Chiral crossover vs chiral density wave in dense nuclear matter

TL;DR

This paper investigates the competition between isotropic and anisotropic chiral phases in dense nuclear matter, showing how a chiral density wave can disrupt the expected crossover transition and identifying conditions favoring its formation.

Contribution

It introduces a model that incorporates nucleonic and mesonic degrees of freedom to analyze the emergence of chiral density waves and their impact on phase transitions in dense matter.

Findings

Chiral phase transition is second order in the chiral limit, becomes a crossover with realistic pion mass.

Chiral density wave can be energetically favored, disrupting the smooth crossover.

Chiral density wave appears only at densities above about 6 times nuclear saturation density.

Abstract

We employ a model based on nucleonic and mesonic degrees of freedom to discuss the competition between isotropic and anisotropic phases in cold and dense matter. Assuming isotropy, the model exhibits a chiral phase transition which is of second order in the chiral limit and becomes a crossover in the case of a realistic pion mass. This observation crucially depends on the presence of the nucleonic vacuum contribution. Allowing for an anisotropic phase in the form of a chiral density wave can disrupt the smooth crossover. We identify the regions in the parameter space of the model where a chiral density wave is energetically preferred. A high-density re-appearance of the chiral density wave with unphysical behavior, as seen in previous studies, is avoided by a suitable renormalization scheme. A nonzero pion mass tends to disfavor the anisotropic phase compared to the chiral limit and we find that, within our model, the chiral density wave is only realized for baryon densities of at least about 6 times nuclear saturation density.