Chiral symmetry breaking and chemical equilibrium in a heavy-ion collisions

TL;DR

This paper investigates how pseudoscalar mesons thermalize in heavy-ion collisions, revealing that due to their nature as pseudo-Goldstone bosons, they take a long time to reach equilibrium, affecting chemical equilibrium in the resulting fireballs.

Contribution

It models meson interactions constrained by chiral symmetry and unitarity, demonstrating the prolonged thermalization times in heavy-ion collision environments.

Findings

Mesons take a very long time to thermalize.

Long relaxation times are linked to chiral symmetry breaking.

Fireballs lose chemical equilibrium upon entering the broken phase.

Abstract

We examine the thermalization of an ensemble of the octet of pseudoscalar mesons, in the isospin symmetric limit, whose interactions are constrained through chiral symmetry, unitarity, and measurements. The reaction amplitudes generate all resonances up to masses of about 2 GeV, with twelve input parameters, namely f_pi, three masses, and eight low energy constants (LECs) of chiral perturbation theory. In linear response theory, we find that matter takes an extremely long time to thermalize. These long relaxation times are directly related to the fact that these mesons are pseudo-Goldstone bosons of chiral symmetry breaking. This result indicates that fireballs created with zero baryon number in heavy-ion collisions will drop out of chemical equilibrium once they enter the chiral symmetry broken phase.