Limits on the Light Dark Matter–Proton Cross Section from Cosmic Large-Scale Structure
Keir K. Rogers, Cora Dvorkin, Hiranya V. Peiris
Abstract
We set the strongest limits to date on the velocity-independent dark matter (DM)--proton cross section $\ensuremath{\sigma}$ for DM masses $m=10\text{ }\text{ }\mathrm{keV}$ to 100 GeV, using large-scale structure traced by the Lyman-alpha forest: e.g., a 95% lower limit $\ensuremath{\sigma}<6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}\text{ }\text{ }{\mathrm{cm}}^{2}$, for $m=100\text{ }\text{ }\mathrm{keV}$. Our results complement direct detection, which has limited sensitivity to sub-GeV DM. We use an emulator of cosmological simulations, combined with data from the smallest cosmological scales used to date, to model and search for the imprint of primordial DM--proton collisions. Cosmological bounds are improved by up to a factor of 25.