Dark matter hurricane: Measuring the S1 stream with dark matter detectors

Abstract

The recently discovered S1 stream passes through the Solar neighbourhood on a low inclination, counter-rotating orbit. The progenitor of S1 is a dwarf galaxy with a total mass comparable to the present-day Fornax dwarf spheroidal, so the stream is expected to have a significant DM component. We compute the effects of the S1 stream on WIMP and axion detectors as a function of the density of its unmeasured dark component. In WIMP detectors the S1 stream supplies more high energy nuclear recoils so will marginally improve DM detection prospects. We find that even if S1 comprises less than 10% of the local density, multi-ton xenon WIMP detectors can distinguish the S1 stream from the bulk halo in the relatively narrow mass range between 5 and 25 GeV. In directional WIMP detectors such as CYGNUS, S1 increases DM detection prospects more substantially since it enhances the anisotropy of the WIMP signal. Finally, we show that axion haloscopes possess by far the greatest potential sensitivity to the S1 stream if its dark matter component is sufficiently cold. Once the axion mass has been discovered, the distinctive velocity distribution of S1 can easily be extracted from the axion power spectrum.

Velocity substructure from Gaia and direct searches for dark matter

“…As most of the changes in the recoil spectrum are brought about by S1, the phenomenology of the Dark Shards as a departure from the SHM will be very similar to the case studied in Ref. [74]. Following what was concluded then, we concur that the impact of the Dark Shards will be minor for nuclear recoil based experiments unless S1 and the Retrograde shards are particularly prominent in the DM of the ex situ halo.…”

“…The effect from S1 was considered in detail in Ref. [74], including also the dependence on the S1 velocity dispersion.…”

“…For masses of this size scattering with xenon, the spectrum should in fact be the most sensitive to changes to f (v) (see Ref. [74] for a quantitative discussion). However despite this choice, and even increasing the maximum value of ξ tot to 20% to make the changes more noticeable, they remain small.…”

“…Modelling suggests that their progenitors had virial masses ≈ 10 10 M and stellar masses ≈ 10 6 M , comparable to modern day dwarf spheroidal satellites like Draco and Ursa Minor. As the S1 stream is counterrotating, its associated DM meets the Earth head-on, so it leaves characteristic signatures in experiments sensitive to high DM speeds [74]. The S2 stellar stream is on a polar orbit that passes through the Earth.…”

Implications of the Gaia sausage for dark matter nuclear interactions

“…Another promising avenue to look for interesting signatures of DM substructure are axion searches and directional detection experiments as discussed in refs. [37][38][39]. The main drawback of the aforementioned analyses is the underlying assumption of a near perfect stellar-DM velocity correlation.…”