Dark Matter Annihilation Signatures from Electroweak Bremsstrahlung

TL;DR

This paper investigates how electroweak bremsstrahlung in dark matter annihilation produces observable signals like gamma rays and cosmic rays, setting limits on dark matter models based on astrophysical data.

Contribution

It demonstrates that electroweak bremsstrahlung can dominate dark matter annihilation channels and calculates the resulting spectra of stable particles, providing new constraints from cosmic ray observations.

Findings

Electroweak bremsstrahlung significantly enhances dark matter annihilation signals.

Cosmic ray antiproton data strongly constrains models with dominant bremsstrahlung channels.

Sizable dark matter contributions to positron fluxes are excluded in these models.

Abstract

We examine observational signatures of dark matter annihilation in the Milky Way arising from electroweak bremsstrahlung contributions to the annihilation cross section. It has been known for some time that photon bremsstrahlung may significantly boost DM annihilation yields. Recently, we have shown that electroweak bremsstrahlung of W and Z gauge bosons can be the dominant annihilation channel in some popular models with helicity-suppressed 2 --> 2 annihilation. W/Z-bremsstrahlung is particularly interesting because the gauge bosons produced via annihilation subsequently decay to produce large correlated fluxes of electrons, positrons, neutrinos, hadrons (including antiprotons) and gamma rays, which are all of importance in indirect dark matter searches. Here we calculate the spectra of stable annihilation products produced via gamma/W/Z-bremsstrahlung. After modifying the fluxes to account for the propagation through the Galaxy, we set upper bounds on the annihilation cross section via a comparison with observational data. We show that stringent cosmic ray antiproton limits preclude a sizable dark matter contribution to observed cosmic ray positron fluxes in the class of models for which the bremsstrahlung processes dominate.