The order of the Roberge-Weiss endpoint (finite size transition) in QCD

TL;DR

This paper investigates the nature of the Roberge-Weiss endpoint in QCD, revealing its order varies with quark mass and suggesting a possible universality class, with implications for understanding the QCD phase diagram.

Contribution

It provides a detailed analysis of the Roberge-Weiss endpoint's order in two-flavor QCD and explores its dependence on quark mass, connecting it to large N_c QCD and universality classes.

Findings

The RW endpoint is first order at very large and small quark masses.

It weakens at intermediate masses, likely belonging to the 3D Ising universality class.

The study links the RW endpoint to finite size transitions in large N_c QCD.

Abstract

We consider the endpoint of the Roberge-Weiss (RW) first order transition line present for imaginary baryon chemical potentials. We remark that it coincides with the finite size transition relevant in the context of large $N_c$ QCD and study its order in the theory with two degenerate flavors. The RW endpoint is first order in the limit of large and small quark masses, while it weakens for intermediate masses where it is likely in the Ising 3d universality class. Phenomenological implications and further speculations about the QCD phase diagram are discussed.