3,442 research outputs found
Kurtosis and compressibility near the chiral phase transition
The properties of net quark number fluctuations in the vicinity of the QCD
chiral phase transition are discussed in terms of an effective chiral model in
the mean-field approximation. We focus on the ratio of the fourth- to second-
order cumulants (kurtosis) and the compressibility of the system and discuss
their dependence on the pion mass. It is shown that near the chiral phase
transition, both observables are sensitive to the value of . For
physical , the kurtosis exhibits a peak whereas the inverse
compressibility shows a dip at the pseudocritical temperature. These structures
disappear for large . Our results, obtained in an effective model with
two flavors, are qualitatively consistent with recent results of 2+1 flavor
lattice gauge theory. We also discuss the high- and low-temperature properties
of these observables and the role of the coupling of the quark degrees of
freedom to the Polyakov loop
Susceptibilities and the Phase Structure of a Chiral Model with Polyakov Loops
In an extension of the Nambu-Jona-Lasinio model where the quarks interact
with the temporal gluon field, represented by the Polyakov loop, we explore the
relation between the deconfinement and chiral phase transitions. The effect of
Polyakov loop dynamics on thermodynamic quantities, on the phase structure at
finite temperature and baryon density and on various susceptibilities is
presented. Particular emphasis is put on the behavior and properties of the
fluctuations of the (approximate) order parameters and their dependence on
temperature and net--quark number density. We also discuss how the phase
structure of the model is influenced by the coupling of the quarks to the
Polyakov loop.Comment: 18 pages, 22 figures; text rearranged and references added. results
and conclusions unchanged; final version accepted for publication in Phys.
Rev.
Shear and bulk viscosities of the gluon plasma in a quasiparticle description
Shear and bulk viscosities of deconfined gluonic matter are investigated
within an effective kinetic theory by describing the strongly interacting
medium phenomenologically in terms of quasiparticle excitations with
medium-dependent self-energies. We show that the resulting transport
coefficients reproduce the parametric dependencies on temperature and coupling
obtained in perturbative QCD at large temperatures and small running coupling.
The extrapolation into the non-perturbative regime results in a decreasing
specific shear viscosity with decreasing temperature, exhibiting a minimum in
the vicinity of the deconfinement transition, while the specific bulk viscosity
is sizeable in this region falling off rapidly with increasing temperature. The
temperature dependence of specific shear and bulk viscosities found within this
quasiparticle description of the pure gluon plasma is in agreement with
available lattice QCD results.Comment: Sep 2011. 24pp. 6 figures. revised journal versio
Effective chiral model with Polyakov loops and its application to hot/dense medium
We study the thermodynamics of the Nambu--Jona-Lasinio model with Polyakov
loops, where spontaneous chiral symmetry breaking and confinement are taken
into account. We focus on the phase structure of the model and explore the
susceptibilities associated with corresponding order parameters under the
mean-field approximation.Comment: 4 pages, 1 figure, to appear in the proceedings of the Yukawa
International Seminars (YKIS) 2006, Nov.27-Dec.1, 2006, Kyoto, Japa
Viscosities in the Gluon-Plasma within a Quasiparticle Model
A phenomenological quasiparticle model, featuring dynamically generated
self-energies of excitation modes, successfully describes lattice QCD results
relevant for the QCD equation of state and related quantities both at zero and
non-zero net baryon density. Here, this model is extended to study bulk and
shear viscosities of the gluon-plasma within an effective kinetic theory
approach. In this way, the compatibility of the employed quasiparticle ansatz
with the apparent low viscosities of the strongly coupled deconfined gluonic
medium is shown.Comment: 4 pages, 1 figure. To appear in the conference proceedings for Quark
Matter 2009, March 30 - April 4, Knoxville, Tennessee, US
Susceptibilities and the Phase Structure of an Effective Chiral Model with Polyakov Loops
In the Nambu--Jona-Lasinio model with Polyakov loops, we explore the relation
between the deconfinement and chiral phase transitions within the mean-field
approximation. We focus on the phase structure of the model and study the
susceptibilities associated with corresponding order parameters.Comment: 6 pages, 2 figures, contribution to the proceedings of the 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(QM2006), November 14-20 2006, Shanghai, Chin
Transport Coefficients in Gluodynamics: From Weak Coupling towards the Deconfinement Transition
We study the ratio of bulk to shear viscosity in gluodynamics within a
phenomenological quasiparticle model. We show that at large temperatures this
ratio exhibits a quadratic dependence on the conformality measure as known from
weak coupling perturbative QCD. In the region of the deconfinement transition,
however, this dependence becomes linear as known from specific strongly coupled
theories. The onset of the strong coupling behavior is located near the maximum
of the scaled interaction measure. This qualitative behavior of the viscosity
ratio is rather insensitive to details of the equation of state.Comment: Oct 2011. 3 pages. 3 figures. Contribution to the proceedings of the
19th Particles and Nuclei International Conference (PANIC11
Vacuum fluctuations and the thermodynamics of chiral models
We consider the thermodynamics of chiral models in the mean-field
approximation and discuss the relevance of the (frequently omitted) fermion
vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended
version, we show that the fermion vacuum fluctuations can change the order of
the phase transition in the chiral limit and strongly influence physical
observables. We compute the temperature-dependent effective potential and
baryon number susceptibilities in these models, with and without the vacuum
term, and explore the cutoff and the pion mass dependence of the
susceptibilities. Finally, in the renormalized model the divergent vacuum
contribution is removed using the dimensional regularization.Comment: 9 pages, 5 figure
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