Catching p via s wave with indirect detection

TL;DR

This paper explores how gauge boson radiation can lift helicity suppression in dark matter annihilation, enabling better experimental constraints from photon observations, especially for models involving neutrinos and photons.

Contribution

It introduces a method to constrain dark matter models with velocity-independent annihilation cross sections via photon signals, focusing on neutrino-photon final states.

Findings

Diffuse photon line searches provide the strongest constraints across mass ranges.

Photon measurements impose stronger bounds than neutrino observations for certain models.

Dark matter annihilation to neutrinos and photons is more constrained by photon data.

Abstract

For many dark matter models, the annihilation cross section to two-body final states is difficult to probe with current experiments because the dominant annihilation channel is velocity or helicity suppressed. The inclusion of gauge boson radiation for three-body final states can lift the helicity suppression, allowing a velocity-independent cross section to dominate the annihilation process, and providing an avenue to constrain these models. Here we examine experimental constraints on dark matter that annihilates to two leptons plus a bremsstrahlung boson, $\bar{\ell}+\ell+\gamma/W/Z$. We consider experimental constraints on photon final states from Fermi-LAT using both diffuse photon data and data from dwarf spheroidal galaxies, and compare to the implied constraints from 21 cm measurements. Diffuse photon line searches are generally the strongest over the entire mass regime. We in particular highlight the model in which dark matter annihilates to two neutrinos and a photon, and show that these models are more strongly constrained through photon measurements than through existing neutrino bounds.