Roberge-Weiss endpoint at the physical point of $N_f = 2+1$ QCD

TL;DR

This study investigates the Roberge-Weiss critical point in $N_f=2+1$ QCD, determining its temperature and universality class through lattice simulations and finite size scaling analysis.

Contribution

It provides the first continuum extrapolation of the Roberge-Weiss endpoint temperature and confirms its universality class as 3D Ising in $N_f=2+1$ QCD.

Findings

The endpoint temperature is $T_{RW} = 208(5)$ MeV.

The ratio $T_{RW}/T_c$ is approximately 1.34.

Finite size scaling indicates a 3D Ising universality class.

Abstract

We study the phase diagram of $N_f = 2+1$ QCD in the $T - \mu_B$ plane and investigate the critical point corresponding to the onset of the Roberge-Weiss transition, which is found for imaginary values of $\mu_B$. We make use of stout improved staggered fermions and of the tree level Symanzik gauge action, and explore four different sets of lattice spacings, corresponding to $N_t = 4,6,8,10$, and different spatial sizes, in order to assess the universality class of the critical point. The continuum extrapolated value of the endpoint temperature is found to be $T_{\rm RW} = 208(5)$ MeV, i.e. $T_{\rm RW}/T_c \sim 1.34(7)$, where $T_c$ is the chiral pseudocritical temperature at zero chemical potential, while our finite size scaling analysis, performed on $N_t = 4$ and $N_t = 6$ lattices, provides evidence for a critical point in the $3d$ Ising universality class.