W/Z bremsstrahlung as the dominant annihilation channel for dark matter

Dark matter annihilation to leptons, chi chi -> l (l) over bar, is necessarily accompanied by electroweak radiative corrections, in which a W or Z boson is radiated from a final-state particle. Given that the W and Z gauge bosons decay dominantly via hadronic channels, it is thus impossible to produce final-state leptons without accompanying protons, antiprotons, and gamma rays. Significantly, while many dark matter models feature a helicity-suppressed annihilation rate to fermions, radiating a massive gauge boson from a final-state fermion removes this helicity suppression, such that the branching ratios Br(lvW), Br(l(+)l(-)Z), and Br(v (v) over barZ) dominate over Br(l (l) over bar) W/Z bremsstrahlung thus allows indirect detection of many weakly interacting massive particle models that would otherwise be helicity suppressed, or v2 suppressed. Antiprotons and even antideuterons become consequential final-state particles. This is an important result for future dark matter searches. We discuss the implications of W/Z bremsstrahlung for `` leptonic'' dark matter models which aim to fit recent cosmic ray positron and antiproton data.