Semi-annihilation is a generic feature of dark matter, when it is stabilised by a symmetry larger than a Z2. It results in a greater range of indirect detection signals, expands the parameter space that produces the observed relic density, and is frequently associated with multi-component dark sectors. We discuss several recent models that demonstrate the potential implications. First are two Higgs-portal models where semi-annihilation is essential to explaining the gamma ray excess observed by the Fermi telescope. Specifically, it allows us to avoid stringent direct detection constraints and, by changing the photon spectrum, also improves the quality of the fit. Next we consider the first example of a model with both semi-annihilation and the Sommerfeld enhancement. The interplay of these two features leads to a variety of signals; we discuss both current limits and future discovery prospects. Finally, we discuss some ongoing efforts to perform a systematic study of semi-annihilating models and the constraints that apply to them.

IBS Center for Theoretical Physics of the Universe