Study of the scalar and pseudoscalar meson mass spectrum above the QCD chiral phase transition, using an effective Lagrangian approach

TL;DR

This study uses an effective Lagrangian to analyze the scalar and pseudoscalar meson mass spectrum above the QCD chiral transition temperature, comparing predictions with lattice QCD results to explore $U(1)$ axial symmetry breaking.

Contribution

It provides a detailed effective Lagrangian model for meson masses at finite temperature in a realistic three-flavor scenario, focusing on symmetry restoration and breaking above $T_c$.

Findings

Model predictions align with lattice QCD results for meson screening masses.

Evidence suggests partial restoration of chiral symmetry above $T_c$.

Signatures of $U(1)$ axial symmetry breaking are analyzed in the meson spectrum.

Abstract

In this work, expanding on previous analyses, we employ an effective Lagrangian approach to investigate the mass spectrum of scalar and pseudoscalar mesons at finite temperature, above the (pseudo-)critical temperature $T_c$, in a "realistic" $N_f = 2 + 1$ flavor scenario with degenerate $up$ and $down$ quarks and a heavier $strange$ quark: $0 < m_u = m_d \ll m_s$. The model's predictions are then critically compared with available lattice QCD results (where meson screening masses are extracted from chiral susceptibilities, which correspond to two-point correlation functions of suitable interpolating operators), looking, in particular, for signatures of the breaking of the $U(1)$ axial symmetry above $T_c$.