# Constraints on Dark Matter Microphysics from the Milky Way Satellite Population

## TL;DR

This paper uses the observed Milky Way satellite galaxies to set new, stringent limits on the collisional properties of dark matter, especially DM-baryon interactions, surpassing previous cosmological bounds across a wide mass range.

## Contribution

It provides the first detailed probabilistic inference of DM-baryon scattering constraints from satellite data, improving existing bounds by orders of magnitude and exploring implications for alternative dark matter models.

## Key findings

- 95% confidence upper limits on scattering cross section at 2×10^{-29} cm^2 for 10 keV DM
- Constraints extend to DM masses up to 10 GeV, surpassing cosmological bounds
- Results impact warm and fuzzy dark matter scenarios

## Abstract

Alternatives to the cold, collisionless dark matter (DM) paradigm in which DM behaves as a collisional fluid generically suppress small-scale structure. Herein we use the observed population of Milky Way (MW) satellite galaxies to constrain the collisional nature of DM, focusing on DM-baryon scattering. We first derive analytic upper limits on the velocity-independent DM-baryon scattering cross section by translating the upper bound on the lowest mass of halos inferred to host satellites into a characteristic cutoff scale in the linear matter power spectrum. We then confirm and improve these results through a detailed probabilistic inference of the MW satellite population that marginalizes over relevant astrophysical uncertainties. This yields $95\%$ confidence upper limits on the DM-baryon scattering cross section of $2\times10^{-29}\ \rm{cm}^2$ ($6\times 10^{-27}\ \rm{cm}^2$) for DM particle masses $m_\chi$ of~$10\ \rm{keV}$ ($10\ \rm{GeV}$); these limits scale as $m_\chi^{1/4}$ for $m_\chi \ll 1\ \rm{GeV}$ and $m_\chi$ for~$m_\chi \gg 1\ \rm{GeV}$. This analysis improves upon cosmological bounds derived from cosmic-microwave-background anisotropy measurements by multiple orders of magnitude over a wide range of DM masses, excluding regions of parameter space previously unexplored by other methods, including direct-detection experiments. Our work reveals a mapping between DM-baryon scattering and other alternative DM models, and we discuss the implications of our results for warm and fuzzy DM scenarios.