Transport properties of a meson gas

TL;DR

This paper develops a systematic method within Chiral Perturbation Theory to calculate transport coefficients of a meson gas, analyzing their temperature dependence and fundamental properties relevant to heavy-ion collisions.

Contribution

It introduces a novel approach that incorporates particle collision effects via a non-zero width in Feynman diagrams, aligning with kinetic theory results at leading order.

Findings

Bulk viscosity is negligible near the chiral phase transition.

Electrical and thermal conductivities increase with temperature.

Shear viscosity dominates over bulk viscosity in the studied regime.

Abstract

We present recent results on a systematic method to calculate transport coefficients for a meson gas (in particular, we analyze a pion gas) at low temperatures in the context of Chiral Perturbation Theory. Our method is based on the study of Feynman diagrams with a power counting which takes into account collisions in the plasma by means of a non-zero particle width. In this way, we obtain results compatible with analysis of Kinetic Theory with just the leading order diagram. We show the behavior with temperature of electrical and thermal conductivities and shear and bulk viscosities, and we discuss the fundamental role played by unitarity. We obtain that bulk viscosity is negligible against shear viscosity near the chiral phase transition. Relations between the different transport coefficients and bounds on them based on different theoretical approximations are also discussed. We also comment on some applications to heavy-ion collisions.