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

Supernova-neutrino-boosted dark matter (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>SN</a:mi><a:mi>ν</a:mi></a:math> 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 <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>SN</c:mi><c:mi>ν</c:mi></c:math> BDM (DBDM), which arises from the accumulated flux of all past supernovae in the Universe [Y.-H. Lin and M.-R. Wu, ]. 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 <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>SN</e:mi><e:mi>ν</e:mi></e:math> BDM searches until the next galactic SN offers new opportunities.