757 research outputs found
Minimal Cosmogenic Neutrinos
The observed flux of ultra-high energy (UHE) cosmic rays (CRs) guarantees the
presence of high-energy cosmogenic neutrinos that are produced via
photo-hadronic interactions of CRs propagating through intergalactic space.
This flux of neutrinos doesn't share the many uncertainties associated with the
environment of the yet unknown CR sources. Cosmogenic neutrinos have
nevertheless a strong model dependence associated with the chemical
composition, source distribution or evolution and maximal injection energy of
UHE CRs. We discuss a lower limit on the cosmogenic neutrino spectrum which
depends on the observed UHE CR spectrum and composition and relates directly to
experimentally observable and model-independent quantities. We show explicit
limits for conservative assumptions about the source evolution.Comment: 6 pages, 3 figure
Testing Lorentz Invariance with Ultra High Energy Cosmic Ray Spectrum
The GZK cutoff predicted at the Ultra High Energy Cosmic Ray (UHECR) spectrum
as been observed by the HiRes and Auger experiments. The results put severe
constraints on the effect of Lorentz Invariance Violation(LIV) which has been
introduced to explain the absence of GZK cutoff indicated in the AGASA data.
Assuming homogeneous source distribution with a single power law spectrum, we
calculate the spectrum of UHECRs observed on Earth by taking the processes of
photopion production, pair production and adiabatic energy loss into
account. The effect of LIV is also taken into account in the calculation. By
fitting the HiRes monocular spectra and the Auger combined spectra, we show
that the LIV parameter is constrained to
and respectively, which is well consistent
with strict Lorentz Invariance up to the highest energy.Comment: Accepted for publication in Physical Review D 12 pages, 4 figure
Neutrinos: the Key to UHE Cosmic Rays
Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely
determine both the injection spectrum and the evolution model for UHECR sources
- primarily because interactions during propagation obscure the early Universe
from direct observation. Detection of neutrinos produced in those same
interactions, coupled with UHECR results, would provide a full description of
UHECR source properties.Comment: three pages, three figures. corrected typo
Towards a model of population of astrophysical sources of ultra-high-energy cosmic rays
We construct and discuss a toy model of the population of numerous
non-identical extragalactic sources of ultra-high-energy cosmic rays. In the
model, cosmic-ray particles are accelerated in magnetospheres of supermassive
black holes in galactic nuclei, the key parameter of acceleration being the
black-hole mass. We use astrophysical data on the redshift-dependent black-hole
mass function to describe the population of these cosmic-ray accelerators, from
weak to powerful, and confront the model with cosmic-ray data.Comment: 9 pages, 4 figures, Revtex 4.
Acceptance of fluorescence detectors and its implication in energy spectrum inference at the highest energies
Along the years HiRes and AGASA experiments have explored the fluorescence
and the ground array experimental techniques to measure extensive air showers,
being both essential to investigate the ultra-high energy cosmic rays. However,
such Collaborations have published contradictory energy spectra for energies
above the GZK cut-off. In this article, we investigate the acceptance of
fluorescence telescopes to different primary particles at the highest energies.
Using CORSIKA and CONEX shower simulations without and with the new
pre-showering scheme, which allows photons to interact in the Earth magnetic
field, we estimate the aperture of the HiRes-I telescope for gammas, iron
nuclei and protons primaries as a function of the number of simulated events
and primary energy. We also investigate the possibility that systematic
differences in shower development for hadrons and gammas could mask or distort
vital features of the cosmic ray energy spectrum at energies above the
photo-pion production threshold. The impact of these effects on the true
acceptance of a fluorescence detector is analyzed in the context of top-down
production models
UHECR Particle Spectra from Crypton Decays
We calculate the spectra of ultra-high-energy cosmic rays (UHECRs) in an
explicit top-down model based on the decays of metastable neutral `crypton'
states in a flipped SU(5) string model. For each of the eight specific
10th-order superpotential operators that might dominate crypton decays, we
calculate the spectra of both protons and photons, using a code incorporating
supersymmetric evolution of the injected spectra. For all the decay operators,
the total UHECR spectra are compatible with the available data. Also, the
fractions of photons are compatible with all the published upper limits, but
may be detectable in future experiments.Comment: 9 pages latex, 10 eps figure
Calculation of High Energy Neutrino-Nucleon Cross Sections and Uncertainties Using the MSTW Parton Distribution Functions and Implications for Future Experiments
We present a new calculation of the cross sections for charged current (CC)
and neutral current (NC) and interactions in the neutrino
energy range GeV using the most recent MSTW parton
distribution functions (PDFs), MSTW 2008. We also present the associated
uncertainties propagated from the PDFs, as well as parametrizations of the
cross section central values, their uncertainty bounds, and the inelasticity
distributions for ease of use in Monte Carlo simulations. For the latter we
only provide parametrizations for energies above GeV. Finally, we assess
the feasibility of future neutrino experiments to constrain the cross
section in the ultra-high energy (UHE) regime using a technique that is
independent of the flux spectrum of incident neutrinos. A significant deviation
from the predicted Standard Model cross sections could be an indication of new
physics, such as extra space-time dimensions, and we present expected
constraints on such models as a function of the number of events observed in a
future subterranean neutrino detector.Comment: 20 pages, 13 figures, 5 tables, published in Phys.Rev.D. This version
fixes a typo in Equation 16 of the publication. Also since version v1, the
following changes are in v2 and also in the published version: tables with cs
values, parametrization of the y distribution at low-y improved, the
discussions on likelihood and also earth absorption are expanded, added a
needed minus sign in Eq. 17 of v
Enhanced clustering tendency of Cu-impurities with a number of oxygen vacancies in heavy carbon-loaded TiO2 - the bulk and surface morphologies
The over threshold carbon-loadings (~50 at.%) of initial TiO2-hosts and
posterior Cu-sensitization (~7 at.%) was made using pulsed ion-implantation
technique in sequential mode with 1 hour vacuum-idle cycle between sequential
stages of embedding. The final Cx-TiO2:Cu samples were qualified using XPS
wide-scan elemental analysis, core-levels and valence band mappings. The
results obtained were discussed on the theoretic background employing
DFT-calculations. The combined XPS and DFT analysis allows to establish and
prove the final formula of the synthesized samples as Cx-TiO2:[Cu+][Cu2+] for
the bulk and Cx-TiO2:[Cu+][Cu0] for thin-films. It was demonstrated the in the
mode of heavy carbon-loadings the remaining majority of neutral C-C bonds
(sp3-type) is dominating and only a lack of embedded carbon is fabricating the
O-C=O clusters. No valence base-band width altering was established after
sequential carbon-copper modification of the atomic structure of initial
TiO2-hosts except the dominating majority of Cu 3s states after
Cu-sensitization. The crucial role of neutral carbon low-dimensional impurities
as the precursors for the new phases growth was shown for Cu-sensitized Cx-TiO2
intermediate-state hosts.Comment: 27 pages, 7 figures, accepted to Solid State Science
Cosmological Origin for Cosmic Rays Above eV
The cosmic ray spectrum at , reported by the
Fly's Eye and the AGASA experiments, is shown to be consistent with a
cosmological distribution of sources of protons, with a power law generation
spectrum and energy production rate of
. The two
events measured above are not inconsistent with this model.
Verifying the existence of a ``black-body cutoff'', currently observed with low
significance, would require observation-years with existing
experiments, but only year with the proposed
detectors. For a cosmological source distribution, no anisotropy is expected in
the angular distribution of events with energies up to .Comment: uuencoded gz-compressed postscript file, including 2 figures; To
appear in the October 10 (1995) issue of the Ap. J. Letter
Diagnostic Potential of Cosmic-Neutrino Absorption Spectroscopy
Annihilation of extremely energetic cosmic neutrinos on the relic-neutrino
background can give rise to absorption lines at energies corresponding to
formation of the electroweak gauge boson . The positions of the
absorption dips are set by the masses of the relic neutrinos. Suitably intense
sources of extremely energetic ( -- -eV) cosmic neutrinos
might therefore enable the determination of the absolute neutrino masses and
the flavor composition of the mass eigenstates. Several factors--other than
neutrino mass and composition--distort the absorption lines, however. We
analyze the influence of the time-evolution of the relic-neutrino density and
the consequences of neutrino decay. We consider the sensitivity of the
lineshape to the age and character of extremely energetic neutrino sources, and
to the thermal history of the Universe, reflected in the expansion rate. We
take into account Fermi motion arising from the thermal distribution of the
relic-neutrino gas. We also note the implications of Dirac vs. Majorana relics,
and briefly consider unconventional neutrino histories. We ask what kinds of
external information would enhance the potential of cosmic-neutrino absorption
spectroscopy, and estimate the sensitivity required to make the technique a
reality.Comment: 25 pages, 26 figures (in 46 files), uses RevTe
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