Antiproton constraints on dark matter annihilations from internal electroweak bremsstrahlung

Abstract

If the dark matter particle is a Majorana fermion, annihilations into two\nfermions and one gauge boson could have, for some choices of the parameters of\nthe model, a non-negligible cross-section. Using a toy model of leptophilic\ndark matter, we calculate the constraints on the annihilation cross-section\ninto two electrons and one weak gauge boson from the PAMELA measurements of the\ncosmic antiproton-to-proton flux ratio. Furthermore, we calculate the maximal\nastrophysical boost factor allowed in the Milky Way under the assumption that\nthe leptophilic dark matter particle is the dominant component of dark matter\nin our Universe. These constraints constitute very conservative estimates on\nthe boost factor for more realistic models where the dark matter particle also\ncouples to quarks and weak gauge bosons, such as the lightest neutralino which\nwe also analyze for some concrete benchmark points. The limits on the\nastrophysical boost factors presented here could be used to evaluate the\nprospects to detect a gamma-ray signal from dark matter annihilations at\ncurrently operating IACTs as well as in the projected CTA.\n