Weak Corrections are Relevant for Dark Matter Indirect Detection

TL;DR

This work demonstrates that electroweak radiative corrections become phenomenologically relevant for dark matter indirect detection when the DM mass $M$ exceeds the electroweak scale $M_W$. By formulating a model-independent EW fragmentation framework and solving leading-log EW evolution, the authors show that soft $W$/$Z$ emission opens new decay/annihilation channels and distributes energy among all SM final states, significantly altering spectra, especially at low energies. The approach combines analytic EW splitting functions with MC-generated spectra, and is validated against full three-body calculations in Minimal Dark Matter, showing an overall doubling of yields and the emergence of low-energy tails in $e^+$, $\gamma$, and $\bar p$. These results imply that EW corrections must be included in DM indirect-detection analyses to accurately predict fluxes and interpret data from PAMELA, Fermi-LAT, and similar experiments. The framework provides practical ingredients for incorporating EW effects into predictions without full Monte Carlo reweighting, improving the reliability of DM searches at the TeV scale.

Abstract

The computation of the energy spectra of Standard Model particles originated from the annihilation/decay of dark matter particles is of primary importance in indirect searches of dark matter. We compute how the inclusion of electroweak corrections significantly alter such spectra when the mass M of dark matter particles is larger than the electroweak scale: soft electroweak gauge bosons are copiously radiated opening new channels in the final states which otherwise would be forbidden if such corrections are neglected. All stable particles are therefore present in the final spectrum, independently of the primary channel of dark matter annihilation/decay. Such corrections are model independent.

Figures (7)

• Figure 1: DM annihilation/decay initially produces a hard positron-electron pair. The spectrum of the hard objects is altered by electroweak virtual corrections (green photon line) and real $Z$ emission. The $Z$ decays hadronically through a $q\bar{q}$ pair and produces a great number of much softer objects, among which an antiproton and two pions; the latter cascade decay to softer $\gamma$s and leptons.
• Figure 2: Splitting function between massive vectors. Blue curve: naive result. Dashed curve: our result. Red curve: full 3-body result in the Minimal Dark Matter model.
• Figure 3: Comparison between spectra with (continuous lines) and without EW corrections (dashed). We show the following final states: $e^+$ (green), $\bar{p}$ (blue), $\gamma$ (red), $\nu = (\nu_e +\nu_\mu+\nu_\tau)/3$ (black).
• Figure 4: DM signals in the $e^+$ (left) and $\bar{p}$ (right) fraction, with (dashed) and without (dot-dashed) electroweak corrections for two DM models that can fit the PAMELA $e^+$ excess: Minimal Dark Matter (upper) or a muonic channel (lower). The gray area is the predicted astrophysical background and the red area is the prediction adding the full DM contribution.
• Figure 5: Soft gauge boson real emission from spin-1 particle. It can be read as the sum of three scalar currents. Considering the process $\sqrt{s}\to p_1+k+p_2$ we show explicitly only the bremsstrahlung contribution from the $p_1$ final leg.