Gamma-ray signatures of annihilation to charged leptons in dark matter substructure

TL;DR

This paper investigates gamma-ray signals from dark matter annihilation into charged leptons within Milky Way subhalos, highlighting their potential to explain the positron excess and constrain models using gamma-ray and cosmic-ray data.

Contribution

It demonstrates how substructure enhances gamma-ray signatures from dark matter annihilation and explores constraints from gamma-ray background and cosmic-ray measurements.

Findings

Subhalos can significantly contribute to the positron excess.

Diffuse inverse-Compton emission from substructure is nearly isotropic.

HESS cosmic-ray data constrains multi-TeV gamma-ray signals.

Abstract

Due to their higher concentrations and small internal velocities, Milky Way subhalos can be at least as important as the smooth halo in accounting for the GeV positron excess via dark matter annihilation. After showing how this can be achieved in various scenarios, including in Sommerfeld models, we demonstrate that, in this case, the diffuse inverse-Compton emission resulting from electrons and positrons produced in substructure leads to a nearly-isotropic signal close to the level of the isotropic GeV gamma-ray background seen by Fermi. Moreover, we show that HESS cosmic-ray electron measurements can be used to constrain multi-TeV internal bremsstrahlung gamma rays arising from annihilation to charged leptons.