  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.
