Spectral properties of pseudo-scalar mesons through the QCD chiral crossover

TL;DR

This paper reviews recent non-perturbative methods to determine thermal spectral functions of pseudo-scalar mesons in QCD, highlighting the dominance of vacuum-like excitations and the persistence of resonance structures near the chiral crossover.

Contribution

It introduces a framework leveraging micro-causality constraints to analyze lattice correlators and describe meson spectral functions near the QCD chiral crossover.

Findings

Negligible scattering, Landau damping, and collective excitations above certain temperatures.

Quantitative match of lattice correlators with thermoparticle models.

Resonance-like structures persist above the chiral crossover.

Abstract

We summarise recent progress towards the non-perturbative determination of thermal spectral functions for pseudo-scalar mesons in QCD by exploiting constraints imposed by micro-causality at finite temperature. For temperatures not much above the vacuum particle mass, continuous contributions from scattering, Landau damping and collective excitations are found to be negligible. This allows for a quantitative description of spatial and temporal lattice correlators in terms of thermoparticles, i.e.~vacuum excitations modified by medium effects, with resonance-like structures persisting for a range above the chiral crossover.