Abstract
Data from the Gaia satellite show that the solar neighbourhood of the Milky
Way's stellar halo is imprinted with substructure from several accretion
events. Evidence of these events is found in "the Shards", stars clustering
with high significance in both action space and metallicity. Stars in the
Shards share a common origin, likely as ancient satellite galaxies of the Milky
Way, so will be embedded in dark matter (DM) counterparts. These "Dark Shards"
contain two substantial streams (S1 and S2), as well as several retrograde,
prograde and lower energy objects. The retrograde stream S1 has a very high
Earth-frame speed of $550$ km/s while S2 moves on a prograde, but highly
polar orbit and enhances peak of the speed distribution at around $300$ km/s.
The presence of the Dark Shards locally leads to modifications of many to the
fundamental properties of experimental DM signals. The S2 stream in particular
gives rise to an array of effects in searches for axions and in the time
dependence of nuclear recoils: shifting the peak day, inducing non-sinusoidal
distortions, and increasing the importance of the gravitational focusing of DM
by the Sun. Dark Shards additionally bring new features for directional
signals, while also enhancing the DM flux towards Cygnus.
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