1,642 research outputs found
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
Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources
The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show
anisotropies on all scales, from just above the experimental angular resolution
up to medium scales and dipole anisotropies. We find that a global comparison
of the two-point auto-correlation function of the data with the one of
catalogues of potential sources is a powerful diagnostic tool. In particular,
this method is far less sensitive to unknown deflections in magnetic fields
than cross-correlation studies while keeping a strong discrimination power
among source candidates. We illustrate these advantages by considering ordinary
galaxies, gamma ray bursts and active galactic nuclei as possible sources.
Already the sparse publicly available data suggest that the sources of UHECRs
may be a strongly clustered sub-sample of galaxies or of active galactic
nuclei. We present forecasts for various cases of source distributions which
can be checked soon by the Pierre Auger Observatory.Comment: 11 pages, 8 figures, 4 tables; minor changes, matches published
versio
The Nuclear Reactions in Standard BBN
Nowadays, the Cosmic Microwave Background (CMB) anisotropies studies
accurately determine the baryon fraction omega_b, showing an overall and
striking agreement with previous determinations of omega_b obtained from Big
Bang Nucleosynthesis (BBN). However, a deeper comparison of BBN predictions
with the determinations of the primordial light nuclides abundances shows
slight tensions, motivating an effort to further improve the accuracy of
theoretical predictions, as well as to better evaluate systematics in both
observations and nuclear reactions measurements. We present some results of an
important step towards an increasing precision of BBN predictions, namely an
updated and critical review of the nuclear network, and a new protocol to
perform the nuclear data regression.Comment: 4 pp.,4figs. Few typos corrected and updated refs. to match the
version appearing in the proceedings of Conference ``Nuclei in the Cosmos
VIII'', Vancouver, BC, Canada, 19-23 Jul 2004, published in Nucl. Phys.
High Energy Neutrinos with a Mediterranean Neutrino Telescope
The high energy neutrino detection by a km^3 Neutrino Telescope placed in the
Mediterranean sea provides a unique tool to both determine the diffuse
astrophysical neutrino flux and the neutrino-nucleon cross section in the
extreme kinematical region, which could unveil the presence of new physics.
Here is performed a brief analysis of possible NEMO site performances.Comment: 4 pages, 3 figures, Proceedings of the 30th ICRC 200
Disentangling neutrino-nucleon cross section and high energy neutrino flux with a km^3 neutrino telescope
The energy--zenith angular event distribution in a neutrino telescope
provides a unique tool to determine at the same time the neutrino-nucleon cross
section at extreme kinematical regions, and the high energy neutrino flux. By
using a simple parametrization for fluxes and cross sections, we present a
sensitivity analysis for the case of a km^3 neutrino telescope. In particular,
we consider the specific case of an under-water Mediterranean telescope placed
at the NEMO site, although most of our results also apply to an under-ice
detector such as IceCube. We determine the sensitivity to departures from
standard values of the cross sections above 1 PeV which can be probed
independently from an a-priori knowledge of the normalization and energy
dependence of the flux. We also stress that the capability to tag downgoing
neutrino showers in the PeV range against the cosmic ray induced background of
penetrating muons appears to be a crucial requirement to derive meaningful
constraints on the cross section.Comment: 10 pages, 28 figure
Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources
The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show
anisotropies on all scales, from just above the experimental angular resolution
up to medium scales and dipole anisotropies. We find that a global comparison
of the two-point auto-correlation function of the data with the one of
catalogues of potential sources is a powerful diagnostic tool. In particular,
this method is far less sensitive to unknown deflections in magnetic fields
than cross-correlation studies while keeping a strong discrimination power
among source candidates. We illustrate these advantages by considering ordinary
galaxies, gamma ray bursts and active galactic nuclei as possible sources.
Already the sparse publicly available data suggest that the sources of UHECRs
may be a strongly clustered sub-sample of galaxies or of active galactic
nuclei. We present forecasts for various cases of source distributions which
can be checked soon by the Pierre Auger Observatory.Comment: 11 pages, 8 figures, 4 tables; minor changes, matches published
versio
Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic
system as grown by the flux-feeding floating zone technique. A supercurrent
flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances
that are far beyond those expected in a conventional proximity scenario. The
current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted
from the eutectic, exhibit signatures of superconductivity in the bilayered
ruthenate. Detailed microstructural, morphological and compositional analyses
address issues on the concentration and the size of Sr2RuO4 inclusions within
the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous
superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the
Sr2RuO4 inclusions.Comment: Pages 4, figures 3, submitted to Phys. Rev. Let
Sensitivity of a VIRGO pair to stochastic GW backgrounds
The sensitivity of a pair of VIRGO interferometers to gravitational waves
backgrounds (GW) of cosmological origin is analyzed for the cases of maximal
and minimal overlap of the two detectors. The improvements in the detectability
prospects of scale-invariant and non-scale-invariant logarithmic energy spectra
of relic GW are discussed.Comment: 25 pages in RevTex style with 6 figure
On line power spectra identification and whitening for the noise in interferometric gravitational wave detectors
In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
Least Squares ones.Comment: 28 pages, 21 figures, uses iopart.cls accepted for pubblication on
Classical and Quantum Gravit
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