Dark Matter Halos as Particle Colliders: A Unified Solution to Small-Scale Structure Puzzles from Dwarfs to Clusters

TL;DR

This paper demonstrates that self-interacting dark matter (SIDM) can resolve small-scale structure issues across various cosmic scales by fitting halo data and measuring velocity-dependent cross sections, providing insights into dark matter particle physics.

Contribution

It introduces a unified approach to explain dark matter halo discrepancies using SIDM with velocity-dependent cross sections, constraining dark sector particle models.

Findings

SIDM with velocity-dependent cross section fits halo data across scales

Measured cross sections decrease from galaxy to cluster scales

Constraints on dark photon model parameters are significantly improved

Abstract

Astrophysical observations spanning dwarf galaxies to galaxy clusters indicate that dark matter (DM) halos are less dense in their central regions compared to expectations from collisionless DM N-body simulations. Using detailed fits to DM halos of galaxies and clusters, we show that self-interacting DM (SIDM) may provide a consistent solution to the DM deficit problem across all scales, even though individual systems exhibit a wide diversity in halo properties. Since the characteristic velocity of DM particles varies across these systems, we are able to measure the self-interaction cross section as a function of kinetic energy and thereby deduce the SIDM particle physics model parameters. Our results prefer a mildly velocity-dependent cross section, from $\sigma/m \simeq 2\; {\rm cm^2/g}$ on galaxy scales to $\sigma/m \simeq 0.1\; {\rm cm^2/g}$ on cluster scales, consistent with the upper limits from merging clusters. Our results dramatically improve the constraints on SIDM models and may allow the masses of both DM and dark mediator particles to be measured even if the dark sector is completely hidden from the Standard Model, which we illustrate for the dark photon model.