321 research outputs found
Model-independent dark matter annihilation bound from the diffuse gamma ray flux
An upper limit on the total annihilation cross section of dark matter (DM)
has recently been derived from the observed atmospheric neutrino background. We
show that comparable bounds are obtained for DM masses around the TeV scale by
observations of the diffuse gamma-ray flux by EGRET, because electroweak
bremsstrahlung leads to non-negligible electromagnetic branching ratios, even
if DM particles only couple to neutrinos at tree level. A better mapping and
the partial resolution of the diffuse gamma-ray background into astrophysical
sources by the GLAST satellite will improve this bound in the near future.Comment: 4 pages revtex, 2 figures; minor changes, references added,
conclusions unchanged; Matches published versio
Standard and non-standard primordial neutrinos
The standard cosmological model predicts the existence of a cosmic neutrino
background with a present density of about 110 cm^{-3} per flavour, which
affects big-bang nucleosynthesis, cosmic microwave background anisotropies, and
the evolution of large scale structures. We report on a precision calculation
of the cosmic neutrino background properties including the modification
introduced by neutrino oscillations. The role of a possible
neutrino-antineutrino asymmetry and the impact of non-standard
neutrino-electron interactions on the relic neutrinos are also briefly
discussed.Comment: 4 pages, no figures. Contribution to the proceedings of SNOW 2006,
Stockholm, May 2-6, 2006. Typos corrected, updated reference
Neutrinos and Cosmology: an update
We review the current cosmological status of neutrinos, with particular
emphasis on their effects on Big Bang Nucleosynthesis, Large Scale Structure of
the universe and Cosmic Microwave Background Radiation measurements.Comment: 4 pages, 1 figure, to appear in the proceedings of IFAE, Catania 200
Measuring the 13-mixing angle and the CP phase with neutrino telescopes
The observed excess of high-energy cosmic rays from the Galactic plane in the
energy range \sim 10^18 eV may be naturally explained by neutron primaries
generated in the photo-dissociation of heavy nuclei. In this scenario, neutrons
with lower energy decay before reaching the Earth and produce a detectable flux
in a 1 km^3 neutrino telescope. The initial flavor composition of these
neutrinos, \phi(\bar\nu_e):\phi(\bar\nu_\mu):\phi(\bar\nu_\tau)=1:0:0, offers
the opportunity to perform a combined \bar\nu_\mu/\bar\nu_\tau appearance and
\bar\nu_e disappearance experiment. The observable ratio
\phi(\bar\nu_\mu)/\phi(\bar\nu_e+\bar\nu_\tau) of fluxes arriving on Earth
depends appreciably on the 13-mixing angle \theta_13 and the leptonic CP phase
\delta_CP, opening thus a new experimental avenue to measure these two
quantities.Comment: 4 pages, 2 eps figures. Enlarged discussion, references added.
Matches version to appear in PR
The Galactic magnetic field as spectrograph for ultra-high energy cosmic rays
We study the influence of the regular component of the Galactic magnetic
field (GMF) on the arrival directions of ultra-high energy cosmic rays
(UHECRs). We find that, if the angular resolution of current experiments has to
be fully exploited, deflections in the GMF cannot be neglected even for E=10^20
eV protons, especially for trajectories along the Galactic plane or crossing
the Galactic center region. On the other hand, the GMF could be used as a
spectrograph to discriminate among different source models and/or primaries of
UHECRs, if its structure would be known with sufficient precision. We compare
several GMF models introduced in the literature and discuss for the example of
the AGASA data set how the significance of small-scale clustering or
correlations with given astrophysical sources are affected by the GMF. We point
out that the non-uniform exposure to the extragalactic sky induced by the GMF
should be taken into account estimating the significance of potential
(auto-)correlation signals.Comment: 11 pages, 8 figures; minor corrections, enlarged discussion, contains
an extended review on Galactic magnetic field compared to published version,
to appear in Astroparticle Physic
Theoretical uncertainties in extracting cosmic-ray diffusion parameters: the boron-to-carbon ratio
PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly
reduced statistical uncertainties in experimental measurements of cosmic-ray
fluxes. In particular, new determinations of traditional diagnostic tools such
as the boron-to-carbon ratio (B/C) are expected to significantly reduce errors
on cosmic-ray diffusion parameters, with important implications for
astroparticle physics, ranging from inferring primary source spectra to
indirect dark matter searches. It is timely to stress, however, that the
conclusions obtained crucially depend on the framework in which the data are
interpreted as well as from some nuclear input parameters. We aim at assessing
the theoretical uncertainties affecting the outcome, with models as simple as
possible while still retaining the key dependencies. We compare different
semi-analytical, two-zone model descriptions of cosmic-ray transport in the
Galaxy. We test for the effect of a primary source contamination in the boron
flux by parametrically altering its flux, as well as for nuclear cross section
uncertainties. Our study on preliminary results from AMS-02 suggests that,
differently for instance from the leptonic case, realistic modelling of the
geometry of the Galaxy and of the source distribution are of minor importance
to correctly reproduce B/C data at high energies and thus, to a large extent,
for the extraction of diffusion parameters. The Ansatz on the lack of primary
injection of boron represents the most serious bias, and requires
multi-messenger studies to be addressed. If this uncertainty could be lifted,
nuclear uncertainties would still represent a serious concern, which degrade
the systematic error on the inferred parameters to the 20% level, or three
times the estimated experimental sensitivity. In order to reduce this, a new
nuclear cross section measurement campaign is probably required.Comment: 14 pages, 11 figures, 4 tables, published in A&
Earth matter effects in supernova neutrinos: Optimal detector locations
A model-independent experimental signature for flavor oscillations in the
neutrino signal from the next Galactic supernova (SN) would be the observation
of Earth matter effects. We calculate the probability for observing a Galactic
SN shadowed by the Earth as a function of the detector's geographic latitude.
This probability depends only mildly on details of the Galactic SN
distribution. A location at the North Pole would be optimal with a shadowing
probability of about 60%, but a far-northern location such as Pyhasalmi in
Finland, the proposed site for a large-volume scintillator detector, is almost
equivalent (58%). We also consider several pairs of detector locations and
calculate the probability that only one of them is shadowed, allowing a
comparison between a shadowed and a direct signal. For the South Pole combined
with Kamioka this probability is almost 75%, for the South Pole combined with
Pyhasalmi it is almost 90%. One particular scenario consists of a large-volume
scintillator detector located in Pyhasalmi to measure the geo-neutrino flux in
a continental location and another such detector in Hawaii to measure it in an
oceanic location. The probability that only one of them is shadowed exceeds 50%
whereas the probability that at least one is shadowed is about 80%. We provide
an online tool to calculate different shadowing probabilities for the one- and
two-detector cases.Comment: v2: 17 pages, 6 eps figures. Typos removed, matches the published
version. Online tool to calculate the Earth shadowing probabilities available
at http://www.mppmu.mpg.de/supernova/shadowing . High-resolution color
version of fig_2a and fig_2b available at
http://www.mppmu.mpg.de/supernova/shadowing/ma
The footprint of large scale cosmic structure on the ultra-high energy cosmic ray distribution
Current experiments collecting high statistics in ultra-high energy cosmic
rays (UHECRs) are opening a new window on the universe. In this work we discuss
a large scale structure model for the UHECR origin which evaluates the expected
anisotropy in the UHECR arrival distribution starting from a given astronomical
catalogue of the local universe. The model takes into account the main
selection effects in the catalogue and the UHECR propagation effects. By
applying this method to the IRAS PSCz catalogue, we derive the minimum
statistics needed to significatively reject the hypothesis that UHECRs trace
the baryonic distribution in the universe, in particular providing a forecast
for the Auger experiment.Comment: 21 pages, 14 figures. Reference added, minor changes, matches
published versio
Primordial Nucleosynthesis: from precision cosmology to fundamental physics
We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss
the main improvements which have been achieved in the past two decades on the
overall theoretical framework, summarize the impact of new experimental results
on nuclear reaction rates, and critically re-examine the astrophysical
determinations of light nuclei abundances. We report then on how BBN can be
used as a powerful test of new physics, constraining a wide range of ideas and
theoretical models of fundamental interactions beyond the standard model of
strong and electroweak forces and Einstein's general relativity.Comment: 148 pages, 66 figures, revised version accepted by Physics Report
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