Mass Generation without Phase Coherence at Nonzero Temperature

TL;DR

This paper investigates fermion mass generation in a 2+1d SU(2)xSU(2) Nambu-Jona-Lasinio model at various temperatures, revealing mass generation without chiral symmetry breaking and analyzing related lattice effects.

Contribution

It provides numerical evidence of fermion mass generation without phase coherence at nonzero temperature and compares results with large-N_f theoretical predictions.

Findings

Fermion mass generated without chiral symmetry breaking at T>0

Critical exponents match 1/N_f expansion predictions at T=0

No significant change in the speed of light in the hot phase

Abstract

We present results from numerical simulations of the 2+1d SU(2)xSU(2) Nambu - Jona-Lasinio model with N_f=4 fermion flavours at zero and nonzero temperature T. At zero temperature, critical exponents are extracted from the scaling of the order parameter and fermion mass and are found to be consistent with next-to-leading order predictions of the 1/N_f expansion. At nonzero temperature we observe fermion mass generation despite the lack of chiral symmetry breaking, which is forbidden by the Colemann-Mermin-Wagner theorem for all T>0. We study the effects of lattice discretisation and finite volume on the dynamically generated fermion mass. By study of the lattice dispersion relation we also show that in the hot phase there is no significant temperature induced modification to the speed of light. Studies of the equation of state are made by measuring the pressure as a function of temperature and comparison is made with large-N_f predictions.