Constraints on Dark Matter Microphysics from the Milky Way Satellite Population

22 Apr 2019  ·  Ethan O. Nadler, Vera Gluscevic, Kimberly K. Boddy, Risa H. Wechsler ·

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 derive conservative 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 matter power spectrum. We confirm and improve these results through a detailed probabilistic inference of the MW satellite population that marginalizes over relevant astrophysical uncertainties, yielding $95\%$ confidence upper limits on the scattering cross section of $6\times10^{-30}\ \rm{cm}^2$ ($10^{-27}\ \rm{cm}^2$) for DM particle masses of $10\ \rm{keV}$ ($10\ \rm{GeV}$). These limits improve upon cosmological bounds derived from cosmic-microwave-background anisotropy measurements by more than three 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.

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Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology