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High Energy Physics - Phenomenology

arXiv:1301.0021 (hep-ph)
[Submitted on 31 Dec 2012]

Title:On the likely dominance of WIMP annihilation to fermion pair+W/Z (and implication for indirect detection)

Authors:Thomas J. Weiler
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Abstract:Arguably, the most popular candidate for Dark Matter (DM) is a massive, stable, Majorana fermion. However, annihilation of Majorana DM to two fermions often features a helicity-suppressed s-wave rate. Radiating a gauge boson via electroweak (EW) and electromagnetic (EM) bremsstrahlung removes this s-wave suppression. The main purpose of this talk is to explain in some detail why the branching ratio to a fermion pair is likely suppressed while the decay to the pair plus a W/Z is not. In doing so, we investigate the general conditions for s-wave suppression and un-suppression using Fierz transformations and partial wave expansions. Suppression for the 2-to-2 process is sufficiently severe that the EW and EM bremsstrahlung are likely to be the dominant modes of gauge-singlet Majorana DM annihilation. We end this talk with a discussion of the challenge presented by space-based data for Majorana DM models, given that the enhanced rate to radiated W and Z gauge bosons and their dominant decay via hadronic channels tends to produce more anti-protons than are observed.
Comments: 22 pages, including five sets of figures and two tables; expands upon talk presented at the CETUP* Dark Matter Workshop, Lead, South Dakota, July 2012
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:1301.0021 [hep-ph]
  (or arXiv:1301.0021v1 [hep-ph] for this version)
  https://doi.org/10.48550/arXiv.1301.0021
Related DOI: https://doi.org/10.1063/1.4807354

Submission history

From: Thomas J. Weiler [view email]
[v1] Mon, 31 Dec 2012 22:06:31 UTC (495 KB)
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