Selection Rule for Enhanced Dark Matter Annihilation

TL;DR

This paper introduces a selection rule based on exchange symmetry that can enhance or suppress dark matter annihilation channels, leading to potentially observable signals in the present Universe.

Contribution

It reveals a new selection mechanism affecting dark matter annihilation rates, especially highlighting the dominance of p-wave annihilation due to Sommerfeld enhancement.

Findings

p-wave annihilation can dominate current dark matter signals

The selection rule is linked to exchange symmetry of identical particles

Velocity-dependent annihilation rates are predicted

Abstract

We point out a selection rule for enhancement (suppression) of odd (even) partial waves of dark matter coannihilation or annihilation using Sommerfeld effect. Using this, the usually velocity-suppressed p-wave annihilation can dominate the annihilation signals in the present Universe. The selection mechanism is a manifestation of the exchange symmetry of identical incoming particles, and generic for multi-state DM with off-diagonal long-range interactions. As a consequence, the relic and late-time annihilation rates are parametrically different and a distinctive phenomenology, with large but strongly velocity-dependent annihilation rates, is predicted.