Phenomenology of dark matter annihilation into a long-lived intermediate state

Abstract

We propose a scenario where Dark Matter (DM) annihilates into an intermediate state which travels a distance λ ≡ v/Γ on the order of galactic scales and then decays to Standard Model (SM) particles. The long lifetime disperses the production zone of the SM particles away from the galactic center and hence, relaxes constraints from gamma ray observations on canonical annihilation scenarios. We utilize this set up to explain the electron and positron excesses observed recently by PAMELA, ATIC and FERMI. While an explanation in terms of usual DM annihilations seems to conflict with gamma ray observations, we show that within the proposed scenario, the PAMELA/ATIC/FERMI results are consistent with the gamma ray data. The distinction from decay scenarios is discsussed and we comment on the prospects for DM production at LHC. The typical decay length λ 10 kpc of the intermediate state can have its origin from a dimension six operator suppressed by a scale Λ ∼ 10 13 GeV, which is roughly the seesaw scale for neutrino masses. © 2009 IOP Publishing Ltd and SISSA.