Thermodynamics of the O(4) linear and nonlinear models within the auxiliary field method

TL;DR

This paper investigates the thermodynamics of O(4) linear and nonlinear models using the auxiliary field method, revealing how phase transition types depend on parameters and symmetry conditions.

Contribution

It introduces a unified approach to study both linear and nonlinear O(4) models at finite temperature through the auxiliary field method.

Findings

Transition from crossover to first order with increasing sigma mass

First order phase transition observed in the chiral limit

Goldstone's theorem is satisfied in the chiral limit

Abstract

The study of the O(N) model at nonzero temperature is presented applying the auxiliary field method, which allows to obtain a continuous transformation between the linear and the nonlinear version of the model. In case of explicitly broken chiral symmetry the order of the chiral phase transition changes from crossover to first order as the vacuum mass of the $\sigma$ particle increases. In the chiral limit one observes a first order phase transition and the Goldstone's theorem is fulfilled.