The chiral transition and U(1)_A symmetry restoration from lattice QCD using Domain Wall Fermions

TL;DR

This study investigates the restoration of chiral and U(1)_A symmetries in finite temperature QCD using lattice simulations with domain wall fermions, analyzing various susceptibilities and eigenvalue spectra across a temperature range.

Contribution

It provides new lattice QCD results on chiral and U(1)_A symmetry restoration at finite temperature with physical quark masses using domain wall fermions.

Findings

Chiral symmetry is restored near T = 150 MeV.

U(1)_A symmetry shows effective restoration above T = 160 MeV.

Eigenvalue spectrum indicates symmetry restoration at high temperatures.

Abstract

We present results on both the restoration of the spontaneously broken chiral symmetry and the effective restoration of the anomalously broken U(1)_A symmetry in finite temperature QCD at zero chemical potential using lattice QCD. We employ domain wall fermions on lattices with fixed temporal extent N_\tau = 8 and spatial extent N_\sigma = 16 in a temperature range of T = 139 - 195 MeV, corresponding to lattice spacings of a \approx 0.12 - 0.18 fm. In these calculations, we include two degenerate light quarks and a strange quark at fixed pion mass m_\pi = 200 MeV. The strange quark mass is set near its physical value. We also present results from a second set of finite temperature gauge configurations at the same volume and temporal extent with slightly heavier pion mass. To study chiral symmetry restoration, we calculate the chiral condensate, the disconnected chiral susceptibility, and susceptibilities in several meson channels of different quantum numbers. To study U(1)_A restoration, we calculate spatial correlators in the scalar and pseudo-scalar channels, as well as the corresponding susceptibilities. Furthermore, we also show results for the eigenvalue spectrum of the Dirac operator as a function of temperature, which can be connected to both U(1)_A and chiral symmetry restoration via Banks-Casher relations.