High energy positrons from annihilating dark matter

Abstract

We also consider a range of diffusion parameters consistent with current cosmic ray data. We find that a significant upturn in the positron fraction above 10 GeV is compatible with a wide range of dark matter annihilation modes, although very large annihilation cross sections and/or boost factors arising from inhomogeneities in the local dark matter distribution are required to produce the observed intensity of the signal. We comment on constraints from gamma rays, synchrotron emission, and cosmic ray antiproton measurements. PACS numbers: 95.35.+d; 98.70.Sa; 96.50.S; 95.55.Vj FERMILAB-PUB-08-347-A Dark matter in the form of a thermal relic is an appealing explanation for the approximately 85% of the matter density of the universe not composed of baryons. In addition to being a natural extension of the big bang cosmology, the candidates which naturally give the appropriate relic abundance have annihilation cross sections of the order of the electroweak scale, a natural scale for new particles in theoretical frameworks which provide a solution to the hierarchy problem. If they exist, such thermal relics are expected to be annihilating in the halo today, generating potentially observable fluxes of high energy particles, including gamma rays, electrons, positrons, and antiprotons. To this end, a number of cosmic ray and gamma ray experiments [1, 2, 3, 4, 5, 6] have considered the search for dark matter annihilation products to be an important aspect of their science mission. Of particular interest is the satellite-based cosmic ray experiment, PAMELA [7, 8]. With its large acceptance (21.5 cm 2 sr) and excellent particle identification, PAMELA is anticipated to measure the spectra of cosmic ray protons, antiprotons, electrons and positrons up to energies of 700 GeV, 190 GeV, 2 TeV and 270 GeV, respectively.