Semi-annihilation of Dark Matter

TL;DR

This paper explores semi-annihilation processes in dark matter, where particles interact to produce a different dark matter particle and an unstable state, affecting early universe dynamics and potential signals in indirect detection.

Contribution

It introduces the concept of semi-annihilation in dark matter models, highlighting its impact on relic abundance and indirect detection signals.

Findings

Semi-annihilation alters dark matter relic density calculations.

It provides new channels for indirect detection signals.

Semi-annihilation processes are allowed in models with larger stabilizing symmetries.

Abstract

The semi-annihilation reaction takes the schematic form psi_i psi_j -> psi_k phi, where psi_i are stable dark matter particles and phi is an unstable state. Such reactions are allowed when dark matter is stabilized by a larger symmetry than just Z_2. They lead to non-trivial dark matter dynamics in the early universe, and the thermal production of the relic particles can be completely controlled by semi-annihilations. This process might also take place today in the Milky Way, enriching the (semi-)annihilation final state spectrum observed in indirect detection experiments.