Wednesday, January 11, 2017
In supersymmetry, the lightest supersymmetric particles (LSP) are well-motivated candidates for dark matter. When the Peccei-Quinn (PQ) symmetry is evoked to solve the strong CP problem, the axion becomes another viable candidate. The axion's scalar superpartner, the saxion, however significantly changes the conventional picture. During inflation, a potential for saxions is induced and displaces the saxion field value away from the vev today. This results in a large saxion condensate that dominates the energy density of the Universe. The saxion subsequently decays to the particles in the thermal bath, generating a large amount of entropy and diluting the dark matter abundance. We focus on the cases where dark matter is the axion from the misalignment mechanism, or the axino/gravitino LSP that arises from the thermal scattering and Freeze-In processes. The former case allows the PQ and grand unification scales to be comparable, whereas the latter case allows a high reheat temperature after inflation, solving the axino/graviton problems. We will also discuss interesting phenomenology for this class of theories, e.g. dark radiation and displaced vertices at colliders.