On the role of electroweak bremsstrahlung for indirect dark matter signatures

TL;DR

Electroweak bremsstrahlung significantly impacts the predicted signals of dark matter annihilation, especially in models producing leptons, altering the expected cosmic ray and gamma-ray signatures crucial for indirect detection.

Contribution

This paper demonstrates that electroweak bremsstrahlung effects must be included in dark matter indirect detection predictions, especially for leptonic final states, revealing potential biases in previous analyses.

Findings

Electroweak bremsstrahlung affects branching ratios and spectral shapes.

Significant modifications to multimessenger signals in leptonic dark matter models.

Potential biases in dark matter indirect detection results when neglecting electroweak effects.

Abstract

Interpretations of indirect searches for dark matter (DM) require theoretical predictions for the annihilation or decay rates of DM into stable particles of the standard model. These predictions include usually only final states accessible as lowest order tree-level processes, with electromagnetic bremsstrahlung and the loop-suppressed two gamma-ray line as exceptions. We show that this restriction may lead to severely biased results for DM tailored to produce only leptons in final states and with mass in the TeV range. For such models, unavoidable electroweak bremsstrahlung of Z and W-bosons has a significant influence both on the branching ratio and the spectral shape of the final state particles. We work out the consequences for two situations: Firstly, the idealized case where DM annihilates at tree level with 100% branching ratio into neutrinos. For a given cross section, this leads eventually to "minimal yields" of photons, electrons, positrons and antiprotons. Secondly, the case where the only allowed two-body final states are electrons. The latter case is typical of models aimed at fitting cosmic ray e^- and e^+ data. We find that the multimessenger signatures of such models can be significantly modified with respect to results presented in the literature.