Cosmic ray lepton puzzle in the light of cosmological N-body simulations

TL;DR

This paper investigates whether dark matter subhalos could explain cosmic ray lepton anomalies, finding that such explanations are highly improbable based on cosmological simulations and predicting gamma-ray detection by Fermi.

Contribution

The study combines cosmic ray data analysis with cosmological N-body simulations to assess the likelihood of dark matter subhalos causing observed anomalies.

Findings

Nearby dark matter subhalos are unlikely sources of the anomalies.

Reproducing the anomalies requires very improbable subhalo configurations.

Fermi is predicted to detect gamma-ray emission from such subhalos.

Abstract

The PAMELA and ATIC collaborations have recently reported an excess in the cosmic ray positron and electron fluxes. These lepton anomalies might be related to cold dark matter (CDM) particles annihilating within a nearby dark matter clump. We outline regions of the parameter space for both the dark matter subhalo 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 II. Having a sizable clump (Vmax = 9km/s) 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 subhalo, which is extremely unlikely (p~3.10^-5). In either case, we predict Fermi will detect the gamma-ray emission from the subhalo. We conclude that under canonical assumptions, the cosmic ray lepton anomalies are unlikely to originate from a nearby CDM subhalo.