Chiral Relaxation Time at the Crossover of Quantum Chromodynamics

TL;DR

This paper investigates the microscopic processes responsible for chirality flips in QCD near the crossover temperature, using a Nambu-Jona-Lasinio model to estimate the chiral relaxation time, which is found to be around 0.1 to 1 fm/c.

Contribution

It introduces a detailed calculation of chiral relaxation time at the QCD crossover using a NJL model and pion/$\sigma$-meson exchange processes.

Findings

Chiral relaxation time is approximately 0.1 to 1 fm/c near the crossover.

Quark-quark scatterings mediated by pions and sigma mesons dominate chirality flips.

The model provides a microscopic estimate relevant for understanding chiral dynamics in QCD.

Abstract

We study microscopic processes responsible for chirality flips in the thermal bath of Quantum Chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely $T \simeq (150, 200)$ MeV. The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and $\sigma$-meson, hence we refer to these processes simply as \sugg{to} one-pion (one-$\sigma$) exchange\sugg{s}. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time $\tau$. We find $\tau\simeq 0.1 \div 1$ fm/c around the chiral crossover.