58 research outputs found
Remarks concerning bulk viscosity of hadron matter in relaxation time ansatz
The bulk viscosity is calculated for hadron matter produced in heavy-ion
collisions, being described in the relaxation time approximation withi n the
relativistic mean- field-based model with scaled hadron masses and couplings. W
e show how different approximations used in the literature affect the result.
Nume rical evaluations of the bulk viscosity with three considered models
deviate not much from each other confirming earlier results.Comment: 17 pages, 3 figure
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
Baryon Stopping in Heavy-Ion Collisions at E_{lab}= 2--160 GeV/nucleon
It is argued that the experimentally observed baryon stopping may indicate
(within the present experimental uncertainties) a non-monotonous behaviour as a
function of the incident energy of colliding nuclei. This can be quantified by
a midrapidity reduced curvature of the net-proton rapidity spectrum. The above
non-monotonous behaviour reveals itself as a "zig-zag" irregularity in the
excitation function of this curvature. The three-fluid dynamic calculations
with a hadronic equation of state (EoS) fail to reproduce this irregularity. At
the same time, the same calculations with an EoS involving a first-order phase
transition into the quark-gluon phase do reproduce this "zig-zag" behaviour,
however only qualitatively.Comment: 6 pages, 5 figures, the paper is essentially extended. This version
will be published in Phys. Lett.
Fractional exclusion statistics applied to relativistic nuclear matter
The effect of statistics of the quasiparticles in the nuclear matter at
extreme conditions of density and temperature is evaluated in the relativistic
mean-field model generalized to the framework of the fractional exclusion
statistics (FES). In the model, the nucleons are described as quasiparticles
obeying FES and the model parameters were chosen to reproduce the ground state
properties of the isospin-symmetric nuclear matter. In this case, the
statistics of the quasiparticles is related to the strengths of the
nucleon-nucleon interaction mediated by the neutral scalar and vector meson
fields. The relevant thermodynamic quantities were calculated as functions of
the nucleons density, temperature and fractional exclusion statistics parameter
. It has been shown that at high temperatures and densities the
thermodynamics of the system has a strong dependence on the statistics of the
particles. The scenario in which the nucleon-nucleon interaction strength is
independent of the statistics of particles was also calculated, but it leads in
general to unstable thermodynamics.Comment: 17 pages, 7 figure
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