Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 10, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1475-7516/2013/10/025
Keywords
dark matter theory; gamma ray theory; gamma ray experiments
Funding
- FNRS-FRS
- IISN
- FWO Vlaanderen [1271513]
- Strategic Research Program High Energy Physics of the Vrije Universiteit Brussel
- Belgian Federal Science Policy through the Interuniversity Attraction Pole [P7/37]
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There has been interest recently on particle physics models that may give rise to sharp gamma ray spectral features from dark matter annihilation. Because dark matter is supposed to be electrically neutral, it is challenging to build weakly interacting massive particle models that may accommodate both a large cross section into gamma rays at, say, the Galactic center, and the right dark matter abundance. In this work, we consider the gamma ray signatures of a class of scalar dark matter models that interact with Standard Model dominantly through heavy vector-like fermions (the vector-like portal). We focus on a real scalar singlet S annihilating into lepton-antilepton pairs. Because this two-body final-state annihilation channel is d-wave suppressed in the chiral limit, sigma(f (f) over bar)upsilon proportional to upsilon(4), we show that virtual internal bremsstrahlung emission of a gamma ray gives a large correction, both today and at the time of freeze-out. For the sake of comparison, we confront this scenario to the familiar case of a Majorana singlet annihilating into light lepton-antilepton pairs, and show that the virtual internal bremsstrahlung signal may be enhanced by a factor of (up to) two orders of magnitude. We discuss the scope and possible generalizations of the model.
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