Cosmological Histories of a Dark Sector Model

Abstract:  The Dark matter problem has been around for almost a century. Its canonical solution is to add a new elementary particle to the Standard Model and investigate its cosmological consequences. Arguably, the most well-motivated possibility, and the one that has driven much of the theoretical and experimental work in the field, is that of a Weakly Interacting Massive Particle (WIMP). Yet, the absence of a WIMP signal pushes one to investigate more complicated scenarios that retain the attractive features of a WIMP. In this work, we consider a dark sector model; where dark matter couples to the ordinary particles indirectly through a singlet mediator. If this mediator is a heavy neutral lepton, it could provide a solution to the neutrino mass problem. Adding a third state to complete the model, the cosmological creation mechanisms  of dark matter and the internal dynamics of the dark sector are studied. We recover the WIMP behavior in the large coupling limit, and find that the three dark particles can establish thermal equilibrium when the mediator interacts strongly with dark matter, but weakly with ordinary particles.