842 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
A dark matter interpretation for the ARCADE excess?
The ARCADE 2 Collaboration has recently measured an isotropic radio emission
which is significantly brighter than the expected contributions from known
extra-galactic sources. The simplest explanation of such excess involves a
"new" population of unresolved sources which become the most numerous at very
low (observationally unreached) brightness. We investigate this scenario in
terms of synchrotron radiation induced by WIMP annihilations or decays in
extragalactic halos. Intriguingly, for light-mass WIMPs with thermal
annihilation cross-section, and fairly conservative clustering assumptions, the
level of expected radio emission matches the ARCADE observations.Comment: 5 pages, 3 figures. v2: one benchmark model added, comments and
references expanded, to appear in PR
Evidence of cross-correlation between the CMB lensing and the gamma-ray sky
We report the measurement of the angular power spectrum of cross-correlation
between the unresolved component of the Fermi-LAT gamma-ray sky-maps and the
CMB lensing potential map reconstructed by the Planck satellite. The matter
distribution in the Universe determines the bending of light coming from the
last scattering surface. At the same time, the matter density drives the growth
history of astrophysical objects, including their capability at generating
non-thermal phenomena, which in turn give rise to gamma-ray emissions. The
Planck lensing map provides information on the integrated distribution of
matter, while the integrated history of gamma-ray emitters is imprinted in the
Fermi-LAT sky maps. We report here the first evidence of their correlation. We
find that the multipole dependence of the cross-correlation measurement is in
agreement with current models of the gamma-ray luminosity function for AGN and
star forming galaxies, with a statistical evidence of 3.0. Moreover,
its amplitude can in general be matched only assuming that these extra-galactic
emitters are also the bulk contribution of the measured isotopic gamma-ray
background (IGRB) intensity. This leaves little room for a big contribution
from galactic sources to the IGRB measured by Fermi-LAT, pointing toward a
direct evidence of the extragalactic origin of the IGRB.Comment: 6 pages, 2 figures. v2: analysis updated with Planck 2015 lensing map
and 3FGL catalogue, conclusions strengthened; to appear in ApJ Letter
Long-Range Forces in Direct Dark Matter Searches
We discuss the positive indications of a possible dark matter signal in
direct detection experiments in terms of a mechanism of interaction between the
dark matter particle and the nuclei occurring via the exchange of a light
mediator, resulting in a long-range interaction. We analyze the annual
modulation results observed by the DAMA and CoGeNT experiments and the observed
excess of events of CRESST. In our analysis, we discuss the relevance of
uncertainties related to the velocity distribution of galactic dark matter and
to the channeling effect in NaI. We find that a long-range force is a viable
mechanism, which can provide full agreement between the reconstructed dark
matter properties from the various experimental data sets, especially for
masses of the light mediator in the 10-30 MeV range and a light dark matter
with a mass around 10 GeV. The relevant bounds on the light mediator mass and
scattering cross section are then derived, should the annual modulation effects
be due to this class of long-range forces.Comment: 22 pages, 14 figures. v2: Matches version published on Phys.Rev.D;
analysis of CRESST to match the recent release of the new data updated,
discussion on astrophysical constraints on self-interacting dark matter
added, some typos corrected and some references added, conclusions unchanged.
v3: Few typos correcte
Red Alert: a cognitive countermeasure to mitigate attentional tunneling
Attentional tunneling, that is the inability to detect unexpected changes in the environment, has been shown to have critical consequences in air traffic control. The motivation of this study was to assess the design of a cognitive countermeasure dedicated to mitigate such failure of attention. The Red Alert cognitive countermeasure relies on a brief orange-red flash (300 ms) that masks the entire screen with a 15% opacity. Twenty-two air traffic controllers faced two demanding scenarios, with or without the cognitive countermeasure. The volunteers were not told about the Red Alert so as to assess the intuitiveness of the design without prior knowledge. Behavioral results indicated that the cognitive countermeasure reduced reaction time and improved the detection of the notification when compared to the classical operational design. Further analyses showed this effect was even stronger for half of our participants (91.7% detection rate) who intuitively understood the purpose of this design
Insertion of Iron Decorated Organic-Inorganic Cage-Like Polyhedral Oligomeric Silsesquioxanes between Clay Platelets by Langmuir Schaefer Deposition
Tuning the architecture of multilayer nanostructures by exploiting the properties of their constituents is a versatile way to develop multifunctional films. Herein, we report a bottom-up approach for the fabrication of highly ordered hybrid films consisting of dimethyldioctadecylammonium (DODA), iron decorated polyhedral oligomeric silsesquioxanes (POSS), and montmorillonite clay platelets. Clay platelets provided the template where Fe/POSS moieties were grafted by the use of the surfactant. Driven by the iron ions present, DODA adopted a staggered arrangement, which is essential to realize the controllable layer-by-layer growth of the film. The elemental composition of the film was studied by X-ray photoelectron spectroscopy and X-ray reflectivity confirmed the existence of smooth interfaces between the different layers
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