Viscosity coefficients for hadron and quark-gluon phases

TL;DR

This paper calculates shear and bulk viscosities in hadron and quark-gluon phases using quasiparticle models, analyzing their temperature and density dependence near the phase transition, and compares results with other models.

Contribution

It introduces a two-phase model with a first order phase transition, incorporating resonance widths and comparing viscosity ratios across phases.

Findings

Viscosity-to-entropy ratios vary with temperature and density.

Viscosities exhibit characteristic behavior near the critical temperature.

Resonance widths significantly affect viscosity calculations.

Abstract

The shear ($\eta$) and bulk ($\zeta$) 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 ($\eta/s$, $\zeta/s$) 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.