Hypernuclear stars from relativistic Hartree-Fock density functional theory

TL;DR

This study explores hypernuclear matter using relativistic Hartree-Fock density functional theory, analyzing how hyperons affect the equation of state and the mass of neutron stars, with implications for astrophysical observations.

Contribution

It introduces a detailed relativistic Hartree-Fock approach with density-dependent couplings to model hypernuclear matter and compact stars, including tensor interactions and hyperonic couplings.

Findings

Fock terms soften the equation of state.

SU(6) model yields stars below 2 solar masses.

SU(3) model produces hypernuclear stars consistent with observations.

Abstract

The hypernuclear matter is studied within the relativistic Hartree-Fock theory employing several parametrizations of the hypernuclear density functional with density-dependent couplings. The equations of state and compositions of hypernuclear matter are determined for each parametrization and compact stars are constructed by solving their structure equations in spherical symmetry. We quantify the softening effect of Fock terms on the equation of state, as well as discuss the impact of tensor interactions, which are absent in the Hartree theories. Starting from models of density functionals which are fixed in the nuclear sector to the nuclear phenomenology, we vary the couplings in the hyperonic sector around the central values which are fitted to the hyperon potentials in nuclear matter. We use the SU(6) spin-flavor and SU(3) flavor symmetric quark models to relate the hyperonic couplings to the nucleonic ones. We find, consistent with previous Hartree studies, that for the SU(6) model the maximal masses of compact stars are below the two-solar mass limit. In the SU(3) model we find sufficiently massive compact stars with cores composed predominantly of $\Lambda$ and $\Xi$ hyperons and a low fraction of leptons (mostly electrons). The parameter space of the SU(3) model is identified where simultaneously hypernuclear compact stars obey the astrophysical limits on pulsar masses and the empirical hypernuclear potentials in nuclear matter are reproduced.