Competition between delta isobars and hyperons and properties of compact stars

Jia Jie Li,Armen Sedrakian,Fridolin Weber

doi:10.1016/j.physletb.2018.06.051

Abstract

The Δ-isobar degrees of freedom are included in the covariant density functional (CDF) theory to study the equation of state (EoS) and composition of dense matter in compact stars. In addition to Δ's we include the full octet of baryons, which allows us to study the interplay between the onset of delta isobars and hyperonic degrees of freedom. Using both the Hartree and Hartree–Fock approximation we find that Δ's appear already at densities slightly above the saturation density of nuclear matter for a wide range of the meson–Δ coupling constants. This delays the appearance of hyperons and significantly affects the gross properties of compact stars. Specifically, Δ's soften the EoS at low densities but stiffen it at high densities. This softening reduces the radius of a canonical 1.4M⊙ star by up to 2 km for a reasonably attractive Δ potential in matter, while the stiffening results in larger maximum masses of compact stars. We conclude that the hypernuclear CDF parametrizations that satisfy the 2M⊙ maximum mass constraint remain valid when Δ isobars are included, with the important consequence that the resulting stellar radii are shifted toward lower values, which is in agreement with the analysis of neutron star radii.

Highlights

Compact stars are unique laboratories for studies of dense hadronic matter [1,2,3,4,5,6]
The current observational programs focusing on neutron stars combined with the nuclear physics modeling of their interiors are aimed at resolving the puzzles associated with their equation of state (EoS) and interior composition
We start with a brief outline of our theoretical framework, which is based on the covariant density functional (CDF) theory treated in the Hartree and Hartree-Fock approximations

Summary

Introduction

Compact stars are unique laboratories for studies of dense hadronic matter [1,2,3,4,5,6]. A number of studies of ∆’s in neutron star matter appeared which were conducted within the CDF theory in the Hartree approximation, i.e., the so-called relativistic meanfield model [28, 29, 34,35,36,37,38,39,40,41].

CDF model for stellar matter

Meson-baryon couplings

Summary and conclusions