# Anapole dark matter annihilation into photons

## TL;DR

This paper investigates the annihilation processes of anapole dark matter, revealing that it can annihilate into photons via s-wave and p-wave channels, with astrophysical constraints limiting the s-wave contribution.

## Contribution

It provides the first explicit calculation of both tree-level and diphoton annihilation channels for anapole dark matter, highlighting the significance of s-wave processes.

## Key findings

- S-wave annihilation can be comparable to p-wave depending on parameters.
- Astrophysical bounds exclude models with large s-wave annihilation.
- Explicit cross section calculations for anapole DM annihilation channels.

## Abstract

In models of anapole dark matter (DM), the DM candidate is a Majorana fermion whose primary interaction with standard model (SM) particles is through an anapole coupling to off-shell photons. As such, at tree-level, anapole DM undergoes p-wave annihilation into SM charged fermions via a virtual photon. But, generally, Majorana fermions are polarizable, coupling to two real photons. This fact admits the possibility that anapole DM can annihilate into two photons in an s-wave process. Using an explicit model, we compute both the tree-level and diphoton contributions to the anapole DM annihilation cross section. Depending on model parameters, the s-wave process can either rival or be dwarfed by the p-wave contribution to the total annihilation cross section. Subjecting the model to astrophysical upper bounds on the s-wave annihilation mode, we rule out the model with large s-wave annihilation.