 14). This region is particularly difficult for shell model calculations with phenomenological interactions because they depend on cross-shell matrix elements which are poorly constrained by experimental data. Nonetheless, effective interactions have been developed which reproduce the collective observables around 42Si, while their microscopic predictions differ. In this talk, I will discuss the use of single-nucleon knockout reactions to investigate the disappearance of the N = 28 shell gap from a single-particle perspective.

Theorie-Seminar

Dr. Enrico Vigezzi and Prof. Francisco Barranco (INFN Milan / Univ. of Sevilla)
Core Polarization and Light Halo Nuclei: Structure and Reaction

The interplay of collective and quasi particle degrees of freedom plays an important role in the study of the nuclear structure and reactions.
We discuss its role in the physics of halo nuclei, where it leads to strong renormalization effects, producing the parity inversion observed in the ground state of N=7 isotones.
The exchange of collective vibrations between nucleon pairs leads to an induced interaction, which gives an essential contribution to the binding of two-neutron halos, and can be studied through the two-neutron transfer reaction 11Li(p,t)9Li, populating both the ground and the first excited state of 9Li.

Theorie-Seminar

Martin Hoferichter (University of Bern)
Spin-independent WIMP-nucleon scattering: scalar couplings and the pion-nucleon sigma-term

The interpretation of experiments aiming at the direct detection of Dark Matter by measuring the recoil on a nuclear target in high-sensitivity detectors requires knowledge of the scalar couplings of the nucleon.
We show how to avoid unnecessary and uncontrolled assumptions usually made in the literature about soft SU(3) flavor symmetry breaking in the determination of the up- and down-quark couplings, leaving the pion-nucleon sigma-term as the only free parameter. Moreover, we give an overview of the present status of our analysis of pion-nucleon scattering within the framework of Roy-Steiner equations, which aims at providing an updated extraction of the sigma-term from pion-nucleon phenomenology.

Theorie-Seminar

Jonathan Engel (University of North Carolina)
CP violation, EDMs, and Nuclear Structure'

Theorie-Seminar

Dr. Alessandro Lovato (ANL)
Electroweak response functions: from 12-Carbon to Neutron Matter

I will report on an ab initio calculation of the 12-Carbon charge form factor and sum rules of electromagnetic and neutral-current response functions. The longitudinal elastic form factor and the electromagnetic sum rules are found to be in satisfactory agreement with available experimental data. The transverse electromagnetic and neutral current sum rules receive large contributions from the two-body currents. In the Electromagnetic case they are needed for a better agreement with experimental data; this fact may have implications for the anomaly observed in recent neutrino quasi-elastic charge-changing scattering data off 12-Carbon.
The role played by nuclear correlations is discussed in both 12-Carbon and neutron matter case. In particular, I will show how the neutrino mean free path in cold neutron matter turns out to be strongly affected by both short and long range correlations, leading to a sizable increase with respect to the prediction of the Fermi gas model.

Theorie-Seminar

Gabriele Cescutti ()
Neutron capture elements in the Early Universe

In the last years our group has found many chemical anomalies observed
in very metal-poor halo stars suggest the first stellar generations to
have been fast rotators (spinstars). Recently, theoretical
computations have found that spinstars can also play a role in the
chemical enrichment of neutron capture elements providing a early
contribution of s-process. By means of a stochastic chemical evolution
model, it is possible to identify the spinstars s-process contribution
as the missing component responsible for the spread in the ratio
between light (Sr) to heavy (Ba) neutron capture elements. A specific
distribution is predicted for the isotopic ratio of Ba in halo stars
and this imprint could be the smoking gun of the role played by
spinstars in the spread of [Sr/Ba] ratio. Finally, regarding the
still unknown origin of the complementary r-process component, two
possible sites are tested - the electron capture supernovae and the
magneto rotational driven supenovae; only further investigations in
different Galactic component, as the bulge, will enable us to
constrain the real site.

Theorie-Seminar

Oleg Korobkin (Stockholm University)
The r-process in neutron star mergers: models and observational signatures

Theorie-Seminar

Barry Holstein (University of Massachusetts)
Hadronic Parity Violation

Theorie-Seminar

()
Three-dimensional simulation of magneto-rotationally driven core-collapse supernovae

The magneto-rotational mechanism represents an alternative explosion mechanism of core-collapse supernovae. The jet like explosion character associated with the magnetic mechanism may potentially explain the growing observational evidence that core-collapse supernovae are intrinsically aspherical. Moreover, it has been suggested that these events provide a promising site for the strong r-process.
We will present a detailed summary of the physical and mathematical model of our three- dimensional simulations of magneto-rotationally driven core-collapse. We evolved several different models varying the rotation law and the magnetic field configuration and studied the effect of these parameters on the dynamics. The discussion will be centered on the magnetic field amplification processes, angular momentum transport mechanisms and on the formation of the bipolar magnetohydrodynamical jets. We will also argue that magneto- rotationally driven supernovae present indeed a site for the strong r-process on the basis of thermodynamic histories of tracer particles in the simulations.

Theorie-Seminar

Dmitry Gridnev (FIAS)
Threshold Phenomena in Few-Body Systems: Halos and Efimov States

Nowadays in physics one finds numerous examples of few-body systems with large spatial extension. One could mention neutron halos in nuclear physics, Rydberg and Efimov states, negative ions in atomic and molecular physics. In all cases a large spatial extension of the many body wave function, which stretches beyond the classically allowed region, is a consequence of the fact that the energy of a bound state lies in close proximity to the dissociation threshold. A natural question arises, what would happen to a wave function of a system of N particles without clusters when a bound state approaches zero energy threshold. Relatively recently this question for three-body systems has been ultimately and rigorously resolved. It turns out that if none of the particle pairs have zero energy resonance then the system of three particles can possess a bound state at zero energy. Unlike negative energy bound states, which decay exponentially, a bound state with zero energy decays like an inverse power of a hyperradius, but still remains square integrable. The existence of a zero energy bound state sets limits on the size of two neutron halos, which are seen at the neutron drip line. If just one pair of particles has a zero energy resonance one gets a different situation: the ground state of three particles is no more square integrable at zero energy. This implies that a bound state, which approaches zero energy threshold totally spreads. Thereby, the wave function of three particles approaches a universal form, which does not depend on the details of the pair interaction. This is a first example of universality, which concerns wave functions rather than relations in the spectrum. Remarkably, the universal angular correlations match very well the dineutron peak that is seen in the wave functions of $^6$He and $^{11}$Li nuclei. If two or all three particle pairs have zero energy resonance, one arrives at the so-called Efimov effect. The obtained results, in particular, explain why the Efimov effect is only possible for three bosons, not more not less.

Theorie-Seminar

Michael Urban (IPN, Orsay)
BEC-BCS crossover in symmetric nuclear matter and neutron matter

The superfluid phase transition in nuclear and neutron matter is studied within a Nozieres-Schmitt-Rink like approach. In symmetric matter at low density, a Bose-Einstein condensate (BEC) of deuterons is formed, while in the limit of high density the BCS limit is recovered. However, the crossover between the two limits lies inside the unstable region of the liquid-gas phase transition. It turns out that the presence of correlated pairs in the gas somewhat reduces the unstable region. In neutron matter, because of the large negative neutron-neutron scattering length, the BCS side of the crossover can be studied almost from the unitary limit to the BCS limit. In this calculation, an effective low-momentum interaction (V_low-k) is employed. The main result is that at low density, the superfluid critical temperature is substantially reduced compared to the BCS one.

Theorie-Seminar

Carlo Barbieri (University of Surrey)
Many-body Propagator Theory with Three-Body Interactions: a Path to Exotic Open-Shell Isotopes

As ab-initio nuclear theory enter the mass range of A=40-100 particles, a great challenge is how to provide accurate predictions for the vast majority of open-shell (degenerate) isotopes. Here, the biggest challenges are to avoid the need for degenerate reference states and to include three-nucleon (and possibly many-nucleon) interactions that arise naturally in the nuclear Hamiltonian.
We have recently worked out and applied the Gorkov Green's function formalism up to second order in finite systems. Proof of principle calculations show that one can avoid multi-reference methods by breaking particle number symmetries and treating pairing explicitly in the reference states. We further worked out the principal terms in the diagrammatic expansion that contain three-body interactions, as well as the proper extension(s) of the Koltun sum rule.
These developments extend the applicability of ab-initio theory in the medium mass region from a few tens of closed-shells cases to a few hundreds of open-shell isotopes. Application with chiral nuclear interactions have allowed to establish a common mechanism by which three-nucleon interactions govern the dripline behaviour of nearby nitrogen, oxygen and fluorine isotopic chain. More application around the calcium chain have to come.
The talk will introduce the main features of the above formalism and quickly cover recent results for nuclear physics.

Theorie-Seminar

Arianna Carbone (University of Barcelona)
Nuclear and neutron matter with chiral forces in the self-consistent Green's function approach

Theorie-Seminar

(North Carolina State Univ.)
Supernovae, neutrinos, and nucleosynthesis

Theorie-Seminar

Sanjay Reddy (INT/University of Washington)
Forecasting neutron star temperatures

Theorie-Seminar

Takaharu Otsuka (University of Tokyo)
Shell and shape evolutions in exotic nuclei -how magic are 54Ca and 68-78Ni?

Theorie-Seminar

Dr. Susanne Kreim (CERN and MPIK Heidelberg)
From 3-body forces to neutron stars: the role of masses from ISOLTRAP

Experimentally, complementary observables are available to ameliorate our understanding of the nucleus, its mass being the most fundamental property. Together with the known mass of the individual constituents of the nucleus, the mass delivers the binding energy, which in turn reflects all underlying interactions of the nucleons. Precision measurements of masses can thus give insight into the faces of the nuclear force.
The investigation of structural effects towards the outskirts of the nuclear chart - like shell-quenching or the emergence of new magic numbers - are needed to unveil new aspects of the nuclear force. The calcium isotopic chain with a closed proton shell and two doubly-magic nuclei is an ideal test-bench for nuclear shell evolution. The masses of 53,54Ca determined by the multi-reflection time-of-flight mass spectrometer (MR-TOF MS) of the ISOLTRAP experiment establish a prominent shell closure at neutron number N = 32. The new masses illustrate the importance of microscopic calculations with three-nucleon forces derived from state-of-the-art chiral effective-field theory and increase our understanding of neutron-rich matter.

Masses of exotic nuclides also impose constraints on models for the nuclear interaction and thus affect the description of the equation of state of nuclear matter, which can be extended to describe neutron-star matter. With knowledge of the masses of nuclides near shell closures, one can also derive the neutron-star crustal composition. The mass of 82Zn determined by Penning-trap mass spectrometry allows constraining the neutron-star crust composition to deeper layers.

Theorie-Seminar

James P. Vary (Iowa State University)
Light-Front Hamiltonian approach to quantum field theory

Theorie-Seminar

Ian Cloet (Argonne National Laboratory)
Nucleon and Nuclear Structure in Continuum Strong QCD

Quantum Chromodynamics (QCD) is the only known example in nature of a fundamental quantum field theory that is innately non-perturbative. Solving QCD will have profound implications for our understanding of the natural world, for example, it will explain how light quarks and massless gluons bind together to form the observed mesons and baryons and hence the origin of more than 98% of the visible mass in the universe. Given QCDs complexity, the best promise for progress is a strong interplay between experiment and theory. I will discuss several theoretical studies in continuum QCD that have been motivated by key experimental results that challenged our understand of nucleon and nuclear structure. For example, the proton GE/GM form factor ratio, EMC effect and NuTeV anomaly. A perspective will be given on what these experiments tell us about the non-perturbative structure of QCD and several predictions will be presented that should be tested in future experiments.

Theorie-Seminar

Paul Springer ()
Finite Volume Effects and the Binder Cumulant in O(N)-Models

Theorie-Seminar

Reinhard Alkofer ()

Theorie-Seminar

Calvin W. Johnson (San Diego State University)
Beyond Noether's Theorem: What Happens when Symmetry Meets Randomness

You often hear about "fine-tuning" of parameters: some phenomena such as the abundances of heavy elements dependence sensitively on the exact strength of the interaction. What about the opposite? Are there phenomena which are exquisitely insensitive to the details of the interaction? Surprisingly, there are: to name just one of many, the ground state spins of even-even "nuclei" are dominated by J = 0 in shell-model simulations even when the interactions are completely random. The origin of this emergent behavior lies in surprising universality among many-body matrix elements, and can be found in a simple analytic model combining randomness and symmetry.

Theorie-Seminar

(Uni Basel)
The isotropic diffusion source approximation for supernova neutrino transport

Theorie-Seminar

Prof. Dr. Silas Beane (University of New Hampshire)
Nuclear physics from lattice QCD: a status report

I will discuss recent progress in calculating nuclear physics interactions and properties using lattice QCD. I will first focus on an area in which lattice QCD will soon be competitive with experiment; specifically, I will consider simple hypernuclear processes which are essential input into the nuclear equation of state relevant for a description of dense astrophysical objects. I will also discuss recent calculations of the spectrum of light nuclei and hypernuclei at the flavor SU(3) symmetric point. Finally, I will discuss very recent work which determines the nucleon-nucleon s-wave phase shifts at the SU(3) point.

Theorie-Seminar

Filippo Galeazzi (U. Valencia)
A step towards a more realistic description of binary neutron star mergers

Theorie-Seminar

Tilman Enss ()
Quantum limited spin transport in ultracold atomic gases

Can a real fluid flow without friction? Following the conjecture that quantum mechanics imposes a universal lower bound on the shear viscosity, this question is being studied intensively in several fields of physics ranging from quark-gluon plasmas to ultracold atomic gases. I will discuss the origin of this bound and present results for the frequency dependent shear viscosity of strongly interacting Fermi gases, which exhibits a universal high-frequency tail. Motivated by a recent experiment with spin-polarized clouds of atoms, I present recent calculations and discuss the prospect of a quantum bound for spin transport.

Theorie-Seminar

Heiko Hergert (The Ohio State University)
In-Medium Similarity Renormalization Group for Finite Nuclei

Theorie-Seminar

Janos Polonyi (Strasbourg)
Radiational and quantum time arrows

It is shown in the framework of a simple classical, harmonic model that irreversibility, generated by the environment is a spontaneous breakdown of the time reversal invariance which is driven by the environment initial conditions. The Closed Time Path method is outlined in classical mechanics as a systematic way to handle initial condition problems and dissipative forces by an action principle. The equivalence of the classical and quantum time arrows, generated by the environment is pointed out, as well.

Theorie-Seminar

Frederic Nowacki (Institut Pluridisciplinaire Hubert Curien, Strasbourg, France)
Correlations versus Shell Evolution Far From Stability

In this seminar, we will present some of the last developments in
microscopic nuclear structure calculations for exotic nuclei. In a
first part we will expose the basic ingredients of nuclear structure
calculations within the nuclear shell model framework. In a second
step we will discuss the development of collectivity in neutron-rich
nuclei around N=40, where experimental evidence suggest a rapid change
from the spherical to rotational regime, in analogy to the island of
inversion known at N=20. Theoretical calculations are performed
within the interacting shell model framework using an enlarged model
space outside 48Ca core comprising pf shell for the protons and f5/2,
p3/2,p1/2,g9/2,d5/2 orbits for neutrons. The effective interaction is
based on realistic two-body matrix elements which are corrected
empirically in its monopole part. We find a very good agreement
between theoretical results and available experimental data. We
predict different development of deformation in various isotopic
chains, with the maximum of collectivity occurring in the chromium
isotopes. The shell evolution responsible for the observed shapes will
be discussed in details, in parallel with the N=20 case. Finally the
stability of the r-process waiting point nucleus 78Ni and the
persistence of spin-orbit shell gaps will be discussed as the impact
of 3N forces in medium-mass nuclei.

Theorie-Seminar

(Brookhaven National Laboratory)
Understanding Quantum-Chromo-Dynamics with Heavy-Ion Collisions

Theorie-Seminar

Vladimir Skokov (Brookhaven National Laboratory)
Photon azimuthal anisotropy and magnetic field in heavy-ion collision

Theorie-Seminar

Andrea Idini ()
Medium polarization effects and pairing correlations in nuclei

Within the framework of nuclear field theory (NFT), the spectrum of atomic nuclei is described in terms of collective and quasiparticle degrees of freedom, that is, of elementary modes of nuclear excitation and of their interweaving. These modes are directly related to experiment. In fact, the associated transition densities and spectroscopic amplitudes are the basic ingredients entering in the calculations of inelastic, one- and two-particle transfer absolute differential cross sections. The workings of the Dyson equation, which propagates NFT medium polarization processes to all orders of perturbation, and which results in the dressing of quasiparticles and in the renormalization of the pairing interaction, will be discussed. The formalism will be applied to the superfluid nucleus 120Sn and to the exotic doubly closed shell nucleus 132Sn.

Theorie-Seminar

Micaela Oertel (LUTH, Observatoire de Paris, Meudon)
Phase transition towards strange matter

The phase diagram of a system constituted of neutrons and Lambda-hyperons in thermal equilibrium is evaluated in the mean-field approximation. It is shown that this simple system exhibits a complex phase diagram with first and second order phase transitions. Due to the generic presence of attractive and repulsive couplings, the existence of phase transitions involving strangeness appears independent of the specific interaction model. In addition I will discuss under which conditions a phase transition towards strange matter at high density exists, which is expected to persist even within a complete treatment including all the different strange and non- strange baryon states. I will show in particular that upon adding a charge degree of freedom, i.e. protons and electrons, the strangeness-driven phase transition stays almost unaffected contrary to the subsaturation liquid-gas transition. Consequences for stellar matter under the condition of strangeness equilibrium will be briefly discussed.

Theorie-Seminar

Aleksi Kurkela (McGill University)
How do quark-gluon plasmas thermalize?

Theorie-Seminar

Johannes Hofmann (Cambridge U)
Universal relations for fermions with short- and long-range interactions

The behaviour of cold Fermi gases is largely independent of the microscopic details of the interatomic interaction and can be described by a small set of parameters. It is, nevertheless, still a challenging task to calculate observables exactly, especially if the system is strongly interacting. However, if the observable depends on a large external scale, the functional dependence on that scale can be determined in closed analytical form. One method to derive such 'universal relations' is via the operator product expansion (OPE). I would like to introduce the application of this method to cold Fermi gases and to present results for the dynamic structure factor and the shear viscosity. I shall also give an overview of recent work that applies the OPE to fermions interacting with a long-range Coulomb interaction. I will conclude the talk by discussing a quantum anomaly in two-dimensional Fermi gases.

Theorie-Seminar

Dirk Rischke ()

Theorie-Seminar

Gert Aarts (Swansea University)
Exploring the strong interactions under extreme conditions

Theorie-Seminar

Harvey Meyer ()
Uses of Thermal Field Theory in a Moving Frame

Theorie-Seminar

Evgeny Epelbaum ()

Theorie-Seminar

Jan Pawlowski ()
From the quark-gluon plasma to the hadron gas: phase structure and thermodynamics of QCD

Theorie-Seminar

Aleksi Vuorinen ()
Bottom-up thermalization from AdS/CFT?

Theorie-Seminar

Michael Ilgenfritz (JINR, Dubna)
Influence of an external magnetic field on the thermal phase transition

I motivate the current interest in the cross-effects of QCD and Abelian Electrodynamics, in particular from the point of view of Heavy Ion Collisions. Since long the effect of an external magnetic field on chiral symmetry breaking (magnetic catalysis) has been considered in various models. More recently, the effect on the thermal phase transition of QCD and its deconfining and chiral symmetry restoration aspects is in the focus of effective models and of ab initio lattice simulations.
In the recent work of the Berlin group the circle of these investigations has been completed by a simulation of SU(2) lattice gauge theory with N_f flavors of dynamical, unrooted staggered quarks. For fixed mass (given in lattice units) the characteristic temperature of both intertwined crossovers rises with the magnetic field strength. For a couple of fixed beta-values, selected such to describe (i) the chirally broken phase, (ii) the crossover region or (iii) the chirally restored phase, we study the approach to the chiral limit for various values of the magnetic field. Within the chirally broken/confinement phase the chiral condensate is found to increase monotonically with a growing magnetic field strength. In the chiral limit the increase starts linear in agreement with a chiral model studied by Shushpanov and Smilga. Within the chirally restored/deconfinement phase the chiral condensate tends to zero in the chiral limit, irrespective of the strength of the magnetic field.

Theorie-Seminar

Evan O'Connor (CITA)
The Progenitor Dependence of the Preexplosion Neutrino Emission in Core-Collapse Supernovae

Theorie-Seminar

Reinhard Alkofer ()
Electron-Positron Pair Creation in Structured Pulses of Electric Fields

Electron-positron pair production for short laser pulses with multiple time-scale sub-structures is considered in the nonperturbative regime (Schwinger pair production). After a short discussion of the underlying mechanism the non-equilibrium quantum kinetic approach is introduced. Results for the momentum spectra of the created electron-positron pairs are presented. These may lead to new probes of light pulses at extremely short time scales. Considering suitably combined time-scales and field strengths can lead to a significant enhancement in the production rates (dynamically assisted Schwinger effect) and interferences in the obtained spectra. Recent attempts to apply optimal control theory for pulse shaping are reported. Last but not least, some results on pair creation in space- and time-dependent fields are presented.

Theorie-Seminar

Friedel Thielemann ()
Formation of the Heaviest Elements: Necessary Conditions, Astrophysical Sites, Nuclear Input

We give a short review on necessary conditions in order to achieve a sufficient neutron/seed ratio for an r-process to occur, what are the candidate astrophysical sites to fulfill such conditions (supernovae, magnetar-forming supernovae, quark (super-)novae, neutron star mergers,...), what is their role in the chemical evolution of galaxies, and did there existed a chance to produce superheavy elements in nature?

Theorie-Seminar

Raphael Hirschi (Keele University)
Impact of rotation on nucleosynthesis in massive stars

After a brief introduction to the evolution of massive stars, I will describe the effects of rotation and metallicity on their evolution. I will then present recent results on the impact of rotation on the weak s process at low metallicities. I will end the seminar with a discussion of key nuclear physics uncertainties relevant for massive star evolution and nucleosynthesis (neutron poisons, electron captures and C12-C12).

Theorie-Seminar

()
Towards First-Principle Models of Core-Collapse Supernovae

The collapse and the explosion of massive stars at the end of their
lives has been a foremost topic in computational astrophysics for
decades. After more than forty years, the mechanism responsible for
the explosion is still not fully understood, because the complex
interplay of multi-dimensional hydrodynamical effects (such as
convection and the so-called standing accretion shock instability),
neutrino transport, nuclear physics and general relativity has proved
extremely difficult to capture in numerical simulations. However, as I
shall demonstrate in this talk, the latest generation of
multi-dimensional core-collapse supernova models has considerably
advanced our understanding of the necessary ingredients for robust
explosions. Moreover, the successful explosion models now available
allow us to connect supernova theory more closely to nucleosynthesis
and chemogalactic evolution studies, as well as to the novel fields of
neutrino and gravitational wave astronomy.

Theorie-Seminar

Albino Perego (Basel)
Neutrino transport in multi-dimensional astrophysical simulations

Theorie-Seminar

Martin Savage (University of Washington)
Nuclear Forces from Quantum Chromodynamics

A century of coherent experimental and theoretical investigations have uncovered the laws of nature that underly nuclear physics. Quantum Chromodynamics (QCD) and Quantum Electrodynamics (QED), both quantum field theories with a small number of precisely constrained input parameters, dominate the dynamics of the quarks and gluons - the underlying building blocks of protons, neutrons, and nuclei. While the analytic techniques of quantum field theory have played a key role in understanding the dynamics of matter in high energy processes, they encounter difficulties when applied to low-energy nuclear structure and reactions, and dense systems.
Expected increases in computational resources into the Exa-scale during the next decade will provide the ability to numerically compute a range of important strong interaction processes directly from QCD with quantifiable uncertainties using the technique of Lattice QCD.
In this presentation, I will discuss the state-of-the-art Lattice QCD calculations of quantities of interest in nuclear physics,
progress that is expected in the near future, and the expected impact on nuclear physics.

Theorie-Seminar

Dean Lee (NC State University)
Effective field theory on the lattice: Ab initio calculations of nuclei and many-body systems

Effective field theory provides a systematic approach to interacting quantum systems at low energies and densities. Lattice effective field theory combines this approach with non- perturbative lattice methods. I discuss recent applications of lattice effective field theory to the physics of cold atomic superfluids, neutron matter, and nuclei. I also discuss new developments and ideas in the field.

Theorie-Seminar

Stephan Rosswog (Jacobs University Bremen)
The multi-messenger picture of compact object encounters

Theorie-Seminar

Witold Nazarewicz (University of Tennessee/ORNL)
Information content of a nuclear observable

Nuclei communicate with us through a great variety of observables. Some are easy to
measure, some take a considerable effort and experimental ingenuity. In this talk, we show how to assess the uniqueness and usefulness of an observable, i.e., its information content with respect to current theoretical models. We also quantify the meaning of a correlation between different observables and discuss how to estimate theoretical statistical uncertainties.
The methodology used in this work should be of interest to any theoretical framework that contains parameters adjusted to measured data.

Theorie-Seminar

Prof. Dr. Evgeny Epelbaum ()
Nuclear physics on the lattice

Chiral effective field theory provides a systematic framework toow-energy dynamics of few-nucleon systems and light nuclei based on (the symmetries of) QCD. Using a discretized version of this approach by treating pions and nucleons as point-like particles on an Euclidean space-time lattice allows to evaluate the path integral by Monte Carlo sampling and to access the properties of heavier systems. I describe the foundations of this method and consider the applications to the spectra of light nuclei.

Theorie-Seminar

Dr. Alexander E. Dorokhov (JINR, Dubna)
Pion form factors and decays

A short review of some recent experimental and theoretical studies of the light pseudoscalar mesons is presented. It concerns the problem of the muon g-2 and mesonic contributions to it, the rare mesonic decays to lepton pairs, the transition form factors at large momentum transfer, and a generalized quark transversity distribution of the pion.

Theorie-Seminar

Prof. Dr. Wolfram Weise ()
Nuclear Chiral Thermodynamics and Phases of QCD

Theorie-Seminar

Prof. Andreas Wipf ()
G2-Gauge Theory - A Laboratory for QCD

We review recent progress on the G2-Higgsmodel and G2-QCD with dynamical fermions. In contrast to real QCD this Gauge Theory has no sign problem and can be investigated at finite baryon density. We review results on the Phases of the Higgsmodel and discuss preliminary results for the model with dynamical fermions at finite temperature and finite density.

Theorie-Seminar

Prof. Dr. Michael Thies ()
Messages from exactly solvable fermionic field theories at finite temperature and density

Four-fermion theories in 1+1 dimensions of Gross-Neveu (discrete chiral symmetry) or Nambu--Jona-Lasinio (continuous chiral symmetry) type in the limit of a large number of flavors can be solved exactly. Nevertheless, they capture a rich variety of phenomena of interest to strong interaction physics. We review what has been learned about the phase diagrams of such models during the last decade. In the case of discrete chiral symmetry, the models can also be applied to conjugate polymers in condensed matter physics. In the case of continuous chiral symmetry, universal features emerge which are relevant for gauge theories as well, independently of whether fermions are confined or not.

Theorie-Seminar

Prof. Dr. Owe Philipsen ()
Effective theory for QCD at finite temperature and density from strong coupling expansions

Theorie-Seminar

Markus Huber (TU Darmstadt)
The puzzle of confinement: putting together some pieces

A characteristic feature of the strong interaction is the absence of free quarks and gluons from the particle spectrum. To explain this phenomenon, called confinement, many scenarios have been invoked. However, they are not mutually exclusive and it even turned out that some of them are intimately connected. I present results on two such scenarios: the dual superconductor picture of confinement and the Gribov-Zwanziger scenario. In the former chromomagnetic monopoles are supposed to confine quarks, whereas in the latter the so-called Gribov horizon plays an important role. Although these two pictures are based on quite different motivations, they are related to each other.

Theorie-Seminar

Jeff Greensite (San Francisco State University)
The Yang-Mills Vacuum Wavefunctional, and a Torelon Probe at High Temperature

Knowledge of the ground state wavefunctional of Yang-Mills theory ought to provide us with some insight into the infrared properties of the theory, confinement in particular. A number of proposals for this wavefunctional have been advanced in recent years, particularly in 2+1 dimensions. I will briefly review these proposals, and then describe the results of some recent numerical tests. I will also mention some new results which suggest that color electric flux tubes may survive at a range of temperatures above the deconfinement transition.

Theorie-Seminar

Prof. James Vary (Iowa State University)
Ab initio nuclear structure and reactions - perspectives and challenges

The vision of solving the nuclear many-body problem with fundamental interactions tied to QCD via Chiral perturbation theory appears to approach reality. The goals are to preserve the predictive power of the underlying theory, to test fundamental symmetries with the nucleus as laboratory and to develop new understandings of the full range of complex nuclear phenomena. Advances in theoretical frameworks (renormalization and many-body methods) as well as in computational resources (new algorithms and leadership-class parallel computers) signal a new generation of theory simulations that will yield valuable insights into origins of nuclear shell structure, collective phenomena and complex reaction dynamics. I will outline some recent achievements and present ambitious consensus plans along with their challenges for a coming decade of research that will strengthen the links between nuclear theory and nuclear experiment, between nuclear physics and astrophysics, and between nuclear physics and nuclear energy applications.

Theorie-Seminar

(TRIUMF, Canada)
Ab Initio Calculations of Light-Ion Reactions: Application to 7Be(p,gamma)8B Capture

Theorie-Seminar

Prof. Simon Hands (Swansea University, Wales)
Numerical Study of Dense Two Color Matter

After reviewing the QCD phase diagram and the problems in studying dense baryonic matter using orthodox lattice gauge theory methods, I present results of simulations of a QCD-like theory with gauge group SU(2) at non-zero quark chemical potential. Its behaviour as mu is increased is rich - there is evidence for three distinct regimes: first a Bose-Einstein condensate of tightly-bound but weakly-interacting diquarks; next a regime where the scaling of thermodynamic observables is consistent with a Fermi surface disrupted by a BCS instability;finally a deconfined phase. The deconfinement transition is distinct from the BEC/BCS crossover, hinting at quarkyonic behaviour.

Theorie-Seminar

PD Dr. Antonio Vairo ()
Non-relativistic bound states at zero and finite temperature: an effective field theory approach

Non-relativistic bound states are characterized by a hierarchy of energy scales that makes them well suited for an effective field theory treatment. I first illustrate this on the example of the hydrogen atom, for which I calculate the Lamb shift. Then I extend the formalism to the study of a quarkonium in a thermal bath. Quarkonium has been considered since long an ideal probe of the new state of matter, which is formed in high-energy heavy-ion experiments. The effect of the medium on the quarkonium spectrum and on its decay width is highlighted. The melting temperature of the bottomonium ground state is calculated.

Theorie-Seminar

Dr. Brian Tiburzi (Massachusetts Institute of Technology)
Going to Extremes: Strong Interactions in External Fields

At scales a few billion times smaller than microscopic, the properties of protons and neutrons arise from interactions between quarks and gluons. While these QCD degrees of freedom have been identified for well over a quarter century, quantitative predictions from QCD at low energies have remained elusive until quite recently. I will review difficulties inherent in treating strong interactions, and describe progress being made at predicting properties of QCD. The response of QCD to external fields, moreover, will be argued to provide a new window to the structure of protons and neutrons, and the study of QCD under extreme conditions.

Theorie-Seminar

Prof. Dr. Harvey Meyer ()
Extracting Real-Time Quantities from Euclidean Field Theory

In the context of Quantum Chromodynamics, non-perturbative observables such as the low-lying spectrum of hadrons can be extracted from the theory discretized on a Euclidean space-time lattice and simulated on a computer. Real-time quantities on the other hand, such as phase shifts, time-like form factors, or transport properties at finite temperature, cannot be straightforwardly computed. In some cases however real-time effects leave signatures in the Euclidean theory which can be isolated in certain kinematical regimes. I describe several examples of this type at zero and finite-temperature.

Theorie-Seminar

Prof. Dr. Jan Pawlowski ()
Strongly correlated systems: From dense and hot QCD to dilute cold quantum gases

Dense and hot QCD and dilute cold quantum gases both define extremes of matter in terms of density and temperature. While cold quantum gases are by now experimentally very well accessible, dense and hot QCD is probed indirectly by e.g. heavy ion collisions and astrophysical observations.

The understanding of both systems at arbitrary densities and temperatures requires non-perturbative methods that are universally applicable. In particular, they have to accommodate phase transitions, bound state formation and condensation phenomena (e.g. chiral symmetry breaking & hadronisation; molecule formation & Bose-Einstein condensation). Despite the enormous differences in temperature and density, the condensation phenomena in both systems show some commonalities. This is particularly interesting as it allows to benchmark theoretical advances due to the good experimental control of cold quantum gases.

In the present talk I first give an introduction to the physics of hot and dense QCD and cold quantum gases, as well as discussing the commonalities mentioned above. Then I report on current and planned activities in my group to understand and describe these strongly correlated systems and specifically to map-out the respective phase diagrams.

Theorie-Seminar

Prof. Dr. Thomas Papenbrock (University of Tennessee/Oak Ridge National Laboratory)
Strongly correlated quantum many-body systems: from atomic nuclei to cold atom gases

Atomic nuclei and trapped atom gases provide us with ample opportunities to study relevant and interesting correlations in finite quantum systems. This seminar reports on recent progress in the model-independent computation of atomic nuclei, with a focus on exotic nuclei and towards heavier masses. In addition, I will present a new effective theory for deformed rotational nuclei and present analytical solutions for the yrast states of mixtures of rotating Bose-Einstein condensates.

Theorie-Seminar

PD Dr. Lorenz von Smekal (TU Darmstadt)
Universal Aspects of Strongly Interacting Matter under Extreme Conditions

Strongly interacting matter fuels the stars and makes up almost the entire mass of the luminous universe. The underlying theory of quarks and gluons, Quantum Chromodynamics (QCD), completely specifies the interactions. However, these are so complex and non-linear that they have yet to be fully understood. Indeed, it is these strong interactions which under normal conditions confine quarks and gluons into the interior of hadrons. Understanding the generation of their masses, the confinement of quarks and gluons, the different phases of QCD at extreme temperatures or densities and the transitions between them are some of the great challenges in physics. In this talk I will discuss and illustrate universal aspects of chiral symmetry restoration and the deconfinement transition, and I will briefly describe where we are heading when investigating the QCD phase diagram with ab-inito non-perturbative QCD methods.

Theorie-Seminar

Dr. Paul Romatschke ()
Looking inside Neutron Stars: Microscopic Calculations Confront Observations

Compact stars offer a unique window of cold nuclear matter in the regime of extremely high densities. In particular, it has long been speculated that "exotic" phases of nuclear matter, such as quark matter could exist in the core of neutron stars. Lacking the tools to solve QCD accurately for densities expected in compact stars, simple toy models such as the MIT bag model for the QCD equation of state have been state of the art for the past 30 years. In this talk, I will argue that one can do better than that by using recent results from perturbative QCD. In fact, matching modern quark matter to realistic hadronic equations of state, one can reproduce available observations of neutron stars without any fine-tuning of parameters. I will discuss the implications on the cold nuclear matter equation of state and present and future compact star observations.

Theorie-Seminar

Prof. Dr. Lucas Platter ()
Effective Field Theories for Strongly-Interacting Systems

The description of strongly interacting few- and many-body systems is a constant challenge to theory. Effective field theories provide one path to the description of such systems provided a ratio of separated scales is available that can be exploited as an expansion parameter. I will discuss the application of EFTs to light nuclei and give overview over recent developments. I will furthermore address how this EFT can also be applied to halo nuclei and few- and many-body systems of ultracold atoms. If time permits I will also raise (and answer) the question how very heay nuclei can be described in a similar systematic fashion.

Theorie-Seminar

Dr. Joaquin Drut (Los Alamos National Laboratory)
Strongly interacting fermions: from electrons to quarks, and back

From electrons in graphene to quarks inside neutrons and protons, the realm of strongly-interacting quantum mechanics is filled with fascinating phenomena, unexpected connections and unresolved issues. Indeed, while much is known about fermions in general in weakly-interacting regimes, it is only with the advent of new experimental techniques and modern computational methods (analytic, numerical and mixed) that we are truly starting to understand even the simplest strongly-interacting systems.
In this talk, I will introduce the basic notions of this broad field (such as scales, symmetries and universality), and proceed to outline my research on strongly-interacting systems at the intersection of atomic and nuclear physics. I will also briefly describe my work on graphene using lattice field theory methods imported from quantum chromodynamics, and summarize some exciting new developments connecting the latest trends in quantum chemistry with a novel approach to nuclear structure.

Theorie-Seminar

Prof. Dr. Hans-Werner Hammer ()
Strongly interacting matter near unitarity: universality and beyond

I will discuss few-body systems near the unitary limit of infinite scattering length. Such systems can be described in an expansion around the ideal scale invariant limit. If three or more particles are present, the (approximate) scale invariance can be anomalous and log-periodic scaling behavior can be observed. I will show some applications in nuclear and particle physics as well as ultracold atoms.

Theorie-Seminar

Dr. Axel Maas ()
Strong Interactions in Extreme Conditions

The elementary constituents of nuclei are the quarks, which are 'glued' together by the gluons, the mediators of the strong nuclear force. Under extreme conditions, like in the very early universe or supposedly in the interior of neutron stars, this strong force changes its characteristics. To understand this is an ongoing theoretical endeavor. After a brief introduction to this project, a bottom-up approach to the quantum version of the strong interactions, QCD, will be presented. It will be discussed how quarks and gluons can be described both in the vacuum and in extreme conditions. Using this framework, information about the phase diagram of this theory will be deduced.

Theorie-Seminar

(CERN)
Thermodynamic and Transport Properties of Strongly Interacting Quantum Field Theories

Calculating bulk properties of Quantum field theories with large interaction strengths is a big challenge for theoretical physics. Examples are QCD matter in the early universe, in neutron stars or in heavy ion collisions but also condensed matter systems like ultra- cold quantum gases. In my talk I will describe an approach to these problems using modern renormalization group methods.

Theorie-Seminar

Dr. Kai Hebeler (Ohio State University)
New Frontiers in Nuclear Physics

Renewed interest in the physics of nuclei is stimulated by experiments at rare isotope facilities which open the way to new regions of exotic nuclei and by astrophysical observations and simulations of neutron stars and supernovae, which require controlled constraints on the equation of state of nucleonic matter. The interplay of chiral effective field theory, renormalization group methods and rapidly increasing computer power are enabling the development of new many-body methods to successfully attack these problems.

In this presentation I will give a general introduction to these new exciting develop- ments and discuss recent results on superfluidity in nuclei, the nuclear equation of state, and the structure of neutron stars. Finally, I will give an overview over various current projects which include the application of microscopic orbital-based density functional theory to nuclear systems, the investigation of large-momentum knock-out reactions in nuclei and the study of cooling processes in neutron stars.

Theorie-Seminar

Dr. Alexandros Gezerlis (University of Washington)
Bridging the Gap: Fermions in Nuclear Structure and Nuclear Astrophysics

In this talk I will discuss two general areas: a) the physics of heavy nuclei and its connection with the understanding of weak coupling in quantum many-body theory, and b) the physics of neutron-star crusts at intermediate to strong coupling.

More specifically, I intend to address two questions:
i) can Skyrme functionals have a self-consistent density dependence?
ii) can cold-atom experiments constrain nuclear theory?
These questions may appear to be unrelated, but I plan to show that they are intrinsically connected through, on the one hand, an abiding interest in experimental evidence and, on the other hand, a focus on many-body theory, whether in the form of microscopic Monte Carlo simulations on modern supercomputers, or more phenomenological approaches.

Theorie-Seminar

Dr. Jens Braun ()
Strongly-Interacting Fermions: From Hot and Dense QCD to Cold Many-Body Physics

The theory of the strong interaction, Quantum Chromodynamics (QCD), describes the generation of hadronic masses and the state of hadronic matter during the early stages of the evolution of the universe. While heavy-ion collision experiments provide us with information on hot and dense QCD, experiments with ultracold fermionic atoms provide a clean environment to test our understanding of the dynamical formation of condensates and the generation of bound states in strongly interacting systems.

Functional renormalization group techniques offer great potential for theoretical advances in both hot and dense QCD and cold many-body physics. Exploiting the connections between these different theories allows us to gain deeper insight into the physics of hadronization, condensation, and bound-state formation in strongly interacting theories. In the present talk, I review various aspects of such strongly- interacting systems and their connections, with an emphasis on finite-size effects and the structure of matter at extreme conditions.

Theorie-Seminar

Dr. Chihiro Sasaki (FIAS)
Problems and Challenges in Hadron Physics

I will present theoretical and phenomenological aspects of Quantum Chromodynamics, a gauge theory of the strong interaction of quarks and gluons composing hadrons. Selected issues are discussed with particular emphasis on the model buildings to be tested in heavy-ion collisions and/or nuclear astrophysics observations.

Theorie-Seminar

Pierre Capel ()
Nuclear reactions as a probe of nuclear structure far from stability

The study of nuclear structure far from stability has been enabled by the development of radioactive-ion beams. This technical breakthrough has led, among other things to the discovery of halo nuclei. These nuclei are light neutron-rich nuclei that exhibit a strongly clusterized structure: they can be viewed as a core that contains most of the nucleons, to which one or two neutrons are loosely-bound. Owing to their low separation energy, these neutrons tunnel far from the classically-allowed region and form a sort of a halo around the core.

Due to their short lifetime, they cannot be studied through usual spectroscopic techniques, and one must resort to indirect methods to infer information about their structure. Nuclear reactions are one of the best indirect methods to study nuclei far from stability.

During this seminar, I will present the dynamical eikonal approximation (DEA), which models reactions involving halo-nuclei at intermediate and high energies. To evaluate its validity, I will compare the DEA with other precise nuclear-reaction models: The time-dependent model, in which the projectile-target relative motion is described by a classical trajectory, and the continuum-discretised coupled channel model (CDCC), in which the continuum of the projectile is modelled by square-integrable functions. I will then present recent results obtained within the DEA in the study of halo nuclei and of reactions of astrophysical interest.

Theorie-Seminar

A. Rothkopf (Tokyo University)
Heavy Quark Potential from the Thermal Wilson Loop in Lattice QCD

Theorie-Seminar

K. Kashiwa ()
Nonlocal Polyakov-loop extended Nambu--Jona-Lasinio model and imaginary chemical potential

Theorie-Seminar

()
Nuclear Lattice Simulations

Theorie-Seminar

S. Borsanyi (Wuppertal)
QCD Thermodynamics from the Lattice

Theorie-Seminar

Dr. Hiro Fujii (Tokyo University)
Non-Abelian plasma instabilities in high-energy nuclear collisions

I will start with a general introduction to heavy ion physics and motivate the problem of pre-equilibrium time-evolution and gauge field instabilities, and then discuss the possible roles of the Nielsen-Olesen instabilities toward thermalization.