Impact of substructure on local dark matter searches

Abstract

Dark matter substructure can contribute significantly to local dark matter searches and may provide a large uncertainty in the interpretation of those experiments. For direct detection experiments, sub-halos give rise to an additional dark matter component on top of the smooth dark matter distribution of the host halo. In the case of dark matter capture in the Sun, sub-halo encounters temporarily increase the number of captured particles. Even if the encounter happened in the past, the number of dark matter particles captured by the Sun can still be enhanced today compared to expectations from the host halo as those enhancements decay over time. Using results from an analytical model of the sub-halo population of a Milky Way-like galaxy, valid for sub-halo masses between $10^{-5}\,M_\odot$ and $10^{11}\,M_\odot$, we assess the impact of sub-halos on direct dark matter searches in a probabilistic way. We find that the impact on direct detection can be sizable, with a probability of $\sim 10^{-3}$ to find an $\mathcal{O}(1)$ enhancement of the recoil rate. In the case of the capture rate in the Sun, we find that $\mathcal{O}(1)$ enhancements are very unlikely, with probability $\lesssim 10^{-5}$, and are even impossible for some dark matter masses.