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Dark Matter Induced Scalarization as a Possible Solution to the Hyperon Puzzle

Suchana Adhikari, Teruaki Suyama

Abstract

We investigate the properties of neutron stars when a massive scalar field, which could comprise all dark matter, is non-minimally coupled to the Ricci scalar. This coupling generates additional contributions to the field's effective mass, leading to tachyonic instabilities inside neutron stars and giving rise to rich phenomenology. Within this framework, we obtain neutron-star configurations with maximum masses exceeding 2 $M_\odot$, even when hyperons, which typically soften the equation of state and significantly lower the maximum mass, are included. Furthermore, we find that larger coupling strengths lead to multiple solutions for the scalar-field configuration. We analyze the structure of the corresponding effective potential responsible for this behavior. We also investigate how the inclusion of a scalar self-interaction term, in addition to the non-minimal coupling, modifies the resulting neutron-star properties.

Dark Matter Induced Scalarization as a Possible Solution to the Hyperon Puzzle

Abstract

We investigate the properties of neutron stars when a massive scalar field, which could comprise all dark matter, is non-minimally coupled to the Ricci scalar. This coupling generates additional contributions to the field's effective mass, leading to tachyonic instabilities inside neutron stars and giving rise to rich phenomenology. Within this framework, we obtain neutron-star configurations with maximum masses exceeding 2 , even when hyperons, which typically soften the equation of state and significantly lower the maximum mass, are included. Furthermore, we find that larger coupling strengths lead to multiple solutions for the scalar-field configuration. We analyze the structure of the corresponding effective potential responsible for this behavior. We also investigate how the inclusion of a scalar self-interaction term, in addition to the non-minimal coupling, modifies the resulting neutron-star properties.
Paper Structure (15 sections, 30 equations, 11 figures)

This paper contains 15 sections, 30 equations, 11 figures.

Table of Contents

  1. Introduction
  2. Basic equations
  3. Action of our model and covariant field equations
  4. The basic equations for the neutron star
  5. Qualitative behavior of the spontaneous scalarization
  6. Numerical methodology
  7. Results and Discussions
  8. The scalar field profile
  9. The dependence of Mass-Radius curve on xi and m
  10. Dependence of the Mass-Radius Curve on m
  11. Dependence of the Mass Radius Curve on xi
  12. Effects of self-interaction
  13. Consequence on the hyperon puzzle
  14. Conclusions
  15. Explicit expressions of A0, A1, B1, B2, C1, C2

Figures (11)

  • Figure 1: The effective potential in the absence of matter $\rho=0$ (blue curve) and in the presence of dense matter $\rho >\rho_{\rm th}$ (orange curve).
  • Figure 2: Plot explaining the trajectory of the scalar field particle. (i) The blue ball represents the particle that does not oscillate and is the most stable configuration. The green ball oscillates about the origin before reaching the surface. (ii) The motion of the particle after reaching the surface must reach 0.
  • Figure 3: Left panel: scalar field profile for a single non-trivial symmetric solution for $\xi=10$, $\lambda_\phi=6280 \text{ km}$, and $p_c=100\,\text{MeV/fm}^3$. Right panel: Effective gravitational constant $G_{\rm eff}$ corresponding to the scalar field profile given in the left panel.
  • Figure 4: Scalar field profiles for the two non-trivial symmetric solutions obtained for $\xi=20$,$\lambda_\phi=6280 \text{ km}$, and $p_c=300\,\text{ MeV/fm}^3$.
  • Figure 5: Ground and excited state scalar field profiles for the three non-trivial symmetric solutions obtained for $\xi=50$, $\lambda_\phi=6280 \text{ km}$, and $p_c=300\,\text{MeV/fm}^3$.
  • ...and 6 more figures