Lunch Club Seminar

Quantum Field Theory of Strongly Interacting Matter

Organizers: Michael Buballa, Lorenz von Smekal
Date: Tuesdays, 12:00
Room: S2|11 10 or S2|11 207

Past Seminars

19. 07. 2016 at 12:00
S2 11/10

Lunch Club Seminar

Thorben Graf (SUBATECH, Nantes)
pQCD thermodynamics with massive quarks

Results for several thermodynamic quantities within the next-to-leading order calculation of the thermodynamic potential in perturbative QCD at finite temperature and chemical potential including non-vanishing quark masses are presented. These results are compared to lattice data and to higher-order optimized perturbative calculations to investigate the trend brought about by mass corrections. Furthermore, the findings of the investigation of the thermodynamics at nonzero isospin density for cold QCD are also presented.

26. 04. 2016 at 12:00
S2 11/10

Lunch Club Seminar

Stefano Carignano (INFN Gran Sasso )
Equation of state of imbalanced cold matter from chiral perturbation theory

We study the thermodynamic properties of matter at vanishing temperature for non-extreme values of the isospin chemical potential and of the strange quark chemical potential. From the leading order pressure obtained by maximizing the static chiral Lagrangian density we derive a simple expression for the equation of state in the pion condensed phase and in the kaon condensed phase. We find an analytical expression for the maximum of the ratio between the chiral perturbation energy density and the Stefan-Boltzmann energy density as well as for the isospin chemical potential at the peak in good agreement with lattice simulations of quantum chromodynamics. We speculate on the location of the crossover from the Bose-Einstein condensate state to the Bardeen-Cooper-Schrieffer state by a simple analysis of the thermodynamic properties of the system. For isospin chemical potetials greater or equal 2 m_pi the leading order chiral perturbation theory breaks down; as an example it underestimates the energy density of the system and leads to a wrong asymptotic behavior.

23. 06. 2015 at 12:00
S2 11/10

Lunch Club Seminar

Stefano Carignano (University of Texas at El Paso)
Crystalline chiral condensates as a component of compact stars

What are the properties of cold and dense quark matter? How is chiral symmetry restored at low temperatures and finite densities? While the next generation of heavy-ion experiments might help shed some light on this region of the QCD phase diagram, at the moment compact stellar objects provide the only known realization in nature of these extreme conditions. In this talk, I will show how the formation of inhomogeneous chiral symmetry breaking phases affects the equation of state of dense quark matter, and its consequences on the resulting mass-radius sequences for compact stars. I will also discuss the influence of a background magnetic field, which is shown to alter qualitatively the energy spectrum of inhomogeneous quark matter through the generation of an anomalous term. A similar situation occurs when dealing with a particular kind of inhomogeneous one-dimensional solution, namely a plane wave modulation called ``chiral spiral'' which arises naturally in QCD in the limit of of a large number of colors. If time allows, I will discuss the analogies between these two scenarios, and the difficulties arising when dealing with them in a 3+1-dimensional non-renormalizable model.

19. 12. 2014 at 13:30
S2 11/10

Lunch Club Seminar

Lukas Holicki (TU Darmstadt)
Simulations of LQC2D at Finite Temperature

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07. 11. 2014 at 12:00
S2 11/207

Lunch Club Seminar

Anton Cyrol (TU Darmstadt)
Gluonic Vertices of Landau Gauge Yang-Mills Theory in the Dyson-Schwinger Approach

We report on a self-consistent solution of the Landau gauge four-gluon vertex DSE. Our calculation includes all perturbatively leading one-loop diagrams, which constitutes the state-of-the-art truncation. As only input we use results for lower Green functions from previous Dyson-Schwinger studies that are in good agreement with lattice results. Within the truncation, no higher Green functions, which would have to be modelled, enter. Hence, the results depend only indirectly on models of Green functions. Our self-consistent solution resolves the full momentum dependence of the four-gluon vertex but is limited to the tree-level tensor structure. We calculate a few exemplary dressings of other tensor structures and find that they are suppressed compared to the tree-level structure except for the deep infrared where they diverge logarithmically. We employ the results to derive a running coupling. Furthermore, we study the coupled system of the three- and the four-gluon vertices to reduce the model dependence and to explore the convergence of the system of DSEs within the truncation scheme employed. For the scaling solution we establish a solution of the coupled system of vertices which provides promising evidence for the convergence.

28. 10. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Micaela Oertel (LUTH, CNRS/Observatoire de Paris, Meudon )
Building consistent neutron star models with magnetic field dependent equations of state

02. 09. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Mathias Wagner (Indiana University, Bloomington)
Insights into the QCD Phase Diagram from Conserved Charge Fluctuations

Fluctuations of conserved charges (baryon number, electric charge, strangeness, charm) have proven to be a valuable tool for the investigation of the QCD phase structure. They are available from Lattice QCD simulations and can also be measured experimentally at heavy-ion colliders like RHIC and LHC. I will provide an overview of the recent process on understanding QCD thermodynamics made by the BNL-Bielefeld-CCNU collaboration using fluctuation data.

Choosing appropriate ratios of the fluctuations and their correlations provide insights into various topic: Electric charge fluctuations allows us to provide a first-principles approach to determine the freeze-out temperature in heavy-ion collision. With strangeness and charm fluctuations we can address the question of deconfinement of strange and charmed degrees of freedom. Furthermore these data also provide evidence for the existence and thermodynamic importance of experimentally unidentified strange and charmed hadrons. These states also affect the values of the freeze-out temperature extracted using stochastical methods.

19. 08. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Axel Maas (Jena/Graz)
The Physics of Yang-Mills-Higgs Systems

Yang-Mills-Higgs theory offers a rich set of physics. In particular, in some region of its parameter space it has QCD-like behavior, while in some other range it is Higgs-like. Furthermore, for the choice of the gauge group SU(2) and an SU(2) Higgs flavor symmetry it is the Higgs sector of the standard model. Therefore, it is possible to study a plethora of phenomena within a single theory.

Here the standard-model version is studied using lattice gauge theory. It is investigated under which circumstances a perturbative treatment can be successful in describing the physical excitations. In general, it is found that W-to-Higgs mass ratio is decisive for the type of physics. Furthermore, the region relevant for a 125 GeV Higgs will be investigated, analyzing whether additional observable states could arise from non-perturbative physics.

24. 06. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Achim Heinz (Frankfurt)
Inhomogeneous phases in 1+1 and 1+3 dimensional effective models

The requirement of the chiral condensate to be constant over space is too restrictive. In this talk we present two recent studies on the subjects.

1) We investigate the formation of the chiral density-wave (CDW) in the framework of the so-called extended linear sigma model (eLSM), which is an effective model of QCD with (pseudo)scalar and (axial-)vector mesons as well as the nucleon and its chiral partner in the mirror assignment. As a result we find that an inhomogeneous phase in the form of a CDW dominates the high density regime.

2) We introduce the finite mode approach, which is a lattice-inspired numerical method to study inhomogeneous condensation in a general framework. After reproducing well-known analytic results for $1+1$ dimensional models, we turn to the $3+1$ dimensional NJL model: the famous inhomogeneous island as well as the inhomogeneous continent are investigated. We show that the continent remains finite and persists for different constituent quark masses and different number of regulators.

17. 06. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Christoph Kommer (Heidelberg)
How to use field theoretical methods in the context of cosmological nonlinear structure formation

The understanding of analytical methods in nonlinear structure formation in cosmology is highly important when considering alternatives to numerical simulations in order to obtain reliable results on sufficiently small scales or even to eventually explain scalings like the NFW profile from simulations fundamentally. Without referring to standard perturbation theory techniques in the first place one obtains fully resummed evolution equations for n-point propagators out of equilibrium. Using preliminiaries from statistical field theory a generating functional is constructed from which the desired correlators are obtained by functional differentiation assuming a Vlasov-Poisson system. Via functional methods such as the renormalization group, Schwinger-Keldysh contours or a 2PI effective action functional one in the end obtains a formally closed set of equations at second order in the correlators using a cubic action in the case of gravitational instabilities.

03. 06. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Federico Marquez (Santiago de Chile)
Thermodynamic instabilities in nonlocal Nambu-Jona-Lasinio models

04. 04. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Anton Cyrol (TU Darmstadt)
The Landau gauge four-gluon vertex in the Dyson-Schwinger approach

We report on the first Dyson-Schwinger calculation of the four-gluon vertex dressing function that contains all perturbatively leading one-loop diagrams. To diminish the impact of non-Bose-symmetric and hence unphysical parts, we symmetrize the four-gluon vertex Dyson-Schwinger equation (DSE). The propagators are dressed by the numerical results from Ref. [1] that agree well with lattice data. We take the ghost-gluon vertex as bare and dress the three-gluon vertex by the results obtained in Ref. [2]. By iterating the four-gluon vertex DSE, we find that the swordfish diagram is the dominant one. We compare our results to models used in previous Dyson-Schwinger calculations and determine the running coupling from the four-gluon vertex. Finally, an outlook for my master's thesis is given.
References:
[1] M. Q. Huber and L. von Smekal, JHEP 1304, 149 (2013), arXiv:1211.6092.
[2] A. Blum, M. Q. Huber, M. Mitter, and L. von Smekal, (2014), arXiv:1401.0713.

04. 02. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Georg Bergner ()
Supersymmetry on the lattice and simulations of supersymmetric Yang-Mills theory

21. 01. 2014 at 12:00
S2 11/10

Lunch Club Seminar

Sam Jones (Keele University)
Evolution of electron capture supernova progenitors

New models, improved nuclear physics and hydrodynamic mixing uncertainties.

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

Lunch Club Seminar

Philipp R. John (Dipartimento di Fisica e Astronomia, Universita di degli Studi Padova e Instituto Nazionale di Fisica Nuclear, Sezione di Padova, I-35131 Padova, Italy)
Study of shape transitions in Osmium isotopes with AGATA at LN-Legnaro

03. 12. 2013 at 12:00
S2 11/10

Lunch Club Seminar

Anja Habersetzer (Frankfurt)
Tau Decay and Spectral Functions

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

Lunch Club Seminar

Noriyoshi Ishii (CCS, Tsukuba University)
LS force and anti-symmetric LS force from lattice QCD

We will present our recent results on LS force(NN) and anti-symmetric LS force (hyperon interaction) from lattice QCD. We begin with a brief review of our strategy in constructing inter-baryon potentials and some related topics. The potentials are obtained from Nambu-Bethe-Salpeter (NBS) wave functions [HAL QCD method], which has been applied to many systems, such as NN, YN, YY, NNN, etc. These studies are restricted to local potentials (potentials which do not involve derivatives) in the parity-even sector. The restriction is due to source functions which these calculations employ, i.e., these calculations employ source functions with A1 representation of the cubic group such as the wall source and a smearing source. By using a momentum wall source with non-trivial cubic group transformation property, we study NN potentials in the parity-odd sector as well as the LS potentials. (LS potentials involve a single derivative) A strong attractive LS force with a weak repulsive central force in spin triplet P-wave channels lead to an attraction in the 3P2 channel, which is related to the P-wave neutron pairing in neutron stars. We extend this method to the hyperon sector, and consider a phenomenologically expected cancellation between the symmetric and the anti-symmetric LS potentials in the flavor SU(3) symmetric limit.

22. 10. 2013 at 12:00
S2 11/10

Lunch Club Seminar

Kirill Boguslavski ()
Universality and turbulence in expanding systems

We study the non-equilibrium dynamics of longitudinally expanding systems using classical-statistical real-time lattice simulations. For non-abelian plasmas, different thermalization scenarios have been proposed to occur in ultrarelativistic heavy-ion collisions in the limit of weak couplings and large nuclei. Remarkably, we observe a turbulent attractor solution that distinguishes between these different scenarios.
Extending our study to other longitudinally expanding quantum systems, we also observe a turbulent attractor solution in the scalar field theory. At early times, one finds an inverse particle cascade as for the non-expanding case, leading to Bose-Einstein condensation. At later times, in the semihard momentum region of the scalar system, the extracted universal properties of the scalar and non-abelian gauge theory agree to very good accuracy. Moreover, our data analysis suggests that elastic processes govern the dynamics at harder momenta.

15. 10. 2013 at 12:00
S2 11/10

Lunch Club Seminar

Bardiya Bahrampour (TU Darmstadt)
Topological Field Theory Methods for Gauge-Fixing on the Lattice

11. 06. 2013 at 12:00
S2 11/207

Lunch Club Seminar

Sixue Qin ()
Extraction of Observables from Meson Correlation Functions

14. 05. 2013 at 12:00
S2 11/207

Lunch Club Seminar

Kirill Boguslavski ()
Turbulent thermalization in heavy-ion collisions

Non-equilibrium fixed points and wave turbulence have been predicted for systems across different energy scales ranging from early-universe inflaton dynamics to experiments with ultracold atoms. Using classical-statistical lattice gauge theory simulations, the existence of a non-thermal fixed point is demonstrated for the space-time evolution of heavy-ion collisions in the limit of large nuclei at high energy. Most remarkably, the obtained scaling exponents can be explained by ordinary elastic scattering. We extend our discussion to the O(N) scalar field theory in a longitudinally expanding background to compare the scaling exponents and thus the underlying processes.

12. 03. 2013 at 12:30
S2 11/10

Lunch Club Seminar

Andreas Windisch (KFU Graz)
Calculating the analytic structure of QFT Greens functions on GPUs

We use Graphics Processing Units (GPUs) to calculate the analytic structure of QFT Green's functions. We extend a technique developed for the evaluation of the analytic structure of scalar glueball operators at the Born level such that it is suitable for a fully non-perturbative treatment in the Dyson-Schwinger approach. In particular we discuss how this method can be used to obtain the analytic structure of the Landau gauge quark propagator.

12. 03. 2013 at 12:00
S2 11/10

Lunch Club Seminar

Markus Hopfer (KFU Graz)
The Quark-Gluon Vertex in Landau gauge QCD

The coupled system of the quark-gluon vertex and quark propagator Dyson-Schwinger equations (DSEs) is investigated within Landau gauge QCD. The aim is to get a deeper insight into the mechanisms of quark confinement and dynamical chiral symmetry breaking and into a possible relation between these two phenomena. To this end an earlier study is extended by improving systematically on the truncations imposed on the quark-gluon vertex DSE. A clear infrared enhancement for all tensor structures of the quark-gluon vertex is obtained.

19. 02. 2013 at 12:00
S2 11/10

Lunch Club Seminar

Bardiya Bahrampour (TU Darmstadt)
Gauge-fixing for SU(N) on the lattice without 0/0 problem

Master thesis proposal presentation.

22. 01. 2013 at 12:00
S2 11/207

Lunch Club Seminar

Meng-Ru Wu (TU Darmstadt)
Neutrino oscillations in supernovae

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

Lunch Club Seminar

Alexander Stoffers (Stony Brook)
Holographic Pomeron

We briefly review the approach to dipole-dipole scattering
in holographic QCD. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in
both a conformal and confining background, identifying the holographic
direction with the virtuality of the dipoles. The wee-dipole
density is related to the string tachyon diffusion in both virtuality
and the transverse directions. We give an explicit derivation of the
dipole saturation momentum both in the conformal and confining metric.
Our holographic result for the dipole-dipole cross section and the it
wee-dipole density in the conformal limit are shown to be identical in
form to the BFKL pomeron result when the non-critical string
transverse dimension is D_perp=3. The total dipole-dipole cross section is
compared to DIS data from HERA. We further compare the holographic
result for the differential cross section to proton-proton and deeply
virtual Compton scattering data.

27. 11. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Issaku Kanamori ()
Supersymmetry on the lattice with Q-exact formulations

Although supersymmetry is broken with lattice regularization, a BRST-like part of the supersymmetry can be exactly realized on lattice in some systems. In low dimensional cases, this symmetry (Q-symmetry) is strong enough to guarantee the restoration of full supersymmetry in the continuum limit. I will present some results from 2-dimensional super Yang-Mills from lattice simulations with such symmetry. Another advantage of exact Q-symmetry is that it allows to define the Witten index at the lattice level, which is a useful index to discuss spontaneous supersymmetry breaking. I will also present how to measure the Witten index from lattice simulations.

20. 11. 2012 at 12:00
S2 11/207

Lunch Club Seminar

(Uni Basel)
White dwarf collisions as a Type Ia Supernova channel: a smoothed particle hydrodynamics approach

06. 11. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Michael Urban (IPN, Orsay)
Pygmy resonance and torus mode within Vlasov dynamics

The pygmy dipole resonance in neutron-rich nuclei is studied within the framework of the Vlasov equation which is solved numerically. The interaction used in the Thomas-Fermi ground state and in the Vlasov equation is derived from an energy functional which correctly describes the equation of state of nuclear matter and neutron matter. It is found that the pygmy resonance appears in the electric dipole response of all nuclei with strong neutron excess, the energies and transition probabilities being in reasonable agreement with experimental results. Since the Vlasov equation does not account for any shell effects, this indicates that the existence of the pygmy resonance is a generic phenomenon and does not rely on the specific shell structure. Besides the electric dipole response, the isoscalar toroidal response is calculated. The transition densities and velocity fields are discussed. A comparison of the peak positions and velocity fields suggests that the pygmy resonance can be identified with one of the low-lying modes excited by the isoscalar toroidal operator.

16. 10. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Soeren Schlichting ()
Aspects of the non-equilibrium dynamics of heavy ion collisions

07. 08. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Frank Saueressig ()
Renormalization group and quantum gravity, Lecture 3

31. 07. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Jan Stockemer ()
Real-Time Functional Renormalization Group

19. 06. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Frank Saueressig ()
Renormalization group and quantum gravity, Lecture 2

12. 06. 2012 at 12:00
S2 11/10

Lunch Club Seminar

Marcella Ugliano (Max Planck Institute for Astrophysics)
Explosion and remnant systematics for neutrino-driven supernovae

05. 06. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Frank Saueressig ()
Renormalization group and quantum gravity, Lecture 1

15. 05. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Matthias Hempel (University of Basel)
New equations of state in core-collapse supernova simulations

We present new equations of state (EOS) which are available for use in astrophysical simulations. Their characteristic properties are confronted with experimental and observational constraints, with focus on recent results for the symmetry energy. The role of the EOS in core-collapse supernovae is investigated by use of spherical simulations with detailed neutrino transport. First we briefly discuss the distributions of heavy nuclei during collapse and the abundant appearance of light nuclei like deuterons and tritons in the shock heated matter. Then we analyze the role of the high-density EOS in the later post-bounce phase. In addition to the properties of the cold nuclear matter EOS, we find that complementary temperature effects can be crucial for the dynamics.

24. 04. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Sandeep Chatterjee (Indian Institute of Science, Bangalore, India )
Model Investigation of QCD thermodynamics and phase diagram

We consider the (2 + 1) flavor Polyakov Quark Meson Model (PQM) and study the effect of including fermion vacuum fluctuations on the thermodynamics and phase diagram. The variation of the thermodynamic quantities across the phase transition region becomes smoother. This results
in better agreement with the lattice QCD (LQCD) data. The critical end point is pushed into higher values of the chemical potential. We then go on to study the fluctuations (correlations) of conserved charges in PQM up to sixth (fourth) order. Comparison is made with LQCD wherever available and overall good qualitative agreement is found, more so for the case of the normalised susceptibilities. Our study provides a solid basis for the use of PQM as an effective model to understand the topology of the QCD phase diagram.

17. 04. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Leonard Fister ()
Yang-Mills Theory at Non-Vanishing Temperature

We study the temperature dependence of correlators in Yang-Mills theory. For this purpose we utilise a purely thermal renormalisation group flow equation, and obtain the full thermal propagators. Interestingly, the electric screening mass is sensitive to the confinement-deconfinement phase transition. We also compute thermodynamic quantities such as the pressure.

28. 02. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Kirill Boguslavski (TU Darmstadt)
Field Theory Description of Graphene - Part II

14. 02. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Shun Furusawa (Waseda University, Japan)
Sub-nuclear density equations of state and compositions of nuclear matter for core-collapse supernovae

We calculate a new equation of state for baryons at sub-nuclear densities for the use in core-collapse simulations of massive stars. The formulation is the nuclear statistical equilibrium description and the liquid drop approximation of nuclei. The model free energy to minimize is calculated by relativistic mean field theory for nucleons and the mass formula for nuclei with atomic number up to ~1000. We have also taken into account the pasta phase. We find that the free energy and other thermodynamical quantities are not very different from those given in the standard EOSs that adopt the single nucleus approximation. On the other hand, the average mass is systematically different, which may have an important ramification to the rates of electron captures and coherent neutrino scatterings on nuclei in supernova cores.

07. 02. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Naoki Yamamoto (INT Seattle)
The QCD phase diagram: universality and continuity

We discuss the phase diagrams of QCD and QCD-like theories from the viewpoints of the large-Nc universality and the quark-hadron continuity. First we show that the whole or the part of the phase diagrams are universal between QCD and QCD-like theories in the limit of large number of colors N_c. From our universality and QCD inequalities, we derive some rigorous results on the chiral phase transition at high temperature. Second we argue that the continuity from hadronic matter to quark matter should universally appear in flavor-symmetric QCD and QCD-like theories at low temperature and high density. We also discuss possible implications of our results.

31. 01. 2012 at 12:00
S2 11/207

Lunch Club Seminar

Kirill Boguslavski (TU Darmstadt)
Field Theory Description of Graphene

06. 12. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Alexander Semke (TU Darmstadt/GSI)
On the quark-mass dependence of the baryon ground-state masses

We perform a chiral extrapolation of the baryon octet and decuplet masses in a relativistic formulation of chiral perturbation theory. A partial summation is assumed as implied by the use of physical baryon and meson masses in the one-loop diagrams. Upon a chiral expansion our results are consistent with strict chiral perturbation theory at the next-to-next-to-next-to-leading order. All counter terms are correlated by a large-Nc operator analysis. Our results are confronted with recent results of unquenched three flavor lattice simulations. We adjust the parameter set to the pion-mass dependence of the nucleon and omega masses as computed by the BMW group and predict the pion-mass dependence of the remaining baryon octet and decuplet states. The current lattice simulations can be described accurately and smoothly up to pion masses of about 600 MeV. In particular we recover the recent results of HSC without any further adjustments.

29. 11. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Christian Schmidt ()
Recent Lattice Results on the QCD Transition and Conserved Charge Fluctuations

We presents results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed using the p4, asqtad and HISQ/tree actions with 2 + 1 favors on lattices with temporal extent N = 6, 8 and 12 to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit.

The chiral transition temperature (Tc) is analyzed in terms of scaling functions, associated with the critical point in the massless limit of the two light quarks. Our main result is Tc=154(9) MeV, which is consistent with our estimate of Tc from the analysis of the peak positions of the chiral susceptibility. This method can also be extended to a small but nonzero chemical potential.

Furthermore, we discuss fluctuations of baryon number, electrical charge and strangeness and compare them to the hadron resonance gas, as well as to experimental results from heavy ion collisions. We generally find good agreement with HRG model results for temperatures T < 150 MeV
but observe significant deviations in the temperature range 160 MeV < T < 170 MeV which show qualitative differences for the three conserved charge sectors. These findings are expected to be of
relevance for the discussion of freeze-out conditions in relativistic heavy ion collisions.

01. 11. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Hans-Peter Pavel (TU Darmstadt and JINR Dubna)
Gauge invariant coarse graining approach to QCD at strong coupling

For the complete description of the physical properties of QCD, such as color confinement, chiral symmetry breaking, the spectra and strong interactions of hadrons, and the formation of condensates and flux-tubes, it might be advantageous to first reformulate QCD in terms of gauge invariant dynamical variables, before applying any approximation schemes. Using a canonical transformation of the dynamical quark and gluon variables, which Abelianises the non-Abelian Gauss-law constraints, such a reformulation can be achieved for 2-color QCD and is expected to be generalisable to the case of real QCD. The resulting unconstrained QCD-Hamiltonian admits a systematic expansion in the number of spatial derivatives. Introducing an infinite lattice with box length a and coarse graining the local gauge invariant fields, a systematic strong coupling expansion of the Hamiltonian in lambda= g^(-2/3) can be obtained, with the free part being the sum of Hamiltonians of Dirac-Yang-Mills quantum mechanics of constant fields for each box, and interaction terms of higher and higher number of spatial derivatives connecting different boxes. The corresponding deviation from the free glueball/hadron spectrum, obtained earlier for the case of Dirac-Yang-Mills quantum mechanics of spatially constant fields, is calculated using perturbation theory in lambda. As a first step, the interacting glueball vacuum and the energy spectrum of the interacting spin-0 glueball are obtained to order lambda^2. Its relation to the renormalisation of the coupling constant in the IR is discussed, indicating the absence of infrared fixed points.

25. 10. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Micaela Oertel (CNRS/Observatoire de Paris)
Collective excitations in the neutron star inner crust

It has been known for a long time that within the different structures inside a neutron star we can find superfluid and superconducting ones. The first observational indications were the glitches, and more recently observations of the surface thermal emission have been discussed in this context. The latter
is an observable, which depends on heat transport properties and is thus very sensitive to the superfluid and superconducting character of the different structures inside the star. Here, I will present a study of the spectrum of collective excitations in the inhomogeneous phases in the neutron star inner crust within a superfluid hydrodynamics approach. The aim is to describe the whole range of wavelengths, from the long-wavelength limit which can be described by macroscopic approaches and which is crucial for the low-energy part of the spectrum, to wavelengths of the order of the dimensions of the Wigner-Seitz cells, corresponding to the modes usually described in microscopic calculations. As an application, I will discuss the contribution of these collective modes to the specific heat in comparison with other known contributions.

04. 10. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Michael Ilgenfritz (JINR, Dubna)
Streamlines in SU(2) gluodynamics and semi-classical confinement

The infrared structure of SU(2) Yang-Mills theory is studied by means of lattice gauge simulations using a new constrained cooling technique. This method reduces the action while all Polyakov lines on the lattice remain unchanged. In contrast to unconstrained cooling, quark confinement is still intact. A study of the Hessian of the Yang-Mills action shows that low action (semi-) classical configurations can be achieved, with a characteristic splitting between collective modes and higher momentum modes. Besides confinement, the semiclassical configurations also support the topological susceptibility and generate spontaneous breakdown of chiral symmetry. We show that they possess a cluster structure of locally mainly (anti-)selfdual objects. By contrast to an instanton or a meron medium, the topological charge of individual clusters is smoothly distributed.

27. 09. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Kai Schwenzer (Washington University, St Louis)
Bridging the gap by shaking superfluid matter

In cold compact stars matter is expected to be superfluid and transport processes are significantly suppressed. Yet, we show that weak reactions become strongly enhanced and approach their ungapped level when the star undergoes density oscillations of sufficiently large amplitude. We present results for the neutrino emissivity and the bulk viscosity due to weak Urca processes in hadronic, hyperonic and quark matter and discuss different superfluid and superconducting pairing patterns.

26. 07. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Lukas Janssen ()
Quantum phase transitions in 3d relativistic fermion systems

3d relativistic fermion system have fascinating applications to condensed-matter systems: In particular, QED3 and the 3d Thirring model are actively discussed, e.g., as effective theories describing different regions of the cuprate phase diagram and the electronic properties of graphene. Nonetheless, these theories are likewise intrinsically interesting: most notably, it is expected that chiral symmetry breaking is prohibited once the number of fermion flavors is larger than a critical value. In this talk I review the 3d Thirring model and its symmetries. With the help of the functional renormalization group I discuss the UV structure and possible condensation channels. I then reformulate the model in a partially bosonized language which is suitable for the investigation of dynamical mass generation.

05. 07. 2011 at 12:00
S2 11/207

Lunch Club Seminar

()
Thermodynamics of strong interactions from chiral models with Polyakov loop

28. 06. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Dr. Saori Pastore (Argonne National Laboratory)
Electromagnetic Structure of Light Nuclei From a Chiral EFT Perspective

We discuss the derivation of the two-nucleon electromagnetic charge and current operators carried out in a chiral effective field theory (EFT) with pions and nucleons as explicit degrees of freedom. We include corrections up to order e Q -- where Q denotes the low-momentum scale and e is the electric charge. A review of the results obtained within this framework for a number of electromagnetic observables induced by the magnetic dipole operator -- including the n-d and n-3He radiative captures at thermal neutron energies -- is presented.

21. 06. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Hiroaki Kohyama (Chung Yuan Christian University, Taiwan)
The effect of UA(1) anomaly restoration at high density in the Nambu Jona-Lasinio model

The UA(1) symmetry is broken due to the quantum effects. This plays a crucial role for low energy physics. The most important manifestation is the large mass of the eta prime meson which is comparable to the mass of the proton. It is expected that the UA(1) symmetry is restored at intermediate densities at which new states of quark matter such as color superconducting phases become dominant. In this talk, I consider the Nambu Jona-Lasinio model with UA(1) symmetry restoration at high density, and study the possible effect on meson properties and the QCD phase diagram.

14. 06. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Bardiya Bahrampour
Eichtheorie der elektroschwachen Wechselwirkung

07. 06. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Kurt Langfeld (University of Plymouth)
Fermi-Einstein Condensation

The empty vacuum of SU(N) Yang-Mills theories is reviewed. The "flat directions" of gauge inequivalent vacuum states collapse to a discrete Z(N) symmetry due to quantum fluctuations. The importance of centre-sector tunnelling for confinement is explained. The Z(N) centre symmetry is lifted by including dynamical matter such as quarks. It is shown that centre sector transitions still occur in the low temperature phase. The impact of these transitions in QCD and QCD-like theories is revealed: a new state of confined matter rises at low temperatures and intermediate values of the chemical potential when Fermi-Einstein condensation takes place. This new mechanism is explained in some detail.

31. 05. 2011 at 12:00
S2 11/207

Lunch Club Seminar

V. Sreekanth (Physical Research Laboratory Ahmedabad, India)
Viscosity and Thermal Dilepton Production in the QGP

We investigate the thermal dilepton production-rates using one dimensional
boost-invariant second order relativistic hydrodynamics to find proper
time evolution of the energy density and the temperature. We study the
non-ideal effects arising due to viscosity (both bulk and shear),
equation of state (epsilon - 3P) and cavitation on thermal dilepton
production from QGP at RHIC energies. The effect of bulk-viscosity and
non-ideal equation of state are taken into account in a manner consistent
with recent lattice QCD estimates. It is shown that the non-ideal
gas equation of state, i.e non-zero epsilon-3P, behavior of the expanding
plasma, which is important near the phase-transition point, can
significantly slow down the hydrodynamic expansion and thereby increase
the dilepton production-rates. We calculate the first order corrections to
the dilepton production rates due to shear and bulk viscosities. It is
shown that ignoring the cavitation can lead to a wrong estimation of the
particle spectra. We show that the shear viscosity can enhance the thermal
dilepton spectra whereas the bulk viscosity can suppress it. We present
the combined effect of bulk and shear viscosities on the dilepton spectra.

17. 05. 2011 at 12:00
S2 11/207

Lunch Club Seminar

Tomas Brauner ()
Two-color quark matter at nonzero temperature and density

03. 05. 2011 at 12:30
S2 11/207

Lunch Club Seminar

Florian Hebenstreit ()
Quantum kinetic of non-perturbative e^+e^- production - The influence of temporal and spatial inhomogeneities

Non-perturbative electron-positron pair creation in electric fields (Schwinger effect) has been a long-standing but still unobserved prediction of QED. Due to the advent of a new generation of high-intensity laser systems such as the European XFEL or the Extreme Light Infrastructure (ELI) it might, however, become possible to observe this effect within the next decades. Previous investigations led to a good understanding of the general mechanisms behind the pair creation process, however, realistic electric fields as they might be present in upcoming experiments have not been fully considered yet.


In this talk I focus on various aspects of the Schwinger effect in the presence of inhomogeneous electric fields: First, I consider the pair creation process in the presence of a spatially homogeneous, time-dependent electric field. Most notably, the momentum distribution of created particles in the presence of a pulsed electric field with sub-cycle structure, which serves as a simple model of the time-dependence of a realistic laser pulse, is presented. Moreover, I introduce a formalism by means of which the Schwinger effect in the presence of space- and time-dependent electric fields can be treated properly. Finally, I present the time evolution of various observable quantities (charge distribution, momentum spectrum, number of created particles) in the presence of a simple space- and time-dependent electric field which have been calculated for the first time.

25. 01. 2011 at 12:30
S2 11/207

Lunch Club Seminar

Ubirajara van Kolck (University of Arizona)
Time-Reversal Violation in the Nucleon and Light Nuclei

A new generation of experiments is being planned with a significant improvement in the sensitivity to electric dipole moments (EDMs) of the nucleon and light nuclei. Possible signals in any of these measurements would reflect time-reversal violation (TV) beyond that stemming from the phase of the CKM matrix. Could we then infer the origin of TV at the quark/gluon level?
I describe our on-going program to relate nucleon and light-nuclear TV observables to various TV sources, such as the QCD theta term, quark EDMs, quark and gluon color-EDMs, etc. We use the effective field theory of QCD that is applicable to hadronic momenta of order of the pion mass ---a generalization of chiral perturbation theory--- and can handle one- and many-nucleon physics consistently.

07. 12. 2010 at 12:30
S2 11/207

Lunch Club Seminar

Jeremy Holt ()
Chiral nuclear dynamics and applications with three-nucleon forces

30. 11. 2010 at 12:30
S2 11/207

Lunch Club Seminar

Lisa Marie Haas (Uni Heidelberg)
On the phase structure of two-flavour QCD

23. 11. 2010 at 12:30
S2 11/207

Lunch Club Seminar

Alexander E. Dorokhov (JINR, Dubna)
Current-current Correlators within the Nonlocal Chiral Quark Model

09. 11. 2010 at 12:30
S2 11/207

Lunch Club Seminar

Jens Andersen (University Trondheim)
Quasiparticles and hard-thermal-loop perturbation for a quark-gluon plasma

We calculate the thermodynamic functions of a quark-gluon plasma for general N_c and N_f to three-loop order using hard-thermal-loop perturbation theory. At this order, all the ultraviolet divergences can be absorbed into renormalizations of the vacuum, the HTL mass parameters, and the strong coupling constant.We show that at three loops, the results for the pressure and trace anomaly are in very good agreement with recent lattice data down to temperatures around 2T_c.

02. 11. 2010 at 12:30
S2 11/207

Lunch Club Seminar

David Weir (Imperial College London)
Non-perturbative notions of thickness

26. 10. 2010 at 12:30
S2 11/207

Lunch Club Seminar

Franziska Synatschke (Uni Jena)
Functional RG and Supersymmetry

Theories which allow for dynamical supersymmetry breaking have been subject to many investigations. But most approximations to solve these models break supersymmetry explicitly. The functional renormalization group equations allow an approach that leaves supersymmetry unbroken. A manifestly supersymmetric exact renormalization flow will be presented for a scalar theory in two dimensions. The considered model allows for dynamical supersymmetry breaking. The phase diagramm will be discussed as well as the fixed-point structure of the ERG flow which shows an interesting connection to the supersymmetry breaking.

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

Theorie-Seminar

on 07. 12. 2017 at 14:00
(S2 11/10)
Akaki Rusetsky
TBA
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