ATIC, PAMELA, HESS, Fermi and nearby Dark Matter subhalos

TL;DR

This paper examines how local dark matter subhalos and distribution inhomogeneities influence the electron and positron flux spectrum, with implications for interpreting cosmic ray data from multiple experiments.

Contribution

It analyzes the impact of dark matter models and subhalo clumps on the electron-positron flux spectrum, incorporating simulation data to estimate the likelihood of local clump effects.

Findings

Flux spectrum follows a universal power-law below a cutoff energy.

Dark matter subhalos can produce a harder electron-positron spectrum.

Probability of local subhalo effects is estimated between 4% and 15%.

Abstract

We study the local flux of electrons and positrons from annihilating Dark Matter (DM), and investigate how its spectrum depends on the choice of DM model and inhomogeneities in the DM distribution. Below a cutoff energy, the flux is expected to have a universal power-law form with an index n ~ -2. The cutoff energy and the behavior of the flux near the cutoff is model dependent. The dependence on the DM host halo profile may be significant at energies E < 100 GeV and leads to softening of the flux, n < -2. There may be additional features at high energies due to the presence of local clumps of DM, especially for models in which the Sommerfeld effect boosts subhalo luminosities. In general, the flux from a nearby clump gives rise to a harder spectrum of electrons and positrons, with an index n > -2. Using the Via Lactea II simulation, we estimate the probability of such subhalo effects in a generic Sommerfeld-enhanced model to be at least 4%, and possibly as high as 15% if subhalos below the simulation's resolution limit are accounted for. We discuss the consequences of these results for the interpretation of the ATIC, PAMELA, HESS, and Fermi data, as well as for future experiments.