2,304 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
Cosmology with two compactification scales
We consider a (4+d)-dimensional spacetime broken up into a (4-n)-dimensional
Minkowski spacetime (where n goes from 1 to 3) and a compact (n+d)-dimensional
manifold. At the present time the n compactification radii are of the order of
the Universe size, while the other d compactification radii are of the order of
the Planck length.Comment: 16 pages, Latex2e, 7 figure
Mass - concentration relation and weak lensing peak counts
The statistics of peaks in weak lensing convergence maps is a promising tool
to investigate both the properties of dark matter haloes and constrain the
cosmological parameters. We study how the number of detectable peaks and its
scaling with redshift depend upon the cluster dark matter halo profiles and use
peak statistics to constrain the parameters of the mass - concentration (MC)
relation. We investigate which constraints the Euclid mission can set on the MC
coefficients also taking into account degeneracies with the cosmological
parameters. To this end, we first estimate the number of peaks and its redshift
distribution for different MC relations. We find that the steeper the mass
dependence and the larger the normalisation, the higher is the number of
detectable clusters, with the total number of peaks changing up to
depending on the MC relation. We then perform a Fisher matrix forecast of the
errors on the MC relation parameters as well as cosmological parameters. We
find that peak number counts detected by Euclid can determine the normalization
, the mass and redshift slopes and intrinsic scatter
of the MC relation to an unprecedented accuracy being
, , ,
if all cosmological parameters are assumed to
be known. Should we relax this severe assumption, constraints are degraded, but
remarkably good results can be restored setting only some of the parameters or
combining peak counts with Planck data. This precision can give insight on
competing scenarios of structure formation and evolution and on the role of
baryons in cluster assembling. Alternatively, for a fixed MC relation, future
peaks counts can perform as well as current BAO and SNeIa when combined with
Planck.Comment: 14 pages, 8 figures, accepted for publication on Astronomy &
Astrophysic
The HH34 outflow as seen in [FeII]1.64um by LBT-LUCI
Dense atomic jets from young stars copiously emit in [FeII] IR lines, which
can, therefore, be used to trace the immediate environments of embedded
protostars. We want to investigate the morphology of the bright [FeII] 1.64um
line in the jet of the source HH34 IRS and compare it with the most commonly
used optical tracer [SII]. We analyse a 1.64um narrow-band filter image
obtained with the Large Binocular Telescope (LBT) LUCI instrument, which covers
the HH34 jet and counterjet. A Point Spread Function (PSF) deconvolution
algorithm was applied to enhance spatial resolution and make the IR image
directly comparable to a [SII] HST image of the same source. The [FeII]
emission is detected from both the jet, the (weak) counter-jet, and from the
HH34-S and HH34-N bow shocks. The deconvolved image allows us to resolve jet
knots close to about 1\arcsec from the central source. The morphology of the
[FeII] emission is remarkably similar to that of the [SII] emission, and the
relative positions of [FeII] and [SII] peaks are shifted according to proper
motion measurements, which were previously derived from HST images. An analysis
of the [FeII]/[SII] emission ratio shows that Fe gas abundance is much lower
than the solar value with up to 90% of Fe depletion in the inner jet knots.
This confirms previous findings on dusty jets, where shocks are not efficient
enough to remove refractory species from grains.Comment: 5 pages, 4 figures, note accepted by A&
The effective Equation of State in Palatini cosmology
We investigate how the cosmological Equation of State can be used for
scrutinizing extended theories of gravity, in particular, the Palatini
gravity. Specifically, the approach consists, at first, in investigating the
effective Equation of State produced by a given model. Then, the inverse
problem can also be considered in view of determining which models are
compatible with a given effective Equation of State. We consider and solve some
cases and show that, for example, power-law models are (the only models)
capable of transforming barotropic Equations of State into effective barotropic
ones. Moreover, the form of Equation of State is preserved (only) for ,
as expected. In this perspective, modified Equations of State are a feature
capable of distinguishing Extended Gravity with respect to General Relativity.
We also investigate quadratic and non-homogeneous effective Equations of State
showing, in particular, that they contain the Starobinsky model and other ones.Comment: 19 page
Applicability of shape parameterizations for giant dipole resonance in warm and rapidly rotating nuclei
We investigate how well the shape parameterizations are applicable for
studying the giant dipole resonance (GDR) in nuclei, in the low temperature
and/or high spin regime. The shape fluctuations due to thermal effects in the
GDR observables are calculated using the actual free energies evaluated at
fixed spin and temperature. The results obtained are compared with Landau
theory calculations done by parameterizing the free energy. We exemplify that
the Landau theory could be inadequate where shell effects are dominating. This
discrepancy at low temperatures and high spins are well reflected in GDR
observables and hence insists on exact calculations in such cases.Comment: 10 pages, 2 figure
Rate-of-Return Dominance and Efficiency in an Experimental Economy.
One of the main challenges for monetary economics is to explain the use of assets that are dominated in rate-of-return as media of exchange. In this paper, we use experimental methods to study how a fiat money might come to be used in transactions when an identically marketable, dividend-bearing asset, a consol, is also available.EXPERIMENTS ; ECONOMICS ; MONEY
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
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