Spectral properties of pseudo-scalar mesons through the QCD 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.