40 research outputs found
Worldline Monte Carlo for fermion models at large N_f
Strongly-coupled fermionic systems can support a variety of low-energy
phenomena, giving rise to collective condensation, symmetry breaking and a rich
phase structure. We explore the potential of worldline Monte Carlo methods for
analyzing the effective action of fermionic systems at large flavor number N_f,
using the Gross-Neveu model as an example. Since the worldline Monte Carlo
approach does not require a discretized spacetime, fermion doubling problems
are absent, and chiral symmetry can manifestly be maintained. As a particular
advantage, fluctuations in general inhomogeneous condensates can conveniently
be dealt with analytically or numerically, while the renormalization can always
be uniquely performed analytically. We also critically examine the limitations
of a straightforward implementation of the algorithms, identifying potential
convergence problems in the presence of fermionic zero modes as well as in the
high-density region.Comment: 40 pages, 13 figure
Shear viscosity of the Quark-Gluon Plasma from a virial expansion
We calculate the shear viscosity in the quark-gluon plasma (QGP) phase
within a virial expansion approach with particular interest in the ratio of
to the entropy density , i.e. . The virial expansion approach
allows us to include the interactions between the partons in the deconfined
phase and to evaluate the corrections to a single-particle partition function.
In the latter approach we start with an effective interaction with parameters
fixed to reproduce thermodynamical quantities of QCD such as energy and/or
entropy density. We also directly extract the effective coupling \ga_{\rm V}
for the determination of . Our numerical results give a ratio
at the critical temperature , which is very
close to the theoretical bound of . Furthermore, for temperatures
the ratio is in the range of the present
experimental estimates at RHIC. When combining our results for
in the deconfined phase with those from chiral perturbation theory or
the resonance gas model in the confined phase we observe a pronounced minimum
of close to the critical temperature .Comment: Published in Eur. Phys. J. C, 7 pages, 2 figures, 3 tabl
Hydrodynamic Modeling and the QGP Shear Viscosity
In this article, we will briefly review the recent progress on hydrodynamic
modeling and the extraction of the quark-gluon plasma (QGP) specific shear
viscosity with an emphasis on results obtained from the hybrid model VISHNU
that couples viscous hydrodynamics for the macroscopic expansion of the QGP to
the hadron cascade model for the microscopic evolution of the late hadronic
stage.Comment: 10 pages, 4 figures, EPJA: Topical issue on "Relativistic Hydro- and
Thermodynamics