Nucleon-quark mixed matter and neutron star EOS

TL;DR

This paper develops models of neutron star matter incorporating nucleon-quark interactions within the Brueckner-Hartree-Fock framework, showing how these interactions influence the star's mass-radius relationship and align with recent observations.

Contribution

It introduces two models of nucleon-quark mixed matter EoSs that account for quark effects and Pauli exclusion, advancing understanding of neutron star properties.

Findings

Nucleon-quark interactions significantly affect neutron star mass-radius curves.

Models predict maximum neutron star masses above 2.1 solar masses.

Inclusion of quark effects aligns theoretical EoSs with recent observational data.

Abstract

The nucleon-quark mixed matter is defined in the Brueckner-Hartree-Fock framework, in which quark densities are determined by equilibrium conditions between nucleon and quark chemical potentials, and nucleon-quark interactions play critical roles for resulting EoSs (equation of state). The two models of EoSs are derived from the nucleon-quark mixed matter (NQMM): The NQMM-A EoSs are based on the simple assumption that nucleons and free quarks occupy their respective Fermi levels and their Fermi spheres overlap from each other. In NQMM-B EoSs, the quark Fermi repulsion effect is incorporated on the basis of quakyonic matter, meaning that the nucleon Fermi levels are pushed up from the quark Fermi sphere by the Pauli exclusion principle. For the NQMM-A EoSs, the neutron-star mass-radius ($MR$) curves are pushed up above the region of $M \sim 2.1M_\odot$ and $R_{2.1M_\odot}\sim$ 12.5 km indicated by the recent observations, as the $qN$ repulsions increase. For the NQMM-B EoSs, the similar results are obtained by the combined contributions from the $qN$ repulsion and the quark Fermi repulsion. In both models of EoSs, the important roles of the $qN$ di-quark exchange repulsions are demonstrated to reproduce reasonable values of $M_{max}$ and $R_{2.1M_\odot}$.