Abstract
Electroweak corrections can play a crucial role in dark matter annihilation. The emission of gauge bosons, in particular, leads to a secondary flux consisting of all Standard Model particles, and may be described by electroweak fragmentation functions. To assess the quality of the fragmentation function approximation to electroweak radiation in dark matter annihilation, we have calculated the flux of secondary particles from gauge-boson emission in models with Majorana fermion and vector dark matter, respectively. For both models, we have compared cross sections and energy spectra of positrons and antiprotons after propagation through the galactic halo in the fragmentation function approximation and in the full calculation. Fragmentation functions fail to describe the particle fluxes in the case of Majorana fermion annihilation into light fermions: the helicity suppression of the lowest-order cross section in such models cannot be lifted by the leading logarithmic contributions included in the fragmentation function approach. However, for other classes of models like vector dark matter, where the lowest-order cross section is not suppressed, electroweak fragmentation functions provide a simple, model-independent and accurate description of secondary particle fluxes.
Highlights
The existence of dark matter [1] provides strong evidence for physics beyond the Standard Model (SM)
We show that the fragmentation function approach reproduces well the exact result in the case of universal extra dimensions (UED) with vector dark matter, while the approximation does not work for the minimal supersymmetric model (MSSM) with Majorana fermion annihilation into electron-positron pairs
In order to quantify the accuracy of the fragmentation function approximation, we have calculated dark matter annihilation into an e+e−-pair plus a Z boson, DM DM → e+e−Z, in the minimal supersymmetric model (MSSM) with neutralino dark matter and in a model with universal extra dimensions (UED), where the dark matter is provided by the first KaluzaKlein excitation of the photon
Summary
The existence of dark matter [1] provides strong evidence for physics beyond the Standard Model (SM). We show that the fragmentation function approach reproduces well the exact result in the case of UED with vector dark matter, while the approximation does not work for the MSSM with Majorana fermion annihilation into electron-positron pairs This is due to the fact that the annihilation of Majorana fermions into a light lepton pair is helicity suppressed and that the emission of soft and collinear gauge bosons from the final-state particles, included in the fragmentation function approximation, is not sufficient to lift this helicity suppression [16].
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