Two-flavor QCD at finite quark or isospin density

TL;DR

This paper uses analytic continuation to study the phase transitions of two-flavor QCD at finite quark or isospin density, revealing deviations from quadratic behavior and the potential for a first-order transition.

Contribution

It extends the analysis of QCD phase transitions to real chemical potentials using analytic continuation from imaginary values, comparing quark and isospin cases.

Findings

Deviations from quadratic dependence of pseudocritical lines on chemical potential.

Imaginary isospin chemical potential can strengthen the transition, potentially making it first order.

Quantified differences between quark and isospin chemical potential effects.

Abstract

We exploit analytic continuation to prolongate to the region of real chemical potentials the (pseudo)critical lines of QCD with two degenerate staggered fermions at nonzero temperature and quark or isospin density obtained in the region of imaginary chemical potentials. We determine the curvatures at zero chemical potential and quantify the deviation between the cases of finite quark and of finite isospin chemical potential. In both circumstances deviations from a quadratic dependence of the pseudocritical lines on the chemical potential are clearly seen. We try different extrapolations and, for the nonzero isospin chemical potential, confront them with the results of direct Monte Carlo simulations. We also find that, as for the finite quark chemical potential, an imaginary isospin chemical potential can strengthen the transition till turning it into strong first order.