Study of the axial U(1) anomaly at high temperature with lattice chiral fermions

TL;DR

This study uses advanced lattice QCD techniques to examine the axial U(1) anomaly at high temperatures, finding evidence that the anomaly effectively disappears above the critical temperature, consistent with chiral symmetry restoration.

Contribution

It employs improved lattice actions and larger volumes to precisely analyze the U(1) anomaly's behavior at high temperatures, including the chiral limit.

Findings

U(1) anomaly effects are consistent with zero above critical temperature.

The U(1) anomaly disappearance rate matches chiral symmetry restoration.

Finite size effects are carefully estimated with larger volumes.

Abstract

We investigate the axial U(1) anomaly of two-flavor QCD at temperatures 190--330 MeV. In order to preserve precise chiral symmetry on the lattice, we employ the Mobius domain-wall fermion action as well as overlap fermion action implemented with a stochastic reweighting technique. Compared to our previous studies, we reduce the lattice spacing to 0.07 fm, simulate larger multiple volumes to estimate finite size effect, and take more than four quark mass points, including one below physical point to investigate the chiral limit. We measure the topological susceptibility, axial U(1) susceptibility, and examine the degeneracy of U(1) partners in meson and baryon correlators. All the data above the critical temperature indicate that the axial U(1) violation is consistent with zero within statistical errors. The quark mass dependence suggests disappearance of the U(1) anomaly at a rate comparable to that of the SU(2)_L x SU(2)_R symmetry breaking.