Low-Temperature Enhancement of Semi-annihilation and the AMS-02 Positron Anomaly

Understand

Semi-annihilation is a generic feature of particle dark matter that is most easily probed by cosmic ray experiments.

• We explore models where the semi-annihilation cross section is enhanced at late times and low temperatures by the presence of an s-channel resonance near threshold.
• The relic density is then sensitive to the evolution of the dark matter temperature, and we compute expressions for the associated Boltzmann equation valid in general semi-annihilating models.
• At late times, a self-heating effect warms the dark matter, allowing number-changing processes to remain effective long after kinetic decoupling of the dark and visible sectors.