Full-shape BOSS constraints on dark matter interacting with dark radiation and lifting the S8 tension

Abstract

Abstract In this work we derive constraints on interacting dark matter-dark radiation models from a full-shape analysis of BOSS-DR12 galaxy clustering data, combined with Planck legacy cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements. We consider a set of models parameterized within the effective theory of structure formation (ETHOS), quantifying the lifting of the S8 tension in view of KiDS weak-lensing results. The most favorable scenarios point to a fraction f ∼ 10-100% of interacting dark matter as well as a dark radiation temperature that is smaller by a factor ξ ∼ 0.1-0.15 compared to the CMB, leading to a reduction of the tension to the ∼ 1σ level. The temperature dependence of the interaction rate favored by relaxing the S8 tension is realized for a weakly coupled unbroken non-Abelian SU(N) gauge interaction in the dark sector. To map our results onto this SU(N) model, we compute higher-order corrections due to Debye screening. We find a lower bound αd ≡ gd 2/(4π) ≳ 10-8 (10-9) for dark matter mass 1000 (1) GeV for relaxing the S8 tension, consistent with upper bounds from galaxy ellipticities and compatible with self-interactions relevant for small-scale structure formation.