Transport coefficients of a massive pion gas

TL;DR

This paper reviews the transport coefficients of a massive pion gas, presenting leading order results for various conductivities and viscosities, and discusses their theoretical implications near the QCD phase transition.

Contribution

It provides the first comprehensive leading order calculations of transport coefficients specifically for a massive pion gas within chiral perturbation theory.

Findings

Electrical and thermal conductivities are quantified at leading order.

Shear and bulk viscosities are calculated, highlighting their behavior near phase transition.

A potential link between bulk viscosity and QCD trace anomaly is discussed.

Abstract

We review or main results concerning the transport coefficients of a light meson gas, in particular we focus on the case of a massive pion gas. Leading order results according to the chiral power-counting are presented for the DC electrical conductivity, thermal conductivity, shear viscosity, and bulk viscosity. We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD, as well as the relation between unitarity and a minimum of the quotient $\eta/s$ near the phase transition.