Probing sub-GeV Dark Matter-Baryon Scattering with Cosmological
  Observables
  We derive new limits on the elastic scattering cross-section between baryons
and dark matter using Cosmic Microwave Background data from the Planck
satellite and measurements of the Lyman-alpha forest flux power spectrum from
the Sloan Digital Sky Survey. Our analysis addresses generic cross sections of
the form $\sigma\propto v^n$, where v is the dark matter-baryon relative
velocity, allowing for constraints on the cross section independent of specific
particle physics models. We include high-$\ell$ polarization data from Planck
in our analysis, improving over previous constraints. We apply a more careful
treatment of dark matter thermal evolution than previously done, allowing us to
extend our constraints down to dark matter masses of $\sim$MeV. We show in this
work that cosmological probes are complementary to current direct detection and
astrophysical searches.
