Effects of Phi and $σ^{*}$-meson on properties of hyperon stars including $Δ$ resonance

TL;DR

The paper addresses the hyperon and $\Delta$-resonance puzzles in neutron-star matter by deploying an extended IUFSU Relativistic Mean-Field model that includes hyperons, $\Delta$ resonances, and strange mesons $\sigma^{*}$ and $\phi$. It employs a $\sigma$-cut scheme to stiffen the EOS at high densities and explores a range of $x_{\sigma\Delta}$ couplings (1.05, 1.1, 1.15) with $x_{\omega\Delta}=1.1$ and $x_{\rho\Delta}=1$, computing EOSs, mass-radius relations via the Tolman-Oppenheimer-Volkoff equations, and tidal deformabilities through $k_2$ and $\Lambda$. Key results show strange mesons appear near $3\rho_0$ and modestly soften the high-density EOS, while $\Delta$ resonances soften the EOS at low density but can appear earlier as $x_{\sigma\Delta}$ increases, suppressing hyperons. The $\sigma$-cut scheme stiffens the high-density EOS enough to reach $M_{\max} \gtrsim 2M_{\odot}$ and yields smaller NS radii, with tidal deformabilities compatible with GW170817 bounds and NICER mass-radius measurements for appropriate parameter choices.

Abstract

In this work, we study the properties of neutron stars using the linear Relativistic Mean-Field (RMF) theory and consider multiple degrees of freedom inside neutron stars, including hyperons and $Δ$ resonances. We investigate different coupling parameters $x_{σΔ}$ between $Δ$ resonances and nucleons and compare the differences between neutron stars with and without strange mesons $σ^*$ and $φ$. These effects include particle number distributions, equations of state (EOS), mass-radius relations, and tidal deformabilities. To overcome the "hyperon puzzle," we employ the $σ-cut$ scheme to obtain neutron stars with masses up to $2M_{\odot}$. We find that strange mesons appear at around 3$ρ_0$ and reduce the critical density of baryons in the high-density region. With increasing coupling parameter $x_{σΔ}$, the $Δ$ resonances suppress hyperons, leading to a shift of the critical density towards lower values. The early appearance of $Δ$ resonances may play a crucial role in the stability of neutron stars. Strange mesons soften the EOS slightly, while $Δ$ resonances predominantly soften the EOS in the low-density region. By calculating tidal deformabilities and comparing with astronomical observation GW170817, we find that the inclusion of $Δ$ resonances decreases the radius of neutron stars.

Figures (9)

• Figure 1: Effective mass of nucleons versus baryon density in NS matter using and not using $\sigma$-cut scheme with considering $\sigma^*$ and $\phi$ or not.
• Figure 2: Field strength of various mesons with considering $\sigma^*$ and $\phi$ or not.
• Figure 3: Field strength of various mesons with considering $\sigma^*$ and $\phi$ or not, $c_{\sigma}$=0.15
• Figure 4: Relative population of particles versus baryon density without $\sigma$-cut scheme with considering $\sigma^*$ and $\phi$ or not, $x_{\sigma \Delta}$=1.05, $x_{\sigma \Delta}$=1.1, $x_{\sigma \Delta}$=1.15.
• Figure 5: Relative population of particles versus baryon density with considering $\sigma^*$ and $\phi$ or not, and $c_\sigma=0.15$, $x_{\sigma \Delta}$=1.05, $x_{\sigma \Delta}$=1.1, $x_{\sigma \Delta}$=1.15.