Critical Density and Impact of $\Delta (1232)$ Resonance Formation in Neutron Stars

TL;DR

This study explores how the formation of elta(1232) resonances affects neutron star properties, revealing dependencies on symmetry energy, in-medium mass, and coupling constants, with implications for neutron star composition and structure.

Contribution

It introduces the first detailed analysis of how microphysical properties like symmetry energy and elta parameters influence elta formation and neutron star characteristics within an extended RMF model.

Findings

Critical elta densities depend on symmetry energy components.

The first elta^- appears at approximately 2.08 times nuclear saturation density.

Neutron star mass-radius relations are sensitive to elta parameters.

Abstract

The critical densities and impact of forming \D resonances in neutron stars are investigated within an extended nonlinear relativistic mean-field (RMF) model. The critical densities for the formation of four different charge states of \D are found to depend differently on the separate kinetic and potential parts of nuclear symmetry energy, the first example of a microphysical property of neutron stars to do so. Moreover, they are sensitive to the in-medium Delta mass $m_{\Delta}$ and the completely unknown $\Delta$-$\rho$ coupling strength $g_{\rho\Delta}$. In the universal baryon-meson coupling scheme where the respective $\Delta$-meson and nucleon-meson coupling constants are assumed to be the same, the critical density for the first $\Delta^-(1232)$ to appear is found to be \rc=$(2.08\pm0.02)\rho_0$ using RMF model parameters consistent with current constraints on all seven macroscopic parameters usually used to characterize the equation of state (EoS) of isospin-asymmetric nuclear matter (ANM) at saturation density $\rho_0$. Moreover, the composition and the mass-radius relation of neutron stars are found to depend significantly on the values of the $g_{\rho\Delta}$ and $m_{\Delta}$.