Phases of Hadron-Quark Matter in (Proto) Neutron Stars

TL;DR

This paper explores the existence and characteristics of hadron-quark mixed phases in neutron star cores, modeling their structure and composition using advanced theoretical frameworks, and finds that such phases occur only in very massive, slowly rotating neutron stars.

Contribution

It introduces detailed modeling of the hadron-quark pasta phase and its dependence on neutron star mass and rotation, using relativistic mean-field and Nambu-Jona-Lasinio models.

Findings

Hadron-quark pasta phase exists only in very massive neutron stars.

The phase is limited to stars with rotational frequencies less than 300 Hz.

The 't Hooft term significantly affects particle composition in proto-neutron stars.

Abstract

In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare phase geometries. Particular emphasis is given to modeling the size othis phase in rotating neutron stars. We use the relativistic mean-field theory to model hadronic matter and the non-local three-flavor Nambu-Jona-Lasinio model to describe quark matter. Based on these models, the hadron-quark pasta phase exists only in very massive neutron stars, whose rotational frequencies are less than around 300 Hz. All other stars are not dense enough to trigger quark deconfinement in their cores. Part two of the paper deals with the quark-hadron composition of hot (proto) neutron star matter. To this end we use a local three-flavor Polyakov-Nambu-Jona-Lasinio model which includes the 't Hooft (quark flavor mixing) term. It is found that this term leads to non-negligible changes in the particle composition of (proto) neutron stars made of hadron-quark matter.