Order of the Roberge-Weiss endpoint (finite size transition) in 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.