Roberge-Weiss transition in $N_f=2$ QCD with staggered fermions and $N_\tau=6$

TL;DR

This study investigates the Roberge-Weiss transition in two-flavor QCD with staggered fermions at $N_ au=6$, examining how lattice spacing and discretization affect the tricritical point and phase transition nature.

Contribution

It provides the first analysis of the Roberge-Weiss transition at $N_ au=6$ and compares effects of different fermion discretizations on the tricritical point in two-flavor QCD.

Findings

The tricritical pion mass shifts between $N_ au=4$ and $N_ au=6$.

Discretization affects the position of the tricritical point.

Finite size scaling reveals changes in transition order with lattice parameters.

Abstract

The QCD phase diagram at imaginary chemical potential exhibits a rich structure and studying it can constrain the phase diagram at real values of the chemical potential. Moreover, at imaginary chemical potential standard numerical techniques based on importance sampling can be applied, since no sign problem is present. In the last decade, a first understanding of the QCD phase diagram at purely imaginary chemical potential has been developed, but most of it is so far based on investigations on coarse lattices ($N_\tau=4$, $a=0.3\:$fm). Considering the $N_f=2$ case, at the Roberge-Weiss critical value of the imaginary chemical potential, the chiral/deconfinement transition is first order for light/heavy quark masses and second order for intermediate values of the mass: there are then two tricritical masses, whose position strongly depends on the lattice spacing and on the discretization. On $N_\tau=4$, we have the chiral $m_\pi^{\text{tric.}}=400\:$MeV with unimproved staggered fermions and $m_\pi^{\text{tric.}}\gtrsim900\:$MeV with unimproved pure Wilson fermions. Employing finite size scaling we investigate the change of this tricritical point between $N_\tau=4$ and $N_\tau=6$ as well as between Wilson and staggered discretizations.