191 research outputs found
A novel approach in the WIMP quest: Cross-Correlation of Gamma-Ray Anisotropies and Cosmic Shear
Both cosmic shear and cosmological gamma-ray emission stem from the presence
of Dark Matter (DM) in the Universe: DM structures are responsible for the
bending of light in the weak lensing regime and those same objects can emit
gamma-rays, either because they host astrophysical sources (active galactic
nuclei or star-forming galaxies) or directly by DM annihilations (or decays,
depending on the properties of the DM particle). Such gamma-rays should
therefore exhibit strong correlation with the cosmic shear signal. In this
Letter, we compute the cross-correlation angular power spectrum of cosmic shear
and gamma-rays produced by the annihilation/decay of Weakly Interacting Massive
Particle (WIMP) DM, as well as from astrophysical sources. We show that this
observable provides novel information on the composition of the Extra-galactic
Gamma-ray Background (EGB), since the amplitude and shape of the
cross-correlation signal strongly depends on which class of source is
responsible for the gamma-ray emission. If the DM contribution to the EGB is
significant (at least in a definite energy range), although compatible with
current observational bounds, its strong correlation with the cosmic shear
makes such signal potentially detectable by combining Fermi-LAT data with
forthcoming galaxy surveys, like Dark Energy Survey and Euclid. At the same
time, the same signal would demonstrate that the weak lensing observables are
indeed due to particle DM matter and not to possible modifications of General
Relativity.Comment: 6 pages, 12 figures. v2: Matches version published in ApJ Lett. Text
reorganized, appendix removed (part of the discussion is now in the main
text), no major change
Anisotropy probe of galactic and extra-galactic Dark Matter annihilations
We study the flux and the angular power spectrum of gamma-rays produced by
Dark Matter (DM) annihilations in the Milky Way (MW) and in extra-galactic
halos. The annihilation signal receives contributions from: a) the smooth MW
halo, b) resolved and unresolved substructures in the MW, c) external DM halos
at all redshifts, including d) their substructures. Adopting a self-consistent
description of local and extra-galactic substructures, we show that the
annihilation flux from substructures in the MW dominates over all the other
components for angles larger than O(1) degrees from the Galactic Center, unless
an extreme prescription is adopted for the substructures concentration. We also
compute the angular power spectrum of gamma-ray anisotropies and find that, for
an optimistic choice of the particle physics parameters, an interesting
signature of DM annihilations could soon be discovered by the Fermi LAT
satellite at low multipoles, l<100, where the dominant contribution comes from
MW substructures with mass M>10^4 solar masses. For the substructures models we
have adopted, we find that the contribution of extra-galactic annihilations is
instead negligible at all scales.Comment: 14 pages, 7 figure
WIMP particle physics and astrophysics with direct detection and neutrino telescope data
With positive signals from multiple direct detection experiments it will, in principle, be possi- ble to measure the mass and cross sections of weakly-interacting massive particle (WIMP) dark matter. Recent work has shown that, with a polynomial parameterisation of the WIMP speed dis- tribution, it is possible to make an unbiased measurement of the WIMP mass, without making any astrophysical assumptions. However, direct detection experiments are not sensitive to low-speed WIMPs and, therefore, any model-independent approach will lead to a bias in the cross section. This problem can be solved with the addition of measurements of the flux of neutrinos from the Sun. This is because the flux of neutrinos produced from the annihilation of WIMPs which have been gravitationally captured in the Sun is sensitive to low-speed WIMPs. Using mock data from next-generation direct detection experiments and from the IceCube neutrino telescope, we show that the complementary information from IceCube on low-speed WIMPs breaks the degeneracy between the cross section and the speed distribution. This allows unbiased determinations of the WIMP mass and spin-independent and spin-dependent cross sections to be made, and the speed distribution to be reconstructed. We use two parameterisations of the speed distribution: binned and polynomial. While the polynomial parameterisation can encompass a wider range of speed distributions, this leads to larger uncertainties in the particle physics parameters
Primary Subcutaneous B-cell Lymphoma : Case Report and Literature Review
Primary cutaneous B-cell lymphomas are defined as malignant B-cell proliferations presenting with cutaneous involvement alone and no evidence of extracutaneous manifestations when complete staging has been performed. It has been shown that the infiltrate in some cases could involve the underlying subcutaneous tissues, but primary localization in this compartment has been rarely reported. We describe here the case of a 53-year-old woman who noticed a nodular lesion on the left shoulder that rapidly enlarged in a few months. The histological and immunophenotypical features were compatible with a subcutaneous B-cell lymphoma. The tumoural mass was confined predominantly to the subcutaneous compartment, as confirmed by computed tomography. No other tumour localizations were found. Thus, primary B-cell lymphoma of the subcutis was diagnosed. We report a review of the literature indicating that B-cell lymphomas that are primarily localized to the subcutaneous tissue represent a very rare modality of presentation with a biological behaviour different from conventional cutaneous B-cell lymphoma
How to calculate dark matter direct detection exclusion limits that are consistent with gamma rays from annihilation in the Milky Way halo
When comparing constraints on the weakly interacting massive particle (WIMP) properties from direct and indirect detection experiments it is crucial that the assumptions made about the dark matter (DM) distribution are realistic and consistent. For instance, if the Fermi-LAT Galactic center GeV gamma-ray excess was due to WIMP annihilation, its morphology would be incompatible with the standard halo model that is usually used to interpret data from direct detection experiments. In this article, we calculate exclusion limits from direct detection experiments using self-consistent velocity distributions, derived from mass models of the Milky Way where the DM halo has a generalized Navarro-Frenk-White profile. We use two different methods to make the mass model compatible with a DM interpretation of the Galactic center gamma-ray excess. First, we fix the inner slope of the DM density profile to the value that best fits the morphology of the excess. Second, we allow the inner slope to vary and include the morphology of the excess in the data sets used to constrain the gravitational potential of the Milky Way. The resulting direct detection limits differ significantly from those derived using the standard halo model, in particular for light WIMPs, due to the differences in both the local DM density and velocity distribution
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