Condensation of lighter-than-physical pions in QCD

TL;DR

This paper investigates the phase diagram of QCD with lighter-than-physical pions at nonzero isospin chemical potential, revealing that the pion condensation transition line remains vertical and approaches the zero chemical potential axis as pion mass decreases.

Contribution

It provides new insights into how the pion condensation phase boundary behaves in the chiral limit with lighter-than-physical pions in QCD.

Findings

The BEC transition line remains vertical for lighter pions.

The transition line approaches the zero chemical potential axis linearly as pion mass decreases.

Results predict the phase diagram behavior in the chiral limit.

Abstract

We report on the results of the 2+1 flavour QCD simulations at nonzero isospin chemical potential performed at half the physical light quark mass. At low temperatures and large isospin chemical potential Bose-Einstein Condensation (BEC) occurs, creating a pion condensed phase, separated from the hadronic and quark-gluon plasma phases by the BEC transition line. For physical quark masses, the section of this line between the hadronic and BEC phases was found to be almost perfectly vertical, i.e. aligned with the temperature axis. We show that for lighter than physical pions, this section remains vertical, and approaches the axis of vanishing chemical potential linearly with the pion mass, giving a prediction of the phase diagram in the chiral limit.