Dark Matter interpretations of the e^± excesses after FERMI

The cosmic-ray excess observed by PAMELA in the positron fraction and by FERMI and HESS in e^- + e⁺ can be interpreted in terms of DM annihilations or decays into leptonic final states. Final states into τ's or 4μ give the best-fit to the excess. However, in the annihilation scenario, they are incompatible with photon and neutrino constraints, unless DM has a quasi-constant density profile. Final states involving e's are less constrained but poorly fit the excess, unless hidden sector radiation makes their energy spectrum smoother, allowing a fit to all the data with a combination of leptonic modes. In general, DM lighter than about a TeV cannot fit the excesses, so PAMELA should find a greater positron fraction at higher energies. The DM interpretation can be tested by FERMI γ observations above 10 GeV: if the e^± excess is everywhere in the DM halo, Inverse Compton scattering on ambient light produces a well-predicted γ excess that FERMI should soon detect.