Direct Detection of Dark Matter Debris Flows

TL;DR

This paper investigates the properties of dark matter debris flows resulting from tidal stripping in the Milky Way, highlighting their significance for direct detection experiments due to their high velocity and distinctive signatures.

Contribution

It provides the first detailed analysis of dark matter debris flows in the Via Lactea II simulation, emphasizing their impact on direct detection signals and velocity distributions.

Findings

Debris flow constitutes over 50% of local dark matter at high velocities.

Debris flows produce distinctive recoil energy spectra.

Debris flows are spatially uniform at 8 kpc, ensuring their presence in detection experiments.

Abstract

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended "debris flows" in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.