Bulk and shear viscosities of hot and dense hadron gas

TL;DR

This paper estimates the bulk and shear viscosities of hot, dense hadron gas using theoretical models, revealing how these viscosities vary with temperature and chemical potential, which is crucial for understanding hadronic matter in extreme conditions.

Contribution

It introduces a novel estimation of bulk and shear viscosities of hadron gas at finite temperature and baryon density using QCD theorems and kinetic theory, highlighting their dependence on chemical potential.

Findings

Bulk viscosity to entropy ratio increases with chemical potential.

Shear viscosity to entropy ratio decreases at low temperatures and increases at high temperatures with chemical potential.

Viscosity ratios are related to changes in sound velocity and entropy density under varying conditions.

Abstract

We estimate bulk and shear viscosity at finite temperature and baryon densities of hadronic matter within hadron resonance gas model. For bulk viscosity we use low energy theorems of QCD for the energy momentum tensor correlators. For shear viscosity coefficient, we estimate the same using molecular kinetic theory to relate the shear viscosity coefficient to average momentum of the hadrons in the hot and dense hadron gas. The bulk viscosity to entropy ratio increases with chemical potential and is related to the reduction of velocity of sound at nonzero chemical potential. The shear viscosity to entropy ratio on the other hand, shows a nontrivial behavior with the ratio decreasing with chemical potential for small temperatures but increasing with chemical potential at high temperatures and is related to decrease of entropy density with chemical potential at high temperature due to finite volume of the hadrons.