Equation of state of imbalanced cold matter from chiral perturbation theory

TL;DR

This paper derives the equation of state for imbalanced cold matter using chiral perturbation theory, providing analytical expressions that match lattice QCD results and exploring phase crossover behaviors.

Contribution

It offers a simple analytical formula for the equation of state in pion and kaon condensed phases derived from leading order chiral perturbation theory, validated against lattice data.

Findings

Analytical expression for the energy density ratio peak

Agreement with lattice QCD simulations

Identification of the breakdown point of chiral perturbation theory at high isospin chemical potential

Abstract

We study the thermodynamic properties of matter at vanishing temperature for non-extreme values of the isospin chemical potential and of the strange quark chemical potential. From the leading order pressure obtained by maximizing the static chiral Lagrangian density we derive a simple expression for the equation of state in the pion condensed phase and in the kaon condensed phase. We find an analytical expression for the maximum of the ratio between the energy density and the Stefan-Boltzmann energy density as well as for the isospin chemical potential at the peak both in good agreement with lattice simulations of quantum chromodynamics. We speculate on the location of the crossover from the Bose-Einstein condensate state to the Bardeen-Cooper-Schrieffer state by a simple analysis of the thermodynamic properties of the system. For $\mu_I \gtrsim 2 m_\pi$ the leading order chiral perturbation theory breaks down; as an example it underestimates the energy density of the system and leads to a wrong asymptotic behavior.