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Register a new userIndirect Detection of Dark Matter Using MeV-Range Gamma-Ray Telescopes
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The astrophysics community is considering plans for a variety of gamma-ray telescopes (including ACT and GRIPS) in the energy range 1--100 MeV, which can fill in the so-called MeV gap in current sensitivity. We investigate the utility of such detectors for the study of low-mass dark matter annihilation or decay. For annihilating (decaying) dark matter with a mass below about 140 MeV (280 MeV) and couplings to first generation quarks, the final states will be dominated by photons or neutral pions, producing striking signals in gamma-ray telescopes. We determine the sensitivity of future detectors to the kinematically allowed final states. In particular, we find that planned detectors can improve on current sensitivity to this class of models by up to a few orders of magnitude.
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The extragalactic dark matter (DM) annihilation signal depends on the product of the clumping factor, <delta^2>, and the velocity-weighted annihilation cross section, sigma v. This clumping factor-sigma v degeneracy can be broken by comparing DM annihilation signals from multiple sources. In particular, one can constrain the minimum DM halo mass, M_min, which depends on the mass of the DM particles and the kinetic decoupling temperature, by comparing observations of individual DM sources to the diffuse DM annihilation signal. We demonstrate this with careful semi-analytic treatments of the DM contribution to the diffuse Isotropic Gamma-Ray Background (IGRB), and compare it with two recent hints of DM from the Galactic Center, namely, ~130 GeV DM annihilating dominantly in the chichi to gammagamma channel, and (10-30) GeV DM annihilating in the chichi to bbar{b} or chichi to tau^{+}tau^{-} channels. We show that, even in the most conservative analysis, the Fermi IGRB measurement already provides interesting sensitivity. A more detailed analysis of the IGRB, with new Fermi IGRB measurements and modeling of astrophysical backgrounds, may be able to probe values of M_min up to 1 M_sun for the 130 GeV candidate and 10^{-6} M_sun for the light DM candidates. Increasing the substructure content of halos by a reasonable amount would further improve these constraints.
The self-annihilation of dark matter particles with mass in the MeV range can produce gamma rays via prompt or secondary radiation. The annihilation rate for such light dark matter particles is however tightly constrained by cosmic microwave background (CMB) data. Here we explore the possibility of discovering MeV dark matter annihilation with future MeV gamma-ray telescopes taking into account the latest and future CMB constraints. We study the optimal energy window as a function of the dominant annihilation final state. We consider both the (conservative) case of the dwarf spheroidal galaxy Draco and the (more optimistic) case of the Galactic center. We find that for certain channels, including those with one or two monochromatic photon(s) and one or two neutral pion(s), a detectable gamma-ray signal is possible for both targets under consideration, and compatible with CMB constraints. For other annihilation channels, however, including all leptonic annihilation channels and two charged pions, CMB data rule out any significant signal of dark matter annihilation at future MeV gamma-ray telescopes from dwarf galaxies, but possibly not for the Galactic center.
This white paper describes the basic idea for indirect dark matter searches using antideuterons. Low energy antideuterons produced by dark matter annihilations/decays provide an attractive dark matter signature, due to the low astrophysical background. The current and future experiments have a strong potential to detect antideuterons from dark matter. They are complementary not only with each other, but also with other dark matter searches.
We describe a characteristic signature of dark matter (DM) annihilation or decay into gamma-rays. We show that if the total angular momentum of the initial DM particle(s) vanishes, and helicity suppression operates to prevent annihilation/decay into light fermion pairs, then the amplitude for the dominant 3-body final state f^+f^-gamma has a unique form dictated by gauge invariance. This amplitude and the corresponding energy spectra hold for annihilation of DM Majorana fermions or self-conjugate scalars, and for decay of DM scalars, thus encompassing a variety of possibilities. Within this scenario, we analyze Fermi LAT, PAMELA and HESS data, and predict a hint in future Fermi gamma-ray data that portends a striking signal at atmospheric Cherenkov telescopes (ACTs).
The details of what constitutes the majority of the mass that makes up dark matter in the Universe remains one of the prime puzzles of cosmology and particle physics today - eighty years after the first observational indications. Today, it is widely accepted that dark matter exists and that it is very likely composed of elementary particles - that are weakly interacting and massive (WIMPs for Weakly Interacting Massive Particles). As important as dark matter is in our understanding of cosmology, the detection of these particles has so far been elusive. Their primary properties such as mass and interaction cross sections are still unknown. Indirect detection searches for the products of WIMP annihilation or decay. This is generally done through observations of gamma-ray photons or cosmic rays. Instruments such as the Fermi-LAT, H.E.S.S., MAGIC and VERITAS, combined with the future Cherenkov Telescope Array (CTA) will provide important and complementary constraints to other search techniques. Given the expected sensitivities of all search techniques, we are at a stage where the WIMP scenario is facing stringent tests and it can be expected that WIMPs will be either be detected or the scenario will be so severely constrained that it will have to be re-thought. In this sense we are on the Threshold of Discovery. In this article, I will give a general overview over the current status and the future expectations for indirect searches for dark matter (WIMP) particles.
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