The finite temperature transition for 2-flavour lattice QCD at finite isospin density

TL;DR

This study investigates the finite temperature phase transition in 2-flavour lattice QCD at finite isospin density, revealing how the transition temperature varies with isospin chemical potential and identifying the nature of phase transitions.

Contribution

It provides new insights into the phase structure of lattice QCD at finite isospin density, including the behavior of the transition and the existence of a critical endpoint.

Findings

Transition temperature decreases with increasing isospin chemical potential.

Transitions are crossovers for mu_I < m_pi, with no critical endpoint observed.

Evidence of a critical endpoint for mu_I > m_pi indicating a change in phase transition order.

Abstract

We simulate 2-flavour lattice QCD at finite isospin chemical potential mu_I, for temperatures close to the finite temperature transition from hadronic matter to a quark-gluon plasma. The mu_I dependence of the transition coupling is observed and used to estimate the decrease in the transition temperature with increasing mu_I. These simulations are performed on an 8^3 times 4 lattice at 3 different quark masses. Our estimate of the magnitude of the fluctuations of the phase of the fermion determinant at small quark-number chemical potential mu, suggest that the position of the small mu and small mu_I transitions should be the same for mu_I=2mu, and we argue that the nature of these transitions should be the same. For all mu_I < m_pi the smoothness of these transitions and the values of the Binder cumulant B_4, indicate that these transitions are mere crossovers, and show no sign of the expected critical endpoint. For mu_I > m_pi and a small isospin (I_3) breaking term lambda, we do find evidence of a critical endpoint which would indicate that, for lambda=0, there is a tricritical point on the phase boundary where the pion condensate evaporates, where this phase transition changes from second to first order.