Theory for innovative cosmological tests of dark matter-baryon interactions

Among many things, dark matter could be made of new fundamental or composite particles, which may feebly interact with nuclei or electrons (“baryons”), as well as with themselves. Cosmological observables are a promising avenue to test such interactions, and are complementary to direct-detection experiments, in particular for probing relatively light dark matter particles. In this talk I will motivate two projects to build theoretical tools for innovative and higher-sensitivity cosmological tests of dark matter interactions -- in the hopes to recruit help in finishing them! In Project 1, I propose to expand and implement a new framework allowing us to study dark matter- baryon interactions and dark matter self-interactions simultaneously and self-consistently: the Boltzmann-Fokker-Planck (BFP) formalism, which I introduced in arXiv:1811.09903. The goal is to expand the BFP framework to incorporate dark matter self-interactions with arbitrary strengths, and implement it into the Boltzmann code CLASS. In Project 2, I motivate quantifying a completely novel signature of dark matter-baryon scattering, namely non-Gaussianity in the Cosmic Microwave Background (CMB) arising from the non-linearity of the dark matter-baryon momentum-exchange rate. This idea has similarities with a previous study my former student Jensen and I conducted on primordial black holes, which I will briefly highlight.