Dark Matter Direct Detection with Non-Maxwellian Velocity Structure

TL;DR

This paper investigates how non-Maxwellian velocity distributions of dark matter, derived from high-resolution simulations, significantly impact direct detection signals, especially for inelastic and light dark matter models, altering expected rates and modulation features.

Contribution

It provides the first detailed analysis of non-Maxwellian velocity effects on dark matter detection signals using high-resolution simulations, revealing substantial impacts on experimental interpretations.

Findings

Directional detection signals are more contrasted and directionally shifted.

Annual modulation signals can be enhanced or altered significantly.

Signal spectra show features due to substructure, affecting experimental compatibility.

Abstract

The velocity distribution function of dark matter particles is expected to show significant departures from a Maxwell-Boltzmann distribution. This can have profound effects on the predicted dark matter - nucleon scattering rates in direct detection experiments, especially for dark matter models in which the scattering is sensitive to the high velocity tail of the distribution, such as inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for experiments that require high energy recoil events, such as many directionally sensitive experiments. Here we determine the velocity distribution functions from two of the highest resolution numerical simulations of Galactic dark matter structure (Via Lactea II and GHALO), and study the effects for these scenarios. For directional detection, we find that the observed departures from Maxwell-Boltzmann increase the contrast of the signal and change the typical direction of incoming DM particles. For iDM, the expected signals at direct detection experiments are changed dramatically: the annual modulation can be enhanced by more than a factor two, and the relative rates of DAMA compared to CDMS can change by an order of magnitude, while those compared to CRESST can change by a factor of two. The spectrum of the signal can also change dramatically, with many features arising due to substructure. For LDM the spectral effects are smaller, but changes do arise that improve the compatibility with existing experiments. We find that the phase of the modulation can depend upon energy, which would help discriminate against background should it be found.