Pamela, FGST and Sub-Tev Dark Matter

TL;DR

This paper investigates whether dark matter particles with masses around 300 GeV can explain the PAMELA positron excess, considering Fermi's electron spectrum data and astrophysical factors.

Contribution

It revisits Fermi's electron spectrum in the context of dark matter annihilation, showing lighter dark matter particles than previously thought can account for observations.

Findings

Dark matter particles as light as ~300 GeV can explain PAMELA's positron excess.

Astrophysical background variations and detector resolution affect dark matter mass constraints.

Reassessment of dark matter mass range compatible with cosmic ray data.

Abstract

PAMELA's observation that the cosmic ray positron fraction increases rapidly with energy implies the presence of primary sources of energetic electron-positron pairs. Of particular interest is the possibility that dark matter annihilations in the halo of the Milky Way provide this anomalous flux of antimatter. The recent measurement of the cosmic ray electron spectrum by the Fermi Gamma Ray Space Telescope, however, can be used to constrain the nature of any such dark matter particle. In particular, it has been argued that in order to accommodate the observations of Fermi and provide the PAMELA positron excess, annihilating dark matter particles must be as massive as ~1 TeV or heavier. In this article, we revisit Fermi's electron spectrum measurement within the context of annihilating dark matter, focusing on masses in the range of 100-1000 GeV, and considering effects such as variations in the astrophysical backgrounds from the presence of local cosmic ray accelerators, and the finite energy resolution of the Fermi Gamma Ray Space Telescope. When these factors are taken into account, we find that dark matter particles as light as ~300 GeV can be capable of generating the positron fraction observed by PAMELA.