Recently, detections of a high-energy gamma-ray source at the position of the Galactic center have been reported by multiple gamma-ray telescopes, spanning the energy range between 100 MeV and 100 TeV. Analysis of these signals strongly suggests the
TeV emission to have a morphology consistent with a point source up to the angular resolution of the HESS telescope (approximately 3 pc), while the point-source nature of the GeV emission is currently unsettled, with indications that it may be spatially extended. In the case that the emission is hadronic and in a steady state, we show that the expected gamma-ray morphology is dominated by the distribution of target gas, rather than by details of cosmic-ray injection and propagation. Specifically, we expect a significant portion of hadronic emission to coincide with the position of the circum-nuclear ring, which resides between 1-3 pc from the Galactic center. We note that the upcoming Cherenkov Telescope Array (CTA) will be able to observe conclusive correlations between the morphology of the TeV gamma-ray source and the observed gas density, convincingly confirming or ruling out a hadronic origin for the gamma-ray emission.
We address the question of whether the upcoming generation of dark matter search experiments and colliders will be able to discover if the dark matter in the Universe has two components of weakly interacting massive particles (WIMPs). We outline a mo
del-independent approach, and we study the specific cases of (1) direct detection with low-background 1 ton noble-gas detectors and (2) a 0.5 TeV center of mass energy electron-positron linear collider. We also analyze the case of indirect detection via two gamma-ray lines, which would provide a verification of such a discovery, although multiple gamma-ray lines can in principle originate from the annihilation of a single dark matter particle. For each search channel, we outline a few assumptions to relate the very small set of parameters we consider (defining the masses of the two WIMPs and their relative abundance in the overall dark matter density) with the relevant detection rates. We then draw general conclusions on which corners of a generic dual-component dark matter scenario can be explored with current and next generation experiments. We find that in all channels the ideal setup is one where the relative mass splitting between the two WIMP species is of order 1, and where the two dark matter components contribute in a ratio close to 1:1 to the overall dark matter content of the Universe. Interestingly, in the case of direct detection, future experiments might detect multiple states even if only ~ 10% of the energy-density of dark matter in the Universe is in the subdominant species.
Several recent studies have considered modifications to the standard weakly-interacting massive particle (WIMP) scenario in which the cross section (times relative velocity v) for pair annihilation is enhanced by a factor 1/v. Since v~10^{-3} in the
Galactic halo, this may boost the annihilation rate into photons and/or electron-positron pairs enough to explain several puzzling Galactic radiation signals. Here we show that if the annihilation cross section scales as 1/v, then there is a burst of WIMP annihilation in the first dark-matter halos that form at redshifts z ~ 100-200. If the annihilation is to gamma rays in the energy range 100 keV - 300 GeV, or to electron-positron pairs in the energy range GeV - 2 TeV, then there remains a contribution to the diffuse extragalactic gamma-ray background today. Upper limits to this background provide constraints to the annihilation cross section. If the photon or electron-positron energies fall outside these energy ranges, then the radiation is absorbed by the intergalactic medium (IGM) and thus ionizes and heats the IGM. In this case, cosmic microwave background constraints to the ionization history also put limits on the annihilation cross section.
We investigate a scenario where the recently discovered non-thermal hard X-ray emission from the Ophiuchus cluster originates from inverse Compton scattering of energetic electrons and positrons produced in weakly interacting dark matter pair annihil
ations. We show that this scenario can account for both the X-ray and the radio emission, provided the average magnetic field is of the order of 0.1 microGauss. We demonstrate that GLAST will conclusively test the dark matter annihilation hypothesis. Depending on the particle dark matter model, GLAST might even detect the monochromatic line produced by dark matter pair annihilation into two photons.
