Halo-to-Halo Similarity and Scatter in the Velocity Distribution of Dark Matter

TL;DR

This paper studies the velocity distribution of dark matter in halos across different scales, proposing an empirical model with implications for dark matter detection and highlighting key sources of scatter and uncertainty.

Contribution

It introduces a new empirical model for the dark matter velocity distribution function and analyzes the main sources of scatter affecting direct detection efforts.

Findings

The empirical VDF model has a wider peak and steeper tail than Maxwell-Boltzmann.

Uncertainty in the solar system's position within the Milky Way halo is the dominant source of VDF scatter.

Physical explanations for the VDF shape are discussed.

Abstract

We examine the Velocity Distribution Function (VDF) in dark matter halos from Milky Way to cluster mass scales. We identify an empirical model for the VDF with a wider peak and a steeper tail than a Maxwell--Boltzmann distribution, and discuss physical explanations. We quantify sources of scatter in the VDF of cosmological halos and their implication for direct detection of dark matter. Given modern simulations and observations, we find that the most significant uncertainty in the VDF of the Milky Way arises from the unknown radial position of the solar system relative to the dark matter halo scale radius.