Flavor-Parity Breaking in the NJL Model with Wilson Fermions

TL;DR

This paper investigates how adding a Wilson term to the NJL model causes explicit parity-flavor symmetry breaking, leading to a phase with spontaneous symmetry breaking confirmed through numerical simulations.

Contribution

It provides numerical evidence for the parity-flavor breaking phase in the NJL model with Wilson fermions, validating large N predictions and analyzing finite size effects.

Findings

Existence of a parity-flavor breaking phase confirmed numerically.

Large finite size effects significantly alter the phase boundary.

Massless pions appear at the phase boundary.

Abstract

The Nambu--Jona-Lasinio model is chirally symmetric. Addition of a Wilson term explicitly breaks this symmetry and leaves the model with a remaining parity-flavor symmetry. In the approximation of a large number of colors it has been shown that there is a phase where the remaining parity-flavor symmetry is spontaneously broken and that on the phase boundary all pions become massless. Using numerical simulations we confirm the existence of this phase for the case of two flavors and two colors. We also confirm the large N prediction of the existence of large finite size effects that alter the shape of the phase boundary dramatically when periodic boundary conditions are used.