77 research outputs found
Non-universal BBN bounds on electromagnetically decaying particles
In Poulin and Serpico [Phys. Rev. Lett. 114, 091101 (2015)] we have recently
argued that when the energy of a photon injected in the primordial plasma falls
below the pair-production threshold, the universality of the non-thermal photon
spectrum from the standard theory of electromagnetic cascades onto a photon
background breaks down. We showed that this could reopen or widen the parameter
space for an exotic solution to the 'lithium problem'. Here we discuss another
application, namely the impact that this has on non-thermal big bang
nucleosynthesis constraints from 4He, 3He and 2H, using the parametric example
of monochromatic photon injection of different energies. Typically, we find
tighter bounds than those existing in the literature, up to more than one order
of magnitude. As a consequence of the non-universality of the spectrum, the
energy-dependence of the photodissociation cross-sections is important. We also
compare the constraints obtained with current level and future reach of cosmic
microwave background spectral distortion bounds.Comment: 8 pages, 7 figures. v2: minor typographical corrections, extended
comments and reference
Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints
The very high energy Galactic -ray sky is partially opaque in the
() PeV energy range. In the light of the recently detected high energy
neutrino flux by IceCube, a comparable very high energy -ray flux is
expected in any scenario with a sizable Galactic contribution to the neutrino
flux. Here we elaborate on the peculiar energy and anisotropy features imposed
upon these very high energy -rays by the absorption on the cosmic
microwave background photons and Galactic interstellar light. As a notable
application of our considerations, we study the prospects of probing the
PeV-scale decaying DM scenario, proposed as a possible source of IceCube
neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular,
we show that anisotropy measurements at EAS experiments are already sensitive
to ~s and future measurements, using
better gamma/hadron separation, can improve the limit significantly.Comment: 23 pages, 9 figures; v2: the discussion of anisotropy in section 4
improved, matches the version published at JCA
Are IceCube neutrinos unveiling PeV-scale decaying dark matter?
Recent observations by IceCube, notably two PeV cascades accompanied by
events at energies ~ (30-400) TeV, are clearly in excess over atmospheric
background fluxes and beg for an astroparticle physics explanation. Although
some models of astrophysical accelerators can account for the observations
within current statistics, intriguing features in the energy and possibly
angular distributions of the events make worth exploring alternatives. Here, we
entertain the possibility of interpreting the data with a few PeV mass scale
decaying Dark Matter, with lifetime of the order of 10^27 s. We discuss generic
signatures of this scenario, including its unique energy spectrum distortion
with respect to the benchmark expectation for astrophysical
sources, as well as peculiar anisotropies. A direct comparison with the data
show a good match with the above-mentioned features. We further discuss
possible future checks of this scenario.Comment: 7 pages, 3 figures; v2: discussion improved, reference added, matches
the version published in JCA
Status of indirect dark matter detection
International audienceIndirect astrophysical channels (such as gamma rays, neutrinos, and cosmic ray antimatter) are a cornerstone in the dark matter particle identification program. A review of the present constraints is presented, together with some perspectives for the near future: we argue that the approach of "fitting any spectral feature to a dark matter model" is unlikely to lead to a convincing indirect detection of dark matter. Rather--if the WIMP paradigm for dark matter is correct--guidance from collider and direct detection programs is expected to allow soon for more fruitful a priori searches of correlated signatures in many indirect channels
Possible causes of a rise with energy of the cosmic ray positron fraction
Based on general considerations rather than model-dependent fits to specific
scenarios, we argue that an increase with energy of the positron fraction in
cosmic rays, suggested by several experiments at E>~7 GeV, most likely requires
a primary source of electron-positron pairs. We discuss the possible
alternatives, and find none of them plausible on astrophysical or particle
physics grounds. Further observational ways to test different scenarios are
discussed.Comment: 4 pages, 1 figure; minor changes, a few references added, matches
published versio
Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?
Several groups have recently claimed evidence for an unaccounted gamma-ray
excess over {the} diffuse backgrounds at few GeV in {the} Fermi-LAT data in a
region around the Galactic Center, consistent with a dark matter annihilation
origin. We demonstrate that the main spectral and angular features of this
excess can be reproduced if they are mostly due to inverse Compton emission
from high-energy electrons injected in a burst event of ~10^52 - 10^53erg
roughly O(10^6) years ago. We consider this example as a proof of principle
that time-dependent phenomena need to be understood and accounted for -
together with detailed diffuse foregrounds and unaccounted "steady state"
astrophysical sources - before any robust inference can be made about dark
matter signals at the Galactic Center. In addition, we point out that the
timescale suggested by our study, which controls both the energy cutoff and the
angular extension of the signal, intriguingly matches (together with the energy
budget) what is indirectly inferred by other evidences suggesting a very active
Galactic Center in the past, for instance related to intense star formation and
accretion phenomena.Comment: 6 pages, 4 figures. Minor scale correction plus a typo in a figure
label. Conclusions unchange
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Angular Signatures of Dark Matter in the Diffuse Gamma Ray Spectrum
Dark matter annihilating in our Galaxy's halo and elsewhere in the universe is expected to generate a diffuse flux of gamma rays, potentially observable with next generation satellite-based experiments, such as GLAST. In this article, we study the signatures of dark matter in the angular distribution of this radiation. Pertaining to the extragalactic contribution, we discuss the effect of the motion of the solar system with respect to the cosmological rest frame and anisotropies due to the structure of our local universe. For the gamma ray flux from dark matter in our own Galactic halo, we discuss the effects of the offset position of the solar system, the Compton-Getting effect, the asphericity of the Milky Way halo, and the signatures of nearby substructure. We explore the prospects for the detection of these features by the GLAST satellite and find that, if ~10% or more of the diffuse gamma ray background observed by EGRET is the result of dark matter annihilations, then GLAST should be sensitive to anisotropies down to the 0.1% level. Such precision would be sufficient to detect many, if not all, of the signatures discussed in this paper
IceCube events and decaying dark matter: hints and constraints
In the light of the new IceCube data on the (yet unidentified) astrophysical
neutrino flux in the PeV and sub-PeV range, we present an update on the status
of decaying dark matter interpretation of the events. In particular, we develop
further the angular distribution analysis and discuss the perspectives for
diagnostics. By performing various statistical tests (maximum likelihood,
Kolmogorov-Smirnov and Anderson-Darling tests) we conclude that currently the
data show a mild preference (below the two sigma level) for the angular
distribution expected from dark matter decay vs. the isotropic distribution
foreseen for a conventional astrophysical flux of extragalactic origin. Also,
we briefly develop some general considerations on heavy dark matter model
building and on the compatibility of the expected energy spectrum of decay
products with the IceCube data, as well as with existing bounds from
gamma-rays. Alternatively, assuming that the IceCube data originate from
conventional astrophysical sources, we derive bounds on both decaying and
annihilating dark matter for various final states. The lower limits on heavy
dark matter lifetime improve by up to an order of magnitude with respect to
existing constraints, definitively making these events---even if astrophysical
in origin---an important tool for astroparticle physics studies.Comment: 27 pages, 10 figures; v2: references added, clarifications included,
matches the version published in JCA
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