Electroweak fragmentation functions for dark matter annihilation

TL;DR

This paper evaluates the effectiveness of electroweak fragmentation functions in predicting secondary particle fluxes from dark matter annihilation, finding they work well for some models but not for others with helicity suppression.

Contribution

It provides a comparative analysis of fragmentation functions versus full calculations for different dark matter models, highlighting their applicability and limitations.

Findings

Fragmentation functions fail for Majorana fermion models with light fermions.

They accurately describe vector dark matter annihilation fluxes.

Helicity suppression affects the validity of the fragmentation approach.

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.