Chiral thermodynamics of nuclear matter

TL;DR

This paper calculates the thermodynamic properties and phase diagram of isospin-asymmetric nuclear matter at finite temperature using in-medium chiral perturbation theory, including multi-pion exchanges and three-body forces, revealing the effects of isospin asymmetry.

Contribution

It provides a systematic chiral perturbation theory approach to nuclear matter thermodynamics, incorporating explicit two-pion exchange with Δ-isobar excitation and three-body forces, and explores the phase transition behavior.

Findings

Critical temperature for symmetric nuclear matter is 15.1 MeV.

Liquid-gas coexistence region diminishes with increasing isospin asymmetry.

Four-body correlations have small corrections to the free energy.

Abstract

The free energy and the equation of state of isospin-asymmetric nuclear matter are calculated at finite temperature up to three loop order in the framework of in-medium chiral perturbation theory, systematically incorporating one- and two-pion exchange dynamics to this order. Effects from the two-pion exchange with explicit {\Delta}-isobar excitation are included, as well as three-body forces. We construct the phase diagram of nuclear matter for different proton fractions x_p and investigate the dependence of nuclear matter properties on the isospin-asymmetry. A detailed study of the liquid-gas phase transition is performed. For isospin-symmetric nuclear matter we find a critical temperature of 15.1 MeV; as the isospin-asymmetry is increased, the liquid-gas coexistence region decreases until it disappears at x_p \approx 0.05, while nuclear matter becomes unbound at x_p \approx 0.12. The quadratic expansion of the free energy in the asymmetry parameter {\delta} is a good approximation at low temperature even for large {\delta}. An estimate of chiral four-body correlations in nuclear and neutron matter is also performed and the corrections from such four-body interactions are found to be small.