Enhanced n-body annihilation of dark matter and its indirect signatures

Understand

We examine the possible indirect signatures of dark matter annihilation processes with a non-standard scaling with the dark matter density, and in particular the case where more than two dark matter particles participate in the annihilation process.

• We point out that such processes can be strongly enhanced at low velocities without violating unitarity, similar to Sommerfeld enhancement in the standard case of two-body annihilation, potentially leading to visible signals in indirect searches.
• We study in detail the impact of such multi-body annihilations on the ionization history of the universe and consequently the cosmic microwave background, and find that unlike in the two-body case, the dominant signal can naturally arise from the end of the cosmic dark ages, after the onset of structure formation.
• We examine the complementary constraints from the Galactic Center, Galactic halo, and galaxy clusters, and outline the circumstances under which each search would give rise to the strongest constraints.