Proto-neutron Stars with Dark Matter Admixture: A Single-Fluid Approach

TL;DR

This paper investigates how a fermionic dark matter component, interacting with ordinary matter through a Higgs portal, influences proto-neutron star evolution within a single-fluid framework. By fixing the entropy per baryon and lepton fraction and varying the DM mass during the Kelvin-Helmholtz phase, the authors find that DM absorbs thermal energy, reduces the core temperature, alters neutrino emission, and softens the equation of state, leading to more compact stars. To satisfy the observed $2\,M_\odot$ neutron star constraint under the DDME2 EoS, they derive an upper DM mass bound of $m_\Chi \leq 0.62$ GeV for PNS evolution, while cold neutron stars can sustain heavier DM masses due to higher central densities and stronger gravitational binding. The work highlights how DM–OM coupling and neutrino physics shape the thermal and structural evolution of compact stars and provides observationally relevant constraints that depend on the nuclear EoS and DM properties.

Abstract

This work investigates the impact of dark matter (DM) on the microscopic and macroscopic properties of proto-neutron stars (PNSs). We employ a single-fluid framework in which DM interacts with ordinary matter (OM) via the Higgs portal and remains in thermal equilibrium through non-gravitational interactions. Using a quasi-static approximation, we analyze the evolution of PNSs during the Kelvin-Helmholtz phase by varying the DM mass while keeping the entropy per baryon and lepton fraction fixed. Our results show that DM absorbs thermal energy from the stellar medium without efficient re-emission, thereby altering neutrino emission and affecting the star's thermal evolution history. Furthermore, neutrinos contribute significantly to pressure support in the PNS phase, inhibiting DM mass accretion during neutrino-trapped stages. Based on the requirement to satisfy the observed $2,\rm M_\odot$ neutron star mass constraint and to maintain consistency with supernova remnant data, we suggest an upper limit of $m_χ\leq 0.62,\rm GeV$ for the DM mass that can accrete in evolving PNSs, within the model framework. In contrast, we established that cold neutron stars (NSs) can support higher DM masses without compromising equilibrium stability, owing to increased central density, enhanced gravitational binding energy, and reduced thermal pressure.

Figures (9)

• Figure 1: The figure shows the particle fraction as a function of $n_B/n_0$. We show four snapshots comprising a neutrino-trapped regime (upper panels) and a neutrino-transparent regime (bottom panels). Stellar matter without a DM component is shown with solid lines across all four evolutionary stages. For fixed-entropy configurations, dashed lines correspond to stars admixed with DM of mass $m_\chi = 0.4\,\text{GeV}$, while dash-dot-dash lines indicate $m_\chi = 0.62\,\text{GeV}$. In the cold stars case, dash-double-dot lines represent stars admixed with 1 GeV DM, and dotted lines correspond to those mixed with 2 GeV DM mass. The brown vertical lines indicated in the figures represent the position of the central baryon density, $n_c$, of the corresponding stellar configuration, following the same line style.
• Figure 2: The particle fraction for a neutralino DM particle with mass 200 GeV admixed with NSs is shown. In this analysis, the DM mass is fixed, and the DM content is controlled by varying the DM Fermi momentum ($k_F^D$). Different line styles represent the values of $k_F^D$ considered: the solid line corresponds to $k_F^D = 0$, the dashed line to $k_F^D = 20\,\text{MeV}$, the dash-dot line to $k_F^D = 40\,\text{MeV}$, and the dotted line to $k_F^D = 60\,\text{MeV}$. For readers interested in the corresponding stellar structure associated with these DM configurations, further details can be found in Ref. Das:2021hnkLopes:2023uxiDas:2018frcLopes:2024ixlLourenco:2021dvh.
• Figure 3: This figure displays pressure as a function of energy density. Stellar matter without a DM component is shown with solid lines across all four evolutionary stages. For fixed-entropy configurations, dashed lines correspond to stars admixed with DM of mass $m_\chi = 0.4\,\text{GeV}$, while dash-dot-dash lines indicate $m_\chi = 0.62\,\text{GeV}$. In the cold stars case, dash-double-dot lines represent stars admixed with 1 GeV DM, and dotted lines correspond to those mixed with 2 GeV DM mass.
• Figure 4: Variation of the squared speed of sound, $c_s^2$, with $n_B/n_0$ for different DM mass parameterizations.
• Figure 5: The figure shows the temperature profiles within the stellar matter from a newly born star as it evolves through neutrino diffusion to the neutrino-transparent stage.