Axial $U(1)$ symmetry at high temperature in 2-flavor lattice QCD

TL;DR

This study examines the behavior of axial U(1) symmetry in two-flavor lattice QCD at high temperatures, finding evidence of symmetry restoration in the chiral limit and its relation to topological susceptibility.

Contribution

It provides new lattice QCD results on U(1)_A symmetry restoration above the critical temperature using dynamical fermion ensembles.

Findings

U(1)_A symmetry is restored at T=220 MeV in the chiral limit.

U(1)_A susceptibility vanishes with topological susceptibility.

Results suggest symmetry restoration coincides with topological susceptibility reduction.

Abstract

We investigate the axial $U(1)_A$ symmetry breaking above the critical temperature in two-flavor lattice QCD. The ensembles are generated with dynamical M\"obius domain-wall or reweighted overlap fermions. The $U(1)_A$ susceptibility is extracted from the low-modes spectrum of the overlap Dirac eigenvalues. We show the quark mass and temperature dependences of $U(1)_A$ susceptibility. Our results at $T=220 \, \mathrm{MeV}$ imply that the $U(1)_A$ symmetry is restored in the chiral limit. Its coincidence with vanishing topological susceptibility is observed.