|DATE||June 27 (Thu), 2019|
|TITLE||Reannihilation of self-interacting dark matter|
The phenomenology of a second epoch of efficient dark matter annihilation into dark radiation long after the standard thermal freeze-out is explored. Such a hidden reannihilation process could affect visible sectors only gravitationally. As a concrete realization, self-interacting dark matter (SIDM) is considered with a light (MeV-scale) force mediator coupled to dark radiation. It is demonstrated how quantum mechanical effects lead to strongly enhanced annihilation cross sections, which induce the reannihilation epoch. The effect is a temporally local modification of the Hubble expansion rate, and we show that the cosmic microwave background (CMB) measurements?as well as other observations?have a high sensitivity to observe this phenomenon. Special attention is given to the model region where late kinetic decoupling and strong self-interactions can alleviate several small-scale problems in the cold dark matter paradigm at the same time. Interestingly, we find that reannihilation might here also simultaneously lower the tension between CMB and low-redshift astronomical observations of the Hubble expansion rate.