Dark matter-radiation interactions: the impact on dark matter haloes

International audienceInteractions between dark matter (DM) and radiation (photons or neutrinos) inthe early Universe suppress density fluctuations on small mass scales. Here weperform a thorough analysis of structure formation in the fully non-linearregime using N-body simulations for models with DM-radiation interactions andcompare the results to a traditional calculation in which DM only interactsgravitationally. Significant differences arise due to the presence ofinteractions, in terms of the number of low-mass DM haloes and theirproperties, such as their spin and density profile. These differences areclearly seen even for haloes more massive than the scale on which densityfluctuations are suppressed. We also show that semi-analytical descriptions ofthe matter distribution in the non-linear regime fail to reproduce ournumerical results, emphasizing the challenge of predicting structure formationin models with physics beyond collisionless DM