High Energy Physics Seminar

Self-interacting dark matter (DM) has been put forward as a way to address potential problems with the Cold DM paradigm on sub-galactic scales. For a broad class of models the interactions between DM particles are mediated by a light force carrier. At temperatures above its mass, the force carrier effectively behaves as a dark radiation (DR) component that tightly couples to the DM, forming an almost perfect fluid. We expect this combined DM-DR system to give rise to sound waves propagating throughout the cosmos until DM kinematically decouples from the DR. Much like the standard baryon acoustic oscillations, these dark acoustic oscillations (DAO) imprint a characteristic scale, the sound horizon of dark matter, in the matter density field. We review how the microphysics of the DM-DR interaction affects the clustering of matter in the Universe and show that the DAO physics also gives rise to unique signatures in the temperature and polarization spectra of the cosmic microwave background (CMB). We use cosmological data from the CMB, baryon acoustic oscillations, and large-scale structure to constrain the possible fraction of interacting DM as well as the strength of its interaction with DR. We find that linear cosmological data and CMB lensing put strong constraints on existence of DAO features in the CMB and the large-scale structure of the Universe. We also show that our results are surprisingly constraining for the recently proposed Double-disk DM model, a novel example of how large-scale precision cosmological data can be used to constrain galactic physics and sub-galactic structure.