Theorie-Seminar

Organizers: Almudena Arcones, Jens Braun, Michael Buballa, Hans-Werner Hammer, Gabriel Martínez-Pinedo, Robert Roth, Achim Schwenk, Lorenz von Smekal, Jochen Wambach
Date: Thursdays, 14:00
Room: S2|11 10

Upcoming Seminars

11. 01. 2018 at 14:00
S2 11/10

Theorie-Seminar

Astrid Eichhorn (Heidelberg)
TBA

Past Seminars

09. 11. 2017 at 14:00
S2 11/10

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.

02. 11. 2017 at 14:00
S2 11/10

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.

11. 08. 2017 at 14:00
S2 11/10

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.

20. 07. 2017 at 14:00
S2 11/10

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.

12. 07. 2017 at 14:00
S2 11/207

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.

06. 07. 2017 at 14:00
S2 11/10

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.

29. 06. 2017 at 14:00
S2 11/10

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.

04. 05. 2017 at 14:00
S2 11/10

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.

16. 02. 2017 at 14:00
S2 11/10

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.

22. 12. 2016 at 14:00
S2 11/10

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.

15. 12. 2016 at 14:00
S2 11/10

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.

14. 12. 2016 at 13:30
S2 11/207

Theorie-Seminar

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

05. 12. 2016 at 15:30
S2 11/10

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)

01. 12. 2016 at 14:00
S2 11/10

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.

17. 11. 2016 at 14:00
S2 11/10

Theorie-Seminar

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

10. 11. 2016 at 14:00
S2 11/10

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.

20. 10. 2016 at 14:00
S2 11/10

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.

15. 09. 2016 at 14:00
S2 11/10

Theorie-Seminar

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

TBA

13. 09. 2016 at 14:00
S2 11/207

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.

08. 09. 2016 at 14:00
S2 11/10

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.

01. 09. 2016 at 14:00
S2 11/10

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.

04. 08. 2016 at 14:00
S2 11/10

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).

28. 07. 2016 at 14:00
S2 11/10

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)

19. 07. 2016 at 14:00
S2 11/207

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.

07. 07. 2016 at 14:00
S2 11/10

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.

30. 06. 2016 at 14:00
S2 11/10

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.

28. 06. 2016 at 15:00
S2 11/207

Theorie-Seminar

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

23. 06. 2016 at 14:00
S2 11/10

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.

09. 06. 2016 at 14:00
S2 11/10

Theorie-Seminar

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

02. 06. 2016 at 14:00
S2 11/207

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.

03. 05. 2016 at 14:00
S2 11/10

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.

22. 04. 2016 at 14:45
S2 11/10

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.

22. 04. 2016 at 14:00
S2 11/10

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.

21. 04. 2016 at 14:00
S2 11/10

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.

14. 04. 2016 at 14:00
S2 11/10

Theorie-Seminar

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

10. 03. 2016 at 14:00
S2 11/10

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.

18. 02. 2016 at 14:00
S2 11/10

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.

04. 02. 2016 at 14:00
S2 11/10

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.

02. 02. 2016 at 14:00
S2 11/207

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.

28. 01. 2016 at 14:00
S2 11/10

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.

10. 12. 2015 at 14:00
S2 11/10

Theorie-Seminar

Cristina Volpe (APC, Paris)
tba

08. 12. 2015 at 14:00
S2 11/207

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.

03. 12. 2015 at 14:00
S2 11/10

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.

26. 11. 2015 at 14:00
S2 11/10

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)

19. 11. 2015 at 14:00
S2 11/10

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.

29. 10. 2015 at 14:00
S2 11/10

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.

22. 10. 2015 at 14:00
S2 11/10

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.

15. 10. 2015 at 14:00
S2 11/10

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.

04. 08. 2015 at 14:00
S2 11/10

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.

30. 07. 2015 at 14:00
S2 11/10

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.

20. 07. 2015 at 11:00
S2 11/10

Theorie-Seminar

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

02. 07. 2015 at 14:00
S2 11/10

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.

24. 06. 2015 at 14:00
S2 11/10

Theorie-Seminar

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

28. 05. 2015 at 14:00
S2 11/10

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.

16. 04. 2015 at 14:00
S2 11/10

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).

08. 01. 2015 at 14:00
S2 11/10

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.

19. 12. 2014 at 11:30
S2 11/207

Theorie-Seminar

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

TBA

17. 12. 2014 at 11:00
S2 11/207

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.

16. 12. 2014 at 14:00
S2 11/10

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.

26. 11. 2014 at 14:00
S2 11/207

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.

11. 11. 2014 at 14:00
S2 11/10

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.

07. 11. 2014 at 16:00
S2 11/207

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.

03. 11. 2014 at 13:00
S2 11/207

Theorie-Seminar

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

30. 10. 2014 at 14:00
S2 11/10

Theorie-Seminar

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

23. 10. 2014 at 14:00
S2 11/10

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.

07. 10. 2014 at 14:00
S2 11/10

Theorie-Seminar

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

11. 09. 2014 at 14:00
S2 11/10

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).

10. 09. 2014 at 14:00
S2 11/10

Theorie-Seminar

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

14. 08. 2014 at 14:00
S2 11/10

Theorie-Seminar

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

17. 07. 2014 at 14:00
S2 11/10

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.

16. 07. 2014 at 15:15
S2 11/10

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.

10. 07. 2014 at 14:00
S2 11/10

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.

03. 07. 2014 at 14:00
S2 11/10

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 e ffects 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.

02. 07. 2014 at 14:00
S2 11/207

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.

01. 07. 2014 at 14:00
S2 11/10

Theorie-Seminar

Raju Venugopalan (BNL)
TBA, note unusual time.

16. 06. 2014 at 14:00
S2 11/10

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.

27. 05. 2014 at 14:00
S2 11/10

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).

20. 05. 2014 at 10:00
S2 14/024

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.

19. 05. 2014 at 09:00
S2 11/10

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.

06. 05. 2014 at 13:00
S2 11/10

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.

05. 05. 2014 at 13:00
S2 11/10

Theorie-Seminar

Johanna Erdmenger (Max-Planck-Institut)

05. 05. 2014 at 09:00
S2 11/10

Theorie-Seminar

(Brookhaven National laboratory)

02. 05. 2014 at 13:00
S2 11/10

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.

02. 05. 2014 at 09:00
S2 15/134

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.

28. 04. 2014 at 16:00
S2 11/10

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.

23. 04. 2014 at 14:00
S2 11/10

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).

16. 04. 2014 at 13:00
S2 11/10

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.

13. 03. 2014 at 14:00
S2 11/10

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.

11. 03. 2014 at 14:00
S2 11/10

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.

21. 02. 2014 at 14:00
S2 11/10

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.

20. 02. 2014 at 14:00
S2 11/10

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.

30. 01. 2014 at 14:00
S2 11/10

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.

23. 01. 2014 at 14:00
S2 11/10

Theorie-Seminar

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

10. 01. 2014 at 10:00
S2 11/10

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.

05. 12. 2013 at 14:00
S2 11/10

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.

14. 11. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

06. 11. 2013 at 14:00
S2 11/10

Theorie-Seminar

Barry Holstein (University of Massachusetts)
Hadronic Parity Violation

31. 10. 2013 at 14:00
S2 11/10

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.

24. 10. 2013 at 14:00
S2 11/10

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.

23. 10. 2013 at 11:00
S2 11/207

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.

17. 10. 2013 at 14:00
S2 11/10

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.

19. 09. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

18. 09. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

17. 09. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

31. 07. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

25. 07. 2013 at 14:00
S2 11/10

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.

18. 07. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

17. 07. 2013 at 14:00
S2 11/10

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.

16. 07. 2013 at 15:30
S2 11/10

Theorie-Seminar

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

15. 07. 2013 at 15:00
S2 11/10

Theorie-Seminar

Reinhard Alkofer ()

11. 07. 2013 at 14:00
S2 11/10

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.

20. 06. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

07. 05. 2013 at 14:00
S2 11/207

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.

18. 04. 2013 at 14:00
S2 11/10

Theorie-Seminar

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

07. 02. 2013 at 15:00
S2 11/207

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.

08. 01. 2013 at 13:00
S2 11/207

Theorie-Seminar

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

13. 12. 2012 at 14:00
S2 11/207

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.

19. 11. 2012 at 14:00
S2 11/10

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.

15. 11. 2012 at 12:00
S2 11/10

Theorie-Seminar

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

08. 11. 2012 at 14:00
S2 11/207

Theorie-Seminar

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

05. 11. 2012 at 14:00
S2 11/207

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.

01. 11. 2012 at 14:00
S2 11/207

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.

30. 10. 2012 at 16:00
S2 11/10

Theorie-Seminar

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

30. 10. 2012 at 12:00
S2 11/207

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.

26. 10. 2012 at 13:00
S2 11/10

Theorie-Seminar

Dirk Rischke ()

25. 10. 2012 at 13:00
S2 11/10

Theorie-Seminar

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

24. 10. 2012 at 16:00
S2 11/10

Theorie-Seminar

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

24. 10. 2012 at 13:00
S2 11/10

Theorie-Seminar

Evgeny Epelbaum ()

23. 10. 2012 at 16:00
S2 11/10

Theorie-Seminar

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

23. 10. 2012 at 13:00
S2 11/10

Theorie-Seminar

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

19. 10. 2012 at 14:30
S2 11/207

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.

17. 09. 2012 at 14:00
S2 11/207

Theorie-Seminar

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

02. 08. 2012 at 14:00
S2 11/207

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.

19. 07. 2012 at 14:00
S2 11/10

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?

05. 07. 2012 at 14:00
S2 11/10

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).

28. 06. 2012 at 14:00
S2 11/10

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.

14. 06. 2012 at 14:00
S2 11/207

Theorie-Seminar

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

13. 06. 2012 at 11:00
S2 11/10

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.

22. 05. 2012 at 12:00
S2 11/10

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.

21. 05. 2012 at 14:00
S2 11/10

Theorie-Seminar

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

18. 05. 2012 at 11:00
S2 11/10

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.

16. 02. 2012 at 14:00
S2 11/207

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.

09. 02. 2012 at 14:00
S2 11/207

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.

02. 02. 2012 at 14:00
S2 11/207

Theorie-Seminar

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

26. 01. 2012 at 14:00
S2 11/207

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.

12. 01. 2012 at 14:00
S2 11/207

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.

15. 12. 2011 at 14:00
S2 11/207

Theorie-Seminar

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

10. 11. 2011 at 14:00
S2 11/207

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.

28. 07. 2011 at 14:00
S2 11/207

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.

22. 07. 2011 at 11:00
S2 11/207

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.

29. 06. 2011 at 13:00
S2 11/207

Theorie-Seminar

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

26. 05. 2011 at 14:00
S2 11/207

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.

15. 04. 2011 at 15:00
S2 15/134

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.

15. 04. 2011 at 14:00
S2 15/134

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.

15. 04. 2011 at 13:00
S2 15/134

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.

15. 04. 2011 at 09:30
S2 15/134

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.

15. 04. 2011 at 08:30
S2 15/134

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.

14. 04. 2011 at 15:00
S2 15/134

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.

14. 04. 2011 at 14:00
S2 15/134

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.

14. 04. 2011 at 13:00
S2 15/134

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.

14. 04. 2011 at 09:30
S2 15/134

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.

14. 04. 2011 at 08:30
S2 15/134

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.

25. 03. 2011 at 11:15
S2 15/134

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.

25. 03. 2011 at 09:00
S2 15/134

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.

24. 03. 2011 at 11:15
S2 15/134

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.

24. 03. 2011 at 09:00
S2 15/134

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.

23. 03. 2011 at 14:00
S2 15/134

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.

18. 03. 2011 at 13:15
S2 15/134

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.

22. 02. 2011 at 10:30
S2 11/207

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.

18. 02. 2011 at 11:00
S2 11/207

Theorie-Seminar

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

10. 02. 2011 at 14:00
S2 11/207

Theorie-Seminar

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

20. 01. 2011 at 14:00
S2 11/207

Theorie-Seminar

()
Nuclear Lattice Simulations

13. 01. 2011 at 14:00
S2 11/207

Theorie-Seminar

S. Borsanyi (Wuppertal)
QCD Thermodynamics from the Lattice

27. 08. 2010 at 11:00
S2 11/207

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.

Address

Technische Universität Darmstadt

Institut für Kernphysik
Theoriezentrum

S2|11
Schlossgartenstraße 2
64289 Darmstadt

Secretary

Genette Kluckner

+49 6151 16 21551
+49 6151 16 21555

Stephanie Müller

+49 6151 16 21558
+49 6151 16 21555

Next Seminar

SFB Colloquium

on 14. 12. 2017 at 15:15
(S2 11/10)
Hans-Thomas Janka
TBA
zum Seitenanfang