Exploring the impact of $\Delta$-isobars on Neutron Star

TL;DR

This study investigates how including $\Delta$-isobars in the neutron star equation of state affects star properties, demonstrating that their presence can significantly alter mass-radius relations and tidal deformability, aligning with observational constraints.

Contribution

It introduces the impact of $\Delta$-isobars on neutron star properties using RMF models and identifies parameter sets that satisfy observational constraints, highlighting their potential significance.

Findings

$\Delta$-isobars can appear at 2-3 times saturation density.

Adjusting coupling constants influences neutron star mass-radius profiles.

$\Delta$-isobars can lower the threshold density of $\Delta^-$-isobar below hyperons.

Abstract

We include the $\Delta$-isobars in the equation of state (EOS) of neutron star (NS) and study its effects with various parameter sets of the RMF model. We compare our results with the NS's constraints from the mass-radius measurement of PSR J0348+0432, PSR J1614-2230, PSR J0030+0451, PSR J0740+6620, PSR J0952-0607, and tidal deformability of GW170817. We calculate the mass-radius profile and tidal deformabilities of the NS using 21 parameter sets of the RMF model.Analyzing the result with various parameters, it is clear that only few parameter sets can satisfy simultaneously the constraints from NICER and GW170817. NLD parameter set satisfy all the constraints of NICER and GW170817. For its strong predictive power for the bulk properties of the neutron star, we take NLD parameter set as a representative for the detailed calculation of effect of $\Delta$-isobar on neutron star properties. We demonstrate that it is possible that $\Delta$-isobar can produce at 2-3 times the saturation density by adjusting the coupling constants $X_{\sigma\Delta}$, $X_{\rho\Delta}$ and $X_{\omega\Delta}$ in an appropriate range. Bulk properties of the NS like mass-radius profile and tidal deformability is strongly affected by the interaction strength of $\Delta$-isobar. Our calculation shows that it is also possible that by choosing $X_{\sigma\Delta}$, $X_{\rho\Delta}$ and $X_{\omega\Delta}$ to a suitable range the threshold density of $\Delta^-$-isobar become lower than $\Lambda^0$ hyperon. For a particular value of $\Delta$-coupling constants, the $R_{1.4}$ decrease by 1.7 km. This manuscipt give an argumentative justification for allowing $\Delta$-isobar degrees of freedom in the calculation of the NS properties.