Effects of short-range correlations at high densities on neutron stars with and without DM content: role of the repulsive self-interaction

TL;DR

This work demonstrates that short-range correlations (SRC) qualitatively alter the high-density behavior of relativistic hadronic equations of state (EoS) and, consequently, neutron-star structure. The authors formulate a relativistic mean-field model including SRC through a high-momentum tail in the nucleon distribution and analyze two vector self-interaction schemes: one with only quadratic terms ($\omega_0^2$) and another including a quartic term ($\omega_0^4$). They find that SRC soften the EoS when $C=0$ but can stiffen it when $C\neq0$, with corresponding impacts on the maximum NS mass $M_{\max}$ and mass–radius relations; in DM-admixed stars, SRC in the hadronic sector partially mitigate DM-induced softening, particularly for the $\omega_0^4$ case. All parametrizations remain compatible with current astrophysical constraints from NICER–XMM-Newton and GW190425, highlighting the role of hadronic SRC and higher-order vector interactions in dense matter physics and DM scenarios within NSs.

Abstract

In this work, we investigate how short-range correlations affect relativistic hadronic models at high densities, with direct consequences for the structure of neutron stars, both with and without dark matter content. Two versions of the model are examined: one with vector self-interactions up to second order ($ω_0^2$) and another including a fourth-order term ($ω_0^4$). We show that SRC tend to soften the equation of state when only the quadratic term is present, but produce a noticeable stiffening once the $ω_0^4$ term is included. The corresponding Tolman-Oppenheimer-Volkoff solutions for pure neutron stars indicate that short-range correlations reduce the maximum mass in the first case but increase it in the second. Extending the analysis to stars containing a fermionic dark matter component, within the two-fluid formalism, we verify that the same features appear in the respective mass-radius diagrams. In particular, the decrease of the maximum mass with increasing dark matter fraction is partly compensated by the SRC effects in the hadronic sector for the model with the fourth-order term. In all cases, the resulting parametrizations are consistent with recent astrophysical constraints, including the joint NICER-XMM-Newton analyses of the pulsars PSR J0030+0451 and PSR J0740+6620, as well as the gravitational-wave event GW190425.

Figures (10)

• Figure 1: SRC-induced enhancement factors $A_{\text{SRC},i}$ for neutrons and protons as functions of the proton fraction $y$, illustrating the impact of short-range correlations on high-momentum tails.
• Figure 2: Coefficient of the high-density pressure expansion as a function of proton fraction $y$, comparing RMF models with and without SRC for the NL3* parametrization.
• Figure 3: Variation of the high-density pressure expansion coefficient with proton fraction $y$, shown for different nuclear empirical parameters: $\rho_{\text{sat}}$, $E_{\text{sat}}$, $E_{\text{sym},2}$, and $m^*_{\text{sat}}$.
• Figure 4: High-density pressure expansion coefficient $B_{\text{SRC}}(y)$ from Eq. \ref{['eq:pressaprox2']}, plotted against proton fraction $y$ for $C = 0.01$ and varying nuclear empirical parameters.
• Figure 5: Pressure–energy density relations for RMF models with and without SRC in the stellar matter regime. Panel (a): models with $C = 0$; panel (b): models with $C \ne 0$.