Thermal hadron resonances in chiral and $U(1)_A$ restoration

TL;DR

This paper reviews how thermal hadron resonances relate to chiral and $U(1)_A$ symmetry restoration in QCD, using unitarized chiral perturbation theory to connect scattering states with phase transition phenomena.

Contribution

It demonstrates the use of unitarized ChPT to analyze scalar resonances and their role in understanding chiral and $U(1)_A$ restoration at finite temperature.

Findings

Scalar susceptibilities describe resonance behavior at finite temperature

Chiral and $U(1)_A$ restoration are interconnected through Ward Identities

Scalar resonances provide insights into the QCD phase transition

Abstract

We review recent work on thermal resonances and their connection with chiral symmetry and $U(1)_A$ restoration within the QCD phase diagram. In particular, the $f_0(500)$ and $K_0^* (700)$ states generated from $\pi\pi$ and $\pi K$ scattering within Unitarized Chiral Perturbation Theory (ChPT) at finite temperature allow one to describe scalar susceptibilities, which combined with Ward Identities yield interesting conclusions regarding the interplay between chiral and $U(1)_A$ restoration, key to understand the nature of the transition