Comments on the U(1) axial symmetry and the chiral transition in QCD

TL;DR

This paper investigates the behavior of scalar and pseudoscalar meson masses in QCD at finite temperature, focusing on the potential breaking of U(1) axial symmetry above the chiral transition, using a chiral effective Lagrangian model.

Contribution

It provides a comparative analysis of U(1) axial symmetry restoration in QCD for different numbers of light quark flavors using an effective Lagrangian approach.

Findings

Identifies signatures of U(1) axial symmetry breaking above T_c.

Highlights differences in meson spectra for N_f=2 and N_f≥3.

Uses a chiral effective Lagrangian to analyze finite temperature effects.

Abstract

We analyze (using a chiral effective Lagrangian model) the scalar and pseudoscalar meson mass spectrum of QCD at finite temperature, above the chiral transition at $T_c$, looking, in particular, for signatures of a possible breaking of the $U(1)$ axial symmetry above $T_c$. A detailed comparison between the case with a number of light quark flavors $N_f\geq 3$ and the (remarkably different) case $N_f=2$ is performed.