1,095 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
Lorentz Violation for Photons and Ultra-High Energy Cosmic Rays
Lorentz symmetry breaking at very high energies may lead to photon dispersion
relations of the form omega^2=k^2+xi_n k^2(k/M_Pl)^n with new terms suppressed
by a power n of the Planck mass M_Pl. We show that first and second order terms
of size xi_1 > 10^(-14) and xi_2 < -10^(-6), respectively, would lead to a
photon component in cosmic rays above 10^(19) eV that should already have been
detected, if corresponding terms for electrons and positrons are significantly
smaller. This suggests that Lorentz invariance breakings suppressed up to
second order in the Planck scale are unlikely to be phenomenologically viable
for photons.Comment: 4 revtex pages, 3 postscript figures included, version published in
PR
Neutrino Oscillations, Lorentz/CPT Violation, and Dark Energy
If dark energy (DE) couples to neutrinos, then there may be apparent
violations of Lorentz/CPT invariance in neutrino oscillations. The DE-induced
Lorentz/CPT violation takes a specific form that introduces neutrino
oscillations that are energy independent, differ for particles and
antiparticles, and can lead to novel effects for neutrinos propagating through
matter. We show that ultra-high-energy neutrinos may provide one avenue to seek
this type of Lorentz/CPT violation in \nu_\mu-\nu_\tau oscillations, improving
the current sensitivity to such effects by seven orders of magnitude.
Lorentz/CPT violation in electron-neutrino oscillations may be probed with the
zenith-angle dependence for high-energy atmospheric neutrinos. The ``smoking
gun,'' for DE-neutrino coupling would, however, be a dependence of neutrino
oscillations on the direction of the neutrino momentum relative to our peculiar
velocity with respect to the CMB rest frame. While the amplitude of this
directional dependence is expected to be small, it may nevertheless be worth
seeking in current data and may be a target for future neutrino experiments.Comment: 9 pages, 3 figure
Constraints on the origin of the ultra-high energy cosmic-rays using cosmic diffuse neutrino flux limits: An analytical approach
Astrophysical neutrinos are expected to be produced in the interactions of
ultra-high energy cosmic-rays with surrounding photons. The fluxes of the
astrophysical neutrinos are highly dependent on the characteristics of the
cosmic-ray sources, such as their cosmological distributions. We study possible
constraints on the properties of cosmic-ray sources in a model-independent way
using experimentally obtained diffuse neutrino flux above 100 PeV. The
semi-analytic formula is derived to estimate the cosmogenic neutrino fluxes as
functions of source evolution parameter and source extension in redshift. The
obtained formula converts the upper-limits on the neutrino fluxes into the
constraints on the cosmic-ray sources. It is found that the recently obtained
upper-limit on the cosmogenic neutrinos by IceCube constrains the scenarios
with strongly evolving ultra-high energy cosmic-ray sources, and the future
limits from an 1 km^3 scale detector are able to further constrain the
ultra-high energy cosmic-rays sources with evolutions comparable to the cosmic
star formation rate.Comment: 9 pages, 3 figures and 1 table. Accepted by Phys. Rev.
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
A Bayesian Approach to Comparing Cosmic Ray Energy Spectra
A common problem in ultra-high energy cosmic ray physics is the comparison of
energy spectra. The question is whether the spectra from two experiments or two
regions of the sky agree within their statistical and systematic uncertainties.
We develop a method to directly compare energy spectra for ultra-high energy
cosmic rays from two different regions of the sky in the same experiment
without reliance on agreement with a theoretical model of the energy spectra.
The consistency between the two spectra is expressed in terms of a Bayes
factor, defined here as the ratio of the likelihood of the two-parent source
hypothesis to the likelihood of the one-parent source hypothesis. Unlike other
methods, for example chi^2 tests, the Bayes factor allows for the calculation
of the posterior odds ratio and correctly accounts for non-Gaussian
uncertainties. The latter is particularly important at the highest energies,
where the number of events is very small.Comment: 22 pages, 10 figures, accepted for publication in Ap
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
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
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
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
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