Dark Matter Signals from Cascade Annihilations

TL;DR

This paper explores how cascade annihilation models of dark matter can explain cosmic ray excesses while satisfying gamma ray and neutrino constraints, highlighting the impact of decay steps and channels on observational signals.

Contribution

It analyzes the effects of cascade annihilations on gamma ray and neutrino constraints, introducing models that fit electron/positron data and soften gamma ray limits.

Findings

Cascade annihilations can fit PAMELA and ATIC data.

Cascade models soften gamma ray constraints by an order of magnitude.

Neutrino constraints remain robust for muon-dominated channels.

Abstract

A leading interpretation of the electron/positron excesses seen by PAMELA and ATIC is dark matter annihilation in the galactic halo. Depending on the annihilation channel, the electron/positron signal could be accompanied by a galactic gamma ray or neutrino flux, and the non-detection of such fluxes constrains the couplings and halo properties of dark matter. In this paper, we study the interplay of electron data with gamma ray and neutrino constraints in the context of cascade annihilation models, where dark matter annihilates into light degrees of freedom which in turn decay into leptons in one or more steps. Electron and muon cascades give a reasonable fit to the PAMELA and ATIC data. Compared to direct annihilation, cascade annihilations can soften gamma ray constraints from final state radiation by an order of magnitude. However, if dark matter annihilates primarily into muons, the neutrino constraints are robust regardless of the number of cascade decay steps. We also examine the electron data and gamma ray/neutrino constraints on the recently proposed "axion portal" scenario.