O(4) scaling analysis in two-flavor QCD at finite temperature and density with improved Wilson quarks

TL;DR

This study investigates the curvature of the chiral transition line in two-flavor QCD at finite temperature and density using improved Wilson quarks, confirming O(4) universality and finding a very small curvature parameter.

Contribution

The paper extends the O(4) scaling analysis to finite chemical potential in two-flavor QCD with improved Wilson quarks, providing a new estimate of the transition line curvature.

Findings

Confirmed O(4) universality at zero chemical potential

Extended scaling analysis to finite chemical potential

Found a small curvature parameter κ=0.0006(1) in the chiral limit

Abstract

We study the curvature of the chiral transition/crossover line between the low-temperature hadronic phase and the high-temperature quark-gluon-plasma phase at low densities, performing simulations of two-flavor QCD with improved Wilson quarks. After confirming that the chiral order parameter defined by a Ward-Takahashi identity is consistent with the scaling of the O(4) universality class at zero chemical potential, we extend the scaling analysis to finite chemical potential to determine the curvature of the chiral transition/crossover line at low densities assuming the O(4) universality. To convert the curvature in lattice units to that of the $T_c(\mu_B)$ in physical units, we evaluate the lattice scale applying a gradient flow method. We find $\kappa=0.0006(1)$ in the chiral limit, which is much smaller than that obtained in (2+1)-flavor QCD with improved staggered quarks.