Kinetics of hydrodynamic pions in chiral perturbation theory

TL;DR

This paper calculates the kinetic coefficients of ultrasoft pions near the chiral limit using chiral perturbation theory, linking microscopic dynamics to hydrodynamic descriptions.

Contribution

It provides a leading order computation of axial charge diffusion and damping coefficients incorporating hard, soft, and ultrasoft pion modes.

Findings

Calculated kinetic coefficients for ultrasoft pions at finite temperature.

Connected microscopic kinetic theory with hydrodynamic effective descriptions.

Highlighted the importance of multiple pion mode scales in the dynamics.

Abstract

We determine the kinetic coefficients of ultrasoft pions using chiral perturbation theory at finite temperature close to the chiral limit. This is used to compute the axial charge diffusion and damping coefficients in the hydrodynamic effective theory for these pion waves. We show that to provide a leading order answer for these coefficients one needs to explore the dynamics of hard, soft, and ultrasoft pion modes, which are represented microscopically by the appropriate kinetic and hydrodynamic descriptions..