2,438 research outputs found
The renormalization group and quark number fluctuations in the Polyakov loop extended quark-meson model at finite baryon density
Thermodynamics and the phase structure of the Polyakov loop-extended two
flavors chiral quark--meson (PQM) model is explored beyond the mean-field
approximation. The analysis of the PQM model is based on the functional
renormalization group (FRG) method. We formulate and solve the renormalization
group flow equation for the scale-dependent thermodynamic potential in the
presence of the gluonic background field at finite temperature and density. We
determine the phase diagram of the PQM model in the FRG approach and discuss
its modification in comparison with the one obtained under the mean-field
approximation. We focus on properties of the net-quark number density
fluctuations as well as their higher moments and discuss the influence of
non-perturbative effects on their properties near the chiral crossover
transition. We show, that with an increasing net-quark number density the
higher order moments exhibit a peculiar structure near the phase transition. We
also consider ratios of different moments of the net-quark number density and
discuss their role as probes of deconfinement and chiral phase transitions
Thermodynamic limit and semi--intensive quantities
The properties of statistical ensembles with abelian charges close to the
thermodynamic limit are discussed. The finite volume corrections to the
probability distributions and particle density moments are calculated. Results
are obtained for statistical ensembles with both exact and average charge
conservation. A new class of variables (semi--intensive variables) which differ
in the thermodynamic limit depending on how charge conservation is implemented
in the system is introduced. The thermodynamic limit behavior of these
variables is calculated through the next to leading order finite volume
corrections to the corresponding probability density distributions.Comment: 11 pages, 2 figures In v2 figures are added and corresponding
editorial changes are done. Paper will be published in Journal of Physics
The QCD equation of state for two flavours at non-zero chemical potential
We present results of a simulation of 2 flavour QCD on a
lattice using p4-improved staggered fermions with bare quark mass .
Derivatives of the thermodynamic grand canonical partition function
with respect to chemical potentials for
different quark flavours are calculated up to sixth order, enabling estimates
of the pressure and the quark number density as well as the chiral condensate
and various susceptibilities as functions of via Taylor series
expansion. Results are compared to high temperature perturbation theory as well
as a hadron resonance gas model. We also analyze baryon as well as isospin
fluctuations and discuss the relation to the chiral critical point in the QCD
phase diagram. We moreover discuss the dependence of the heavy quark free
energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes
The canonical partition function for relativistic hadron gases
Particle production in high-energy collisions is often addressed within the
framework of the thermal (statistical) model. We present a method to calculate
the canonical partition function for the hadron resonance gas with exact
conservation of the baryon number, strangeness, electric charge, charmness and
bottomness. We derive an analytical expression for the partition function which
is represented as series of Bessel functions. Our results can be used directly
to analyze particle production yields in elementary and in heavy ion
collisions. We also quantify the importance of quantum statistics in the
calculations of the light particle multiplicities in the canonical thermal
model of the hadron resonance gas.Comment: 10 pages, 2 figures; submitted for publication in EPJ
Unified Description of Freeze-Out Parameters in Relativistic Heavy Ion Collisions
It is shown that the chemical freeze-out parameters obtained at CERN/SPS,
BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV per
hadron in the local rest frame of the system, independent of the beam energy
and of the target and beam particles.Comment: revtex, 1 figur
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