The nature of the Roberge-Weiss transition in $N_f=2$ QCD with Wilson fermions

Understand

At imaginary values of the quark chemical potential $\mu$, Quantum Chromodynamics shows an interesting phase structure due to an exact center, or Roberge-Weiss (RW), symmetry.

• This can be used to constrain QCD at real $\mu$, where the sign problem prevents Monte Carlo simulations of the lattice theory.
• In previous studies of this region with staggered fermions it was found that the RW endpoint, where the center transition changes from first-order to a crossover, depends non-trivially on the quark mass: for high and low masses, it is a triple point connecting to the deconfinement and chiral transitions, respectively, changing to a second-order endpoint for intermediate mass values.
• These parameter regions are separated by tricritical points.