Mapping the evolution of supernova-neutrino-boosted dark matter within the Milky Way

TL;DR

This work analyzes the temporal and spatial signatures of Milky Way SNν BDM for sub-GeV DM, contrasting local MW flux with the diffuse background from all past SNe (DBDM). Using a Monte Carlo MW CCSN distribution over $10^5$ years and a detailed BDM flux formalism that accounts for boost kinematics, neutrino spectra, and Earth geometry, the authors map the time evolution and sky distribution of SNν BDM across different $m_χ/T_χ$ regimes. They find that nonrelativistic SNν BDM behaves as a diffuse background, while ultrarelativistic BDM yields transient, localized signals; however, the DBDM component generally dominates diffuse flux except in narrow angular windows. Analyses with MW SNRs support the main conclusion, reinforcing DBDM as the primary target for SNν BDM searches until the next galactic SN offers new detection opportunities, with implications for sub-GeV DM phenomenology and experimental strategies.

Abstract

Supernova-neutrino-boosted dark matter (SN$ν$ BDM) has emerged as a promising portal for probing sub-GeV dark matter. In this work, we investigate the behavior of BDM signatures originating from core-collapse supernovae within the Milky Way (MW) over the past one hundred thousand years, examining both their temporal evolution and present-day spatial distributions. We show that while the MW BDM signature is approximately diffuse in the nonrelativistic regime, it exhibits significant temporal variation and spatial localization when the BDM is relativistic. Importantly, we compare these local MW signatures with the previously proposed diffuse SN$ν$ BDM (DBDM), which arises from the accumulated flux of all past supernovae in the Universe [Y.-H. Lin and M.-R. Wu, Phys. Rev. Lett. 133, 111004 (2024)]. In the nonrelativistic limit, DBDM consistently dominates over the local diffuse MW BDM signature. Only when the MW BDM becomes ultrarelativistic and transitions into a transient, highly-localized signal can it potentially surpass the DBDM background. This work thus reinforces the importance of DBDM for SN$ν$ BDM searches until the next galactic SN offers new opportunities.

Figures (15)

• Figure 1: Schematic plot for the coordinate system used to generate the mock SN dataset in this work. The GC is located at the origin of the cylindrical coordinate system, where $(R,z,\phi)$ correspond to the radial distance, vertical height, and azimuthal angle, respectively. The coordinates $(R_\star,z_\star,\phi_\star)$ indicate the position of a SN.
• Figure 2: Locations of SNe (blue dots) over the past 100,000 years across the MW projected on the $x$-$y$ plane. The Earth, shown as a green circle, is located at $(x, y, z) = (-R_e, 0, 0)$ in Cartesian coordinates. The gray dashed line encloses the $3\sigma$ range of SN occurrence probability. A total of 1,667 SNe are included in this dataset.
• Figure 3: Schematic plot showing the geometry and coordinates used to compute the SN$\nu$ BDM. SN ($\mathsf{S}$), GC ($\mathsf{G}$), and Earth ($\mathsf{E}$) lie on the same plane. Halo DM is upscattered by SN$\nu$ at location $\mathsf{B}$ on the outward-propagating SN$\nu$ shell.
• Figure 4: Spatial distribution of SNe that contribute (orange circles) and do not contribute (blue circles) to the present-day BDM flux at Earth. $T_\chi = 0.5$ keV and 5 keV for the left and right panels. DM mass is taken to be $m_\chi=5$ keV for both panels. $\eta$ denotes the fraction of SNe contributing nonzero BDM flux from the whole dateset.
• Figure 5: $t_{\rm van}$ versus $m_\chi$/$T_\chi$ evaluated at $R_s=\bar{R}_s \approx 9.6$ kpc (red). Also shown are the approximated solutions of $t_{\rm van}$ from Eq. \ref{['eq:t_van_approx']} in the nonrelativistic (blue dotted line) and relativistic limits (orange dotted line). Two horizontal solid lines corresponding to 10,000 yrs (blue) and $\tau_{\rm CCNS}$ (green) are shown for reference.