Neutron star properties in density-dependent relativistic Hartree-Fock theory

TL;DR

This study uses the density-dependent relativistic Hartree-Fock theory to analyze neutron star properties, predicting large proton fractions and maximum masses consistent with observations, and highlighting the impact of Fock terms on nuclear matter at high densities.

Contribution

First application of DDRHF theory to neutron star properties without hyperons, comparing results with RMF models and observational data.

Findings

DDRHF predicts large proton fractions affecting star cooling.

Maximum neutron star masses between 2.45 and 2.49 solar masses.

Mass-radius relations align with various observational constraints.

Abstract

With the equations of state provided by the newly developed density dependent relativistic Hartree-Fock (DDRHF) theory for hadronic matter, the properties of the static and $\beta$-equilibrium neutron stars without hyperons are studied for the first time, and compared to the predictions of the relativistic mean field (RMF) models and recent observational data. The influences of Fock terms on properties of asymmetric nuclear matter at high densities are discussed in details. Because of the significant contributions from the $\sigma$- and $\omega$-exchange terms to the symmetry energy, large proton fractions in neutron stars are predicted by the DDRHF calculations, which strongly affect the cooling process of the star. The critical mass about 1.45 $M_\odot$, close to the limit 1.5 $M_\odot$ determined by the modern soft X-ray data analysis, is obtained by DDRHF with the effective interactions PKO2 and PKO3 for the occurrence of direct Urca process in neutron stars. The maximum masses of neutron stars given by the DDRHF calculations lie between 2.45 M$_\odot$ and 2.49 M$_\odot$, which are in reasonable agreement with high pulsar mass $2.08 \pm 0.19 M_\odot$ from PSR B1516+02B. It is also found that the mass-radius relations of neutron stars determined by DDRHF are consistent with the observational data from thermal radiation measurement in the isolated neutron star RX J1856, QPOs frequency limits in LMXBs 4U 0614+09 and 4U 1636-536, and redshift determined in LMXBs EXO 0748-676.