Dark Matter Capture in a Core-Collapse Supernova Revives Dark Photons

TL;DR

This paper addresses how DM captured in a SN progenitor affects cooling bounds on dark photons with kinetic mixing $\epsilon$ and mass $m_{A'}$. The authors develop a self-consistent framework that treats DM capture (including light mediators) and distinguishes annihilating from asymmetric DM, then compute the modified dark-photon opacity and luminosity. They find that annihilating DM typically leaves SN1987A cooling bounds intact, while asymmetric DM can form a dark photosphere that suppresses dark-photon energy loss and reopens regions of the $(m_{A'}, \epsilon)$ parameter space, depending on DM mass and self-interactions. This work highlights the importance of incorporating astrophysical DM populations when deriving stellar-cooling constraints on dark sectors and points to future refinements with realistic SN simulations and plasma effects.

Abstract

Core-collapse supernovae serve as powerful probes of light, weakly coupled particles, such as dark photons. The conventional SN1987A cooling bound constrains the dark photon mass-mixing parameter space by requiring that the luminosity from the proto-neutron star core not exceed the observed neutrino emission. In this work, we revisit these limits by including the effect of dark matter (DM) captured inside the progenitor star before collapse. The trapped DM acts as an additional scattering target for dark photons, modifying their free-streaming length and, consequently, the supernova cooling rate. We perform a self-consistent analysis for both annihilating and asymmetric DM scenarios, incorporating light-mediator effects in the capture rate calculation. For annihilating DM, the equilibrium density remains too small to affect the bounds significantly. In contrast, asymmetric DM can accumulate to large densities, leading to the formation of a "dark photosphere" that suppresses the dark-photon luminosity and reopens previously excluded regions of parameter space. Our results emphasise the importance of accounting for astrophysical DM populations when deriving stellar-cooling constraints on dark sectors.

Figures (7)

• Figure 1: The standard SN1987A cooling bound forms an exclusion band in the $(m_{A'},\epsilon)$ plane. For very small kinetic mixing, dark photons are produced too weakly to alter the cooling. For very large mixing, frequent scatterings trap and thermalise the $A'$, suppressing energy loss. Only in the intermediate regime do $A'$ particles free-stream out and overcool the proto-neutron star, leading to the excluded region.
• Figure 2: Time evolution of the total number of annihilating DM captured inside the neutron star. The teal line denotes a benchmark where evolution is governed by Eq. (\ref{['eq:annDM1']}) and DM number grows by passing through a linear phase, followed by an exponential phase, before saturating to a plateau given by Eq. (\ref{['eq:dmann_sat_1']}). The red line denotes a benchmark where the system passes through subsequent phases of linear growth, with an interim period of exponential growth, before reaching saturation given by Eq. (\ref{['eq:eq2']}). Here we used $v_{\rm esc} \sim 1000\,\rm km\,s^{-1}$ and local dark matter density to be 0.4 GeV$\,\rm cm^{-3}$.
• Figure 3: Time evolution of the total number of non-annihilating DM captured inside the neutron star. The teal line denotes a benchmark where the system passes through subsequent phases of linear and exponential growth, as described by Eq. (\ref{['eq:assdm_1']}). The red line, on the other hand, denotes a benchmark where evolution is governed by Eq. (\ref{['eq:assdm_2']}) and DM number grows by passing through two subsequent linear phases. The number of DM particles at large times coincides for these two cases.
• Figure 4: Cartoon depicting how inclusion of DM changes the original cooling mechanism via $A^\prime$ emission in a typical neutron star.
• Figure 5: SN Cooling constraint for annihilating DM. The cross-section $\sigma_{\chi \chi} = 10^{-30}\,{\rm cm}^2$, and the coupling $\alpha'=0.03$. The constraint is similar in nature to the scenario with no captured dark matter. The upper boundary of the teal shaded portion denotes constraints from the surface emission, while the lower boundary is due to the exclusion from volume emission.