Effects of quark-matter symmetry energy on hadron-quark coexistence in neutron-star matter

TL;DR

This paper investigates how isovector-vector and hypercharge-vector couplings in quark matter influence the hadron-quark phase transition and properties of neutron stars, revealing that these couplings affect the phase coexistence region and neutron star maximum mass.

Contribution

It introduces a detailed analysis of vector couplings in quark matter within neutron stars, highlighting their impact on phase transition and stellar properties, which was not thoroughly explored before.

Findings

Isovector-vector and hypercharge-vector couplings increase symmetry energy in neutron-star matter.

These couplings cause the hadron-quark mixed phase to shrink or shift to higher densities.

Maximum neutron-star mass slightly increases with the inclusion of these couplings.

Abstract

We examine the effects of the isovector-vector coupling and hypercharge-vector coupling in quark matter on hadron-quark coexistence in neutron-star matter. The relativistic mean field theory with the TM1 parameter set and an extended TM1 parameter set are used to describe hadronic matter, and the Nambu-Jona-Lasinio model with scalar, isoscalar-vector, isovector-vector and hypercharge-vector couplings is used to describe deconfined quark matter. The hadron-quark phase transition is constructed via the Gibbs conditions for phase equilibrium. The isovector-vector and hypercharge-vector couplings in quark matter enhance the symmetry energy and hypercharge symmetry energy in neutron-star matter, while their effects are found to be suppressed at high densities by the strange quarks. As a result, the hadron-quark mixed phase shrinks with only isovector-vector coupling and moves to higher density with isovector-vector and hypercharge-vector couplings. The maximum mass of neutron-star increases slightly with isovector-vector and hypercharge-vector couplings.