We perform a detailed study of the sensitivity to the anisotropies related to Dark Matter (DM) annihilation in the Isotropic Gamma-Ray Background (IGRB) as measured by the Fermi Large Area Telescope ...(Fermi-LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi-LAT. We consider DM anisotropies of extra-galactic origin and of Galactic origin (which can be generated through annihilation in the Milky Way sub-structures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 years of observation Fermi is sensitive to a DM contribution at the level of the thermal-relic cross section depending on the DM mass and annihilation mode. The anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle. (abridged)
This chapter discusses the Braneworld models that solve the hierarchy problem. The chapter focuses on Randall-Sundrum (RS) type models that embed one or two branes into a five dimensional AdS bulk. ...In RS 1, a static solution of the 5d Einstein equations is derived with two branes of opposite tension at the orbifold fixed points of the finite fifth dimension. Low-scale gravity leads to low reheating temperatures, and it is possible to obtain temperatures lower than the electroweak scale. This implies that the electroweak phase transition can take place before the completion of reheating. The chapter discusses how the gravitons couple in order to matter fields on the brane. The KK decomposition, graviton propagators and their coupling to matter and gauge fields are considered for toroidal extra dimensions and the analysis for the infinite AdS bulks have to be repeated.
This work investigates the dark matters structures that form on the smallest cosmological scales. We find that the types and abundances of structures which form at approximately Earth-mass scales are ...very sensitive to the nature of dark matter. We explore various candidates for dark matter and determine the corresponding properties of small-scale structure. In particular, we discuss possibilities for indirect detection of dark matter through small-scale structure, and comment on the potential of these methods for discriminating between dark matter candidates.
Measurement of the extragalactic background (EGBR) of diffuse gamma-rays is perhaps one of the most challenging tasks for future gamma-ray observatories, such as GLAST. This is because any ...determination will depend on accurate subtraction of the galactic diffuse and celestial foregrounds, as well as point sources. However, the EGBR is likely to contain very rich information about the high energy-gamma ray sources of the Universe at cosmological distances. We focus on the ability of GLAST to detect a signal from dark matter in the EGBR. We present sensitivities for generic thermal WIMPs and the Inert Higgs Doublet Model. Also we discuss the various aspects of astrophysics and particle physics that determines the shape and strength of the signal, such as dark matter halo properties and different dark matter candidates. Other possible sources to the EGBR are also discussed, such as unresolved AGNs, and viewed as backgrounds.
This work investigates the dark matters structures that form on the smallest
cosmological scales. We find that the types and abundances of structures which
form at approximately Earth-mass scales are ...very sensitive to the nature of
dark matter. We explore various candidates for dark matter and determine the
corresponding properties of small-scale structure. In particular, we discuss
possibilities for indirect detection of dark matter through small-scale
structure, and comment on the potential of these methods for discriminating
between dark matter candidates.
The first published Fermi large area telescope (Fermi-LAT) measurement of the isotropic diffuse gamma-ray emission is in good agreement with a single power law, and is not showing any signature of a ...dominant contribution from dark matter sources in the energy range from 20 to 100 GeV. We use the absolute size and spectral shape of this measured flux to derive cross section limits on three types of generic dark matter candidates: annihilating into quarks, charged leptons and monochromatic photons. Predicted gamma-ray fluxes from annihilating dark matter are strongly affected by the underlying distribution of dark matter, and by using different available results of matter structure formation we assess these uncertainties. We also quantify how the dark matter constraints depend on the assumed conventional backgrounds and on the Universe's transparency to high-energy gamma-rays. In reasonable background and dark matter structure scenarios (but not in all scenarios we consider) it is possible to exclude models proposed to explain the excess of electrons and positrons measured by the Fermi-LAT and PAMELA experiments. Derived limits also start to probe cross sections expected from thermally produced relics (e.g. in minimal supersymmetry models) annihilating predominantly into quarks. For the monochromatic gamma-ray signature, the current measurement constrains only dark matter scenarios with very strong signals.
Dark matter (DM) particle annihilation or decay can produce monochromatic \(\gamma\)-rays readily distinguishable from astrophysical sources. \(\gamma\)-ray line limits from 30 GeV to 200 GeV ...obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a \(\gamma\)-ray line analysis, and integrated over most of the sky. We obtain \(\gamma\)-ray line flux upper limits in the range \(0.6-4.5\times 10^{-9}\mathrm{cm}^{-2}\mathrm{s}^{-1}\), and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.
We report on the observations of 14 dwarf spheroidal galaxies with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope provides a new ...opportunity to test particle dark matter models through the expected gamma-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant gamma-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the gamma-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10^-9 photons cm^-2 s^-1. Using recent stellar kinematic data, the gamma-ray flux limits are combined with improved determinations of the dark matter density profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilation cross-section of WIMPs in several widely studied extensions of the standard model. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g. in models where supersymmetry breaking occurs via anomaly mediation. The gamma-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e^+e^- data, including low-mass wino-like neutralinos and models with TeV masses pair-annihilating into muon-antimuon pairs. (Abridged)
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