Astrophysical boost factor and dark matter indirect detection

Abstract

The PAMELA [1], ATIC[2] and Fermi[3] collaborations have recently reported an excess in the cosmic ray positron and electron fluxes. These lepton anomalies might be related to cold dark matter particles annihilating within a nearby dark matter sub-halo. We outline regions of the parameter space for both the dark matter sub-halo and particle model, where data from the different experiments are reproduced. We then confront this interpretation of the data with the results of the cosmological N-body simulation Via Lactea 2. Having a sizeable sub-halo at a distance of only 1.2 kpc could explain the PAMELA excess, but such a configuration has a probability of only 0.37 percent. Reproducing also the ATIC bump would require a very large, nearby sub-halo, which is extremely unlikely (p ~ 3 × 10−5). It is even less probable for the smaller Fermi bump to be caused by the presence of such an object. In either case, we predict Fermi will detect the gamma-ray emission from the sub-halo. We conclude that under canonical assumptions, the cosmic ray lepton anomalies are unlikely to originate from a nearby cold Dark Matter sub-halo.