The chiral phase transition at non-zero imaginary baryon chemical potential for different numbers of quark flavours

TL;DR

This paper investigates how the first-order chiral transition region in QCD changes with lattice spacing and imaginary baryon chemical potential, suggesting a tricritical point where the transition becomes second order.

Contribution

It extends previous studies of the Columbia plot to include imaginary chemical potential, revealing consistent shrinking of the first-order region with finer lattices and tricritical scaling behavior.

Findings

First-order region shrinks with decreasing lattice spacing.

Scaling behavior suggests a tricritical point at zero chemical potential.

Results are consistent across different numbers of quark flavors.

Abstract

The so-called Columbia plot summarises the order of the QCD thermal transition as a function of the number of quark flavours and their masses. Recently, it was demonstrated that the first-order chiral transition region, as seen for $N_f \in [ 3,6 ]$ on coarse lattices, exhibits tricritical scaling while extrapolating to zero on sufficiently fine lattices. Here we extend these studies to imaginary baryon chemical potential. A similar shrinking of the first-order region is observed with decreasing lattice spacing, which again appears compatible with a tricritical extrapolation to zero.