The QCD chiral transition, $\ua$ symmetry and the Dirac spectrum using domain wall fermions

TL;DR

This study investigates the finite-temperature QCD transition, chiral symmetry restoration, and the Dirac spectrum using domain wall fermions, revealing a pseudo-critical temperature around 165 MeV and evidence of U(1)_A symmetry breaking above T_c.

Contribution

The paper provides a detailed lattice QCD analysis of chiral and axial symmetry behaviors across the transition using improved fermion formulations and larger volumes.

Findings

Pseudo-critical temperature T_c ≈ 165 MeV

Strong finite volume effects below T_c

Evidence of U(1)_A symmetry breaking above T_c

Abstract

We report on a study of the finite-temperature QCD transition region for temperatures between 139 and 196 MeV, with a pion mass of 200 MeV and two space-time volumes: $24^3\times8$ and $32^3\times8$, where the larger volume varies in linear size between 5.6 fm (at T=139 MeV) and 4.0 fm (at T=195 MeV). These results are compared with the results of an earlier calculation using the same action and quark masses but a smaller, $16^3\times8$ volume. The chiral domain wall fermion formulation with a combined Iwasaki and dislocation suppressing determinant ratio gauge action are used. This lattice action accurately reproduces the $\sua$ and $\ua$ symmetries of the continuum. Results are reported for the chiral condensates, connected and disconnected susceptibilities and the Dirac eigenvalue spectrum. We find a pseudo-critical temperature, $T_c$, of approximately 165 MeV consistent with previous results and strong finite volume dependence below $T_c$. Clear evidence is seen for $\ua$ symmetry breaking above $T_c$ which is quantitatively explained by the measured density of near-zero modes in accordance with the dilute instanton gas approximation.