From asymmetric nuclear matter to neutron stars: a functional renormalization group study

TL;DR

This study extends a chiral nucleon-meson model to isospin-asymmetric matter, using the functional renormalization group to analyze phase transitions, equations of state, and chiral symmetry restoration relevant for neutron stars.

Contribution

It introduces a FRG-based approach to asymmetric nuclear matter, providing improved insights into phase transitions and neutron star matter properties.

Findings

Equations of state agree with realistic many-body calculations.

Chiral symmetry remains broken in neutron matter with fluctuations.

Model satisfies constraints from two-solar-mass neutron stars.

Abstract

A previous study of nuclear matter in a chiral nucleon-meson model is extended to isospin-asymmetric matter. Fluctuations beyond mean-field approximation are treated in the framework of the functional renormalization group. The nuclear liquid-gas phase transition is investigated in detail as a function of the proton fraction in asymmetric matter. The equations of state at zero temperature of both symmetric nuclear matter and pure neutron matter are found to be in good agreement with realistic many-body computations. We also study the density dependence of the pion mass in the medium. The question of chiral symmetry restoration in neutron matter is addressed; we find a stabilization of the phase with spontaneously broken chiral symmetry once fluctuations are included. Finally, neutron star matter including beta equilibrium is discussed. The model satisfies the constraints imposed by the existence of two-solar-mass neutron stars.