Sensitivity of the Polyakov loop and related observables to chiral symmetry restoration

TL;DR

This study demonstrates that the Polyakov loop and related observables are sensitive to the chiral phase transition in QCD, exhibiting energy-like behavior near the critical temperature, with divergences in quark mass derivatives in the chiral limit.

Contribution

First lattice QCD evidence showing Polyakov loop behavior as an energy-like observable near the chiral transition, consistent with 3D O(2) universality class scaling.

Findings

Polyakov loop behaves as an energy-like observable near T_c

Quark mass derivatives diverge at T_c in the chiral limit

Temperature derivatives develop a spike at T_c

Abstract

While the Polyakov loop is an order parameter of the deconfinement transition in the heavy quark mass regime of QCD, its sensitivity to the deconfinement of light, dynamical quarks in QCD is not apparent. On the other hand, the quark mass dependence of the Polyakov loop is sensitive to the appearance of a chiral phase transition. Using lattice QCD calculations in the staggered fermion discretization scheme at finite values of the lattice spacing, $aT = 1/8$, we show here, for the first time, that the Polyakov loop expectation value, and the heavy quark free energy extracted from it, behave like energy-like observables in the vicinity of the chiral phase transition temperature $T_c$. Consistent with scaling behavior of energy-like observables in the 3-$d$, O(2) universality class, the quark mass derivatives diverge in the chiral limit at $T_c$ while the temperature derivatives stay finite. The latter will develop a characteristic spike at $T_c$. This, however, may be resolved only in calculations with quark masses being two orders of magnitude smaller than those currently accessible in lattice QCD calculations.