Spontaneous Scalarization in Proto-neutron Stars

TL;DR

The paper investigates spontaneous scalarization in proto-neutron stars (PNSs) within scalar-tensor gravity using two coupling-function models and two finite-temperature EOS frameworks (the $SU(2)$ chiral sigma model and the Brueckner-Bethe-Goldstone-based EOS for hot, $\beta$-stable matter with/without neutrino trapping). By solving the Einstein-frame field equations for a spherically symmetric star and extracting the ADM mass and scalar charge, the authors show that finite temperature and EOS details significantly affect scalarization: PNSs generally exhibit lower maximum masses than cold NSs, and scalarization strength depends on $\beta$, entropy, and neutrino trapping, with Model 1 yielding larger deviations from GR than Model 2. The central scalar field and scalar charge exhibit sensitivity to the thermodynamic state, with neutrino trapping suppressing scalarization. Overall, the microphysical conditions inside PNSs can substantially modulate deviations from general relativity in scalar-tensor theories, highlighting the importance of realistic finite-temperature nuclear EOSs in gravitational tests with compact objects.

Abstract

Proto-neutron stars are born when a highly evolved and massive star collapses under gravity. In this paper, we investigate the spontaneous scalarization in proto-neutron stars. Based on the scalar tensor theory of gravity as well as the physical conditions in proto-neutron star, we examine the structure of proto-neutron star. To describe the fluid in proto-neutron star, we utilize $SU(2)$ chiral sigma model and the finite temperature extension of the Brueckner-Bethe-Goldstone quantum many-body theory in the Brueckner-Hartree-Fock approximation. Here, we apply the equation of state of proto-neutron stars considering different cases i.e. hot pure neutron matter and hot $β$-stable neutron star matter without neutrino trapping as well as with neutrino trapping. The effects of temperature and entropy of proto-neutron stars on the star structure are also studied. Our results confirm that the spontaneous scalarization is affected by different physical conditions in proto-neutron stars.

Figures (9)

• Figure 1: Pure neutron matter equation of state in the chiral sigma model at two temperatures sahu2004hot, $\rho_0=1.66\times10^{14}g/cm^3$.
• Figure 2: Left: Equation of state of $\beta$-stable neutron star matter at different values of the entropy per baryon $S/A$ in the case of neutrino-less pnseos2, Right: Same as Left but for the case of neutrino trapped matter (denoted by $\nu$) pnseos2, $\rho_0=1.66\times10^{14}g/cm^3$.
• Figure 3: PNS mass, $M,$ versus the central density, $\rho_c,$ for cold NS and PNS at finite temperature with different values of the coupling constant, $\beta$, in two models for the coupling function. The values in general relativity (GR) are also given.
• Figure 4: Same as Fig. \ref{['Mro']} but for PNSs with hot isoentropic $\beta$-stable neutron star matter without neutrino trapping and with neutrino trapping (denoted by $\nu$) for different values of entropy per baryon $S/A$.
• Figure 5: Mass versus the radius for cold NSs and PNSs with different equations of state and different values of the coupling constant in two models for the coupling function.