35 research outputs found
Relativistic Mean-Field Model with Scaled Hadron Masses and Couplings
Here we continue to elaborate properties of the relativistic mean-field based
model (SHMC) proposed in ref. [6] where hadron masses and coupling constants
depend on the -meson field. The validity of approximations used in [6]
is discussed. We additionally incorporate contribution of meson excitations to
the equations of motion. We also estimate the effects of the particle width. It
is demonstrated that the inclusion of the baryon-baryon hole and
baryon-antibaryon loop terms, if performed perturbatively, destroys the
consistency of the model.Comment: 44 pages, 14 figures; corrected according to referee's remarks,
version accepted for publication in Nucl. Phys.
Viscosity coefficients for hadron and quark-gluon phases
The shear () and bulk () viscosities are calculated in a
quasiparticle relaxation time approximation. The hadron phase is described
within the relativistic mean field based model with scaled hadron masses and
couplings. The quark phase is treated in terms of the heavy quark bag model
fitted to the lattice data. A two-phase model allowing for the first order
phase transition from the hadron phase to the strongly coupled quark gluon
plasma is constructed by means of the Gibbs conditions. Temperature and baryon
density dependence of the calculated viscosity-to-entropy ratios (,
) are analyzed and compared with those obtained in other models.
Special attention is paid to the behavior of viscosity coefficients near the
critical temperature, from both hadron and quark-gluon side. Effects of
resonance widths on viscosities and viscosity-to-entropy ratios are estimated.Comment: 56 pages, 22 figure
Viscosity of hadron matter within relativistic mean-field based model with scaled hadron masses and couplings
The shear () and bulk () viscosities are calculated in a
quasiparticle relaxation time approximation for a hadron matter described
within the relativistic mean-field based model with scaled hadron masses and
couplings. Comparison with results of other models is presented. We demonstrate
that a small value of the shear viscosity to entropy density ratio required for
explaining a large elliptic flow observed at RHIC may be reached in the hadron
phase. Large values of the bulk viscosity are noted in case of the baryon
enriched matter.Comment: 16 pages, 6 figures; minor clarifying change
Shear and bulk viscosities for pure glue matter
Shear and bulk viscosities are calculated in a quasiparticle
model within a relaxation time approximation for pure gluon matter. Below
the confined sector is described within a quasiparticle glueball model.
Particular attention is paid to behavior of the shear and bulk viscosities near
. The constructed equation of state reproduces the first-order phase
transition for the glue matter. It is shown that with this equation of state it
is possible to describe the temperature dependence of the shear viscosity to
entropy ratio and the bulk viscosity to entropy ratio in
reasonable agreement with available lattice data but absolute values of the
ratio underestimate the upper limits of this ratio in the lattice
measurements typically by an order of magnitude.Comment: 8 pages, 4 figures; the published versio
Lattice QCD Constraints on the Nuclear Equation of State
Based on the quasi-particle description of the QCD medium at finite
temperature and density we formulate the phenomenological model for the
equation of state that exhibits crossover or the first order deconfinement
phase transition. The models are constructed in such a way to be
thermodynamically consistent and to satisfy the properties of the ground state
nuclear matter comply with constraints from intermediate heavy--ion collision
data. Our equations of states show quite reasonable agreement with the recent
lattice findings on temperature and baryon chemical potential dependence of
relevant thermodynamical quantities in the parameter range covering both the
hadronic and quark--gluon sectors. The model predictions on the isentropic
trajectories in the phase diagram are shown to be consistent with the recent
lattice results. Our nuclear equations of states are to be considered as an
input to the dynamical models describing the production and the time evolution
of a thermalized medium created in heavy ion collisions in a broad energy range
from SIS up to LHC.Comment: 13 pages, 11 figure
Lattice QCD Constraints on Hybrid and Quark Stars
A QCD-motivated dynamical-quasiparticle model with parameters adjusted to
reproduce the lattice-QCD equation of state is extrapolated from region of high
temperatures and moderate baryonic densities to the domain of high baryonic
densities and zero temperature. The resulting equation of state matched with
realistic hadronic equations of state predicts a phase transition into the
quark phase at higher densities than those reachable in neutron star interiors.
This excludes the possibility of the existence of hybrid (hadron-quark) stars.
Pure quark stars are possible and have low masses, small radii and very high
central densities. Similar results are obtained for a simple bag model with
massive quarks, fitted to reproduce the same lattice results. Self-bound quark
matter is also excluded within these models. Uncertainties in the present
extrapolation re discussed. Comparison with standard bag models is made.Comment: 13 p., 8 figs., 7 tables, Version accepted by Phys. Rev.
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