QCD phase structure at finite isospin chemical potential and smaller-than-physical quark mass

TL;DR

This paper investigates the phase structure of QCD at finite isospin chemical potential with smaller-than-physical quark masses, using lattice simulations to explore pion condensation and its dependence on quark mass and temperature.

Contribution

The study provides lattice QCD results at smaller quark masses supporting the scenario of pion condensation at arbitrary nonzero isospin chemical potential in the chiral limit.

Findings

Pion condensation boundary remains vertical at physical quark masses.

Lattice results support pion condensation at any nonzero isospin chemical potential in the chiral limit.

Results suggest the phase structure persists at smaller-than-physical quark masses.

Abstract

Introduction of a nonzero isospin chemical potential in QCD leads to the emergence of a pion condensed phase at sufficiently large $\mu_I$, bounded by a second order transition line. At zero temperature the pion condensate appears at $\mu_I = m_\pi / 2$. Recent numerical studies at physical quark masses show that the pion condensation boundary remains vertical up to the meeting point with the chiral crossover line. If this result remains valid when the light quark mass (and the pion mass) goes to zero, then in the chiral limit at temperatures below the chiral transition pion condensation happens at arbitrary nonzero $\mu_I$. We report on results of a lattice QCD simulation of a 2+1 flavour QCD at nonzero isospin chemical potential, at smaller-than-physical light quark mass, that support this scenario.