Aspects of chiral symmetry in QCD at T=128 MeV

Abstract

We investigate several aspects of chiral symmetry in QCD at a temperature of $T=128\text{ }\text{ }\mathrm{MeV}$. The study is based on a $24\ifmmode\times\else\texttimes\fi{}9{6}^{3}$ lattice-QCD ensemble with $\mathrm{O}(a)$-improved Wilson quarks and physical up, down and strange quark masses. The pion quasiparticle turns out to be significantly lighter than the zero-temperature pion mass, even though the corresponding static correlation length is shorter. We perform a quantitative comparison of our findings to predictions of chiral perturbation theory. Among several order parameters for chiral symmetry restoration, we compute the difference of the vector- and axial-vector time-dependent correlators and find it to be reduced by a factor $\ensuremath{\sim}2/3$ as compared to its vacuum counterpart.