S8 Tension in the Context of Dark Matter–Baryon Scattering

Abstract

We explore an interacting dark matter (IDM) model that allows for a fraction of dark matter (DM) to undergo velocity-independent scattering with baryons. In this scenario, structure on small scales is suppressed relative to the cold DM scenario. Using the effective field theory of large-scale structure, we perform the first systematic analysis of BOSS full-shape galaxy clustering data for the IDM scenario, and we find that this model ameliorates the S 8 tension between large-scale structure and Planck data. Adding the S 8 prior from the Dark Energy Survey (DES) to our analysis further leads to a mild ∼3σ preference for a nonvanishing DM–baryon scattering cross section, assuming ∼10% of DM is interacting and has a particle mass of 1 MeV. This result produces a modest ∼20% suppression of the linear power at k ≲ 1 h Mpc−1, consistent with other small-scale structure observations. Similar scale-dependent power suppression was previously shown to have the potential to resolve S 8 tension between cosmological data sets. The validity of the specific IDM model explored here will be critically tested with upcoming galaxy surveys at the interaction level needed to alleviate the S 8 tension.