Light quarks at finite temperature: chiral restoration and the fate of the $U(1)_A$ symmetry

TL;DR

This paper reviews how light quark states influence the QCD phase diagram, focusing on chiral and $U(1)_A$ symmetry restoration at finite temperature through theoretical and lattice methods.

Contribution

It integrates effective theories, unitarization, and Ward identities to analyze chiral symmetry restoration and the role of scalar mesons in the QCD phase transition.

Findings

Light scalar mesons are key to understanding susceptibilities related to symmetry restoration.

Theoretical techniques align with lattice results on chiral and $U(1)_A$ symmetry behavior.

Chiral and $U(1)_A$ partner interactions are crucial for transition pattern analysis.

Abstract

We review recent results on the role of light quark states within the QCD phase diagram. In particular, we will discuss how the combined use of theoretical techniques such as Effective Theories, Unitarization and Ward Identities helps to shed light on several important issues regarding chiral symmetry restoration, building bridges with recent lattice analyses. Special attention will be paid to the role of chiral and $U(1)_A$ partners in the interplay between those symmetries, which is crucial to properly understand the transition pattern. Light scalar mesons at finite temperature will be shown to be responsible for the description of susceptibilities encoding chiral and $U(1)_A$ restoration properties.