# Enhancing Dark Matter Annihilation Rates with Dark Bremsstrahlung

## TL;DR

Including dark initial state radiation can lift suppression in dark matter annihilation, creating dominant s-wave channels that impact detection strategies, with this process proceeding at the same order as simpler two-body annihilation.

## Contribution

Demonstrates that dark initial state radiation opens unsuppressed s-wave annihilation channels, providing a new dominant process in certain dark matter interactions.

## Key findings

- Dark bremsstrahlung can dominate dark matter annihilation.
- This process proceeds at the same order in the new physics scale as 2-body annihilation.
- Implications for LHC and indirect detection searches.

## Abstract

Many dark matter interaction types lead to annihilation processes which suffer from p-wave suppression or helicity suppression, rendering them subdominant to unsuppressed s-wave processes. We demonstrate that the natural inclusion of dark initial state radiation can open an unsuppressed s-wave annihilation channel, and thus provide the dominant dark matter annihilation process for particular interaction types. We illustrate this effect with the bremsstrahlung of a dark spin-0 or dark spin-1 particle from fermionic dark matter, $\overline{\chi}\chi\rightarrow \overline{f}f\phi$ or $\overline{f}fZ'$. The dark initial state radiation process, despite having a 3-body final state, proceeds at the same order in the new physics scale $\Lambda$ as the annihilation to the 2-body final state $\overline{\chi}\chi\rightarrow \overline{f}f$. This is lower order in $\Lambda$ than the well-studied lifting of helicity suppression via Standard Model final state radiation, or virtual internal bremsstrahlung. This dark bremsstrahlung process should influence LHC and indirect detection searches for dark matter.