The topological structures in strongly coupled QGP with chiral fermions on the lattice

TL;DR

This study investigates the topological structures and U(1) symmetry violation in strongly coupled quark-gluon plasma using lattice QCD techniques with chiral fermions, revealing persistent U(1) breaking near the chiral crossover.

Contribution

It provides the first lattice-based analysis of U(1) symmetry restoration and topological structures in QCD at finite temperature with chiral fermions.

Findings

U(1) symmetry is not effectively restored in the chiral crossover region

Topological susceptibility shows significant temperature dependence

Microscopic topological structures influence the strongly interacting QGP phase

Abstract

The nature of chiral phase transition for two flavor QCD is an interesting but unresolved problem. One of the most intriguing issues is whether or not the anomalous U(1) symmetry in the flavor sector is effectively restored along with the chiral symmetry. This may determine the universality class of the chiral phase transition. Since the physics near the chiral phase transition is essentially non-perturbative, we employ first principles lattice techniques to address this issue. We use overlap fermions, which have exact chiral symmetry on the lattice, to probe the anomalous U(1) symmetry violation of 2+1 flavor dynamical QCD configurations with domain wall fermions. The latter also optimally preserves chiral and flavor symmetries on the lattice, since it is known that the remnant chiral symmetry of the light quarks influences the scaling of the chiral condensate in the crossover transition region. We observe that the anomalous U(1) is not effectively restored in the chiral crossover region. We perform a systematic study of the finite size and cut-off effects since the signals of U(1) violation are sensitive to it. We also provide a glimpse of the microscopic topological structures of the QCD medium that are responsible for the strongly interacting nature of the quark gluon plasma phase. We study the effect of these microscopic constituents through our first calculations for the topological susceptibility of QCD at finite temperature, which could be a crucial input for the equation of state for anomalous hydrodynamics.