The advent of the Gaia era has led to potentially revolutionary understanding of dark matter (DM) dynamics in our galaxy, which has important consequences for direct detection (DD) experiments. In this paper, we study how the empirical DM velocity distribution inferred from Gaia-Sausage, a dominant substructure in the solar neighborhood, affects the interpretation of DD data. We survey different classes of operators in the non-relativistic effective field theory that could arise from several relativistic benchmark models and emphasize that the Gaia velocity distribution could modify both the total number of events as well as the shape of the differential recoil spectra, the two primary observables in DD experiments. Employing the euclideanized signal method, we investigate the effects of the Gaia distribution on reconstructing DM model parameters and identifying the correct DM model given a positive signal at future DD experiments. We find that for light DM with mass ∼ 10 GeV, the Gaia distribution poses an additional challenge for characterizing DM interactions with ordinary matter, which may be addressed by combining complementary DD experiments with different targets and lowering the detection threshold. Meanwhile, for heavy DM with mass above ∼ 30 GeV, depending on the type of DM model, there could be a (moderate) improvement in the sensitivity at future DD experiments.

We study the mutual relationship between dark matter-electron scattering experiments and possible new dark matter substructure nearby hinted by the Gaia data. We show how kinematic substructure could affect the average and modulation spectra of dark matter-electron scattering in semiconductors and the discovery reaches of future experiments with these targets. Conversely, we demonstrate how future data could probe and constrain the fraction of dark matter in substructure, even when it constitutes a subdominant component of the local dark matter density.

We entertain the exotic possibility that dark matter (DM) decays or annihilations taking place in our galaxy may produce a flux of relativistic very weakly-coupled bosons, axions or dark photons. We show that there exist several upper bounds for this flux on Earth assuming generic minimal requirements for DM, such as a lifetime longer than the age of the Universe or an annihilation rate that leaves unaffected the background evolution during matter domination. These bounds do not depend on the identity or the couplings of the bosons. We then show that this new flux cannot be large enough to explain the recent XENON1T excess, while assuming that the bosons' couplings to the Standard Model are consistent with all current experimental and observational constraints. We also discuss a possible caveat to these bounds and a route to explain the excess.