Medium effects on the viscosities of a pion gas

TL;DR

This paper calculates the bulk and shear viscosities of a pion gas considering in-medium effects and chemical freeze-out, revealing significant impacts on their temperature dependence.

Contribution

It introduces in-medium modifications to the $ ho$ and $\sigma$ meson propagators in viscosity calculations of a pion gas, incorporating chemical freeze-out effects.

Findings

In-medium effects significantly alter viscosity temperature dependence.

Chemical freeze-out influences bulk and shear viscosities.

Viscosity calculations align with heavy ion collision conditions.

Abstract

The bulk and shear viscosities of a pion gas is obtained by solving the relativistic transport equation in the Chapman-Enskog approximation. In-medium effects are introduced in the $\pi\pi$ cross-section through one-loop self-energies in the propagator of the exchanged $\rho$ and $\sigma$ mesons. The effect of early chemical freeze-out in heavy ion collisions is implemented through a temperature dependent pion chemical potential. These are found to affect the temperature dependence of the bulk and shear viscosities significantly.