Do Delta baryons play a role in neutron stars?

T.F Motta,A.W Thomas,P.A.M Guichon

doi:10.1016/j.physletb.2020.135266

Abstract

The presence of exotic hadrons, such as hyperons and Δ isobars, in the dense nuclear matter in their cores has been shown to produce important changes in the properties of neutron stars. Within the quark-meson coupling model, we show that the many-body forces generated by the change in the internal quark structure of the baryons in the strong scalar mean fields generated in dense nuclear matter prohibit the appearance of Δ isobars.

Highlights

The study of nuclear matter in β-equilibrium at densities above that of normal nuclear matter presents a number of outstanding challenges for modern nuclear theory
We have shown that the repulsive many-body forces that arise naturally in the quark-meson coupling (QMC) model from the quark substructure of the baryons increases the chemical potential of the ∆− in such a way that it cannot appear in a neutron star
For symmetric nuclear matter containing nucleons the internal response to the scalar mean field reduces the effective coupling to that field as the density rises, providing a novel saturation mechanism

Summary

Introduction

The study of nuclear matter in β-equilibrium at densities above that of normal nuclear matter presents a number of outstanding challenges for modern nuclear theory. It leads to the complete absence of Σ-hyperons in NS within the QMC model [7, 30] It is this OGE hyperfine interaction which splits the ∆ from the nucleon in free space in essentially all quark models and, as we have just explained, this mass difference will be enhanced in-medium. Already at twice nuclear matter density the mass splitting is enhanced by almost 100 MeV This already suggests that within the QMC model it is unlikely that the ∆ baryon will make an appearance. Our aim is to study the chemical potential of the ∆ in matter in β-equilibrium within the QMC model in order to understand whether it is likely to appear at any density relevant to the physics of neutron stars.

Equation of State for Dense Nuclear Matter

Equilibrium Conditions

Numerical results

Summary and Conclusions