1,087 research outputs found
Comment on "The Lamb Shift and Ultra High Energy Cosmic Rays" and Comment on "Vacuum Polarization Energy Losses of High Energy Cosmic Rays"
The cosmic rays spectrum has been shown to extend well beyond 10^20 eV. With
nearly 20 events observed in the last 40 years, it is now established that
particles with energies near or above 10^21 eV. No nearby astrophysical object
has been shown to correlate with the arrival directions of the highest energy
events, yet the exponential cut-off in the high energy end of the spectrum one
expects to see in the case of far sources is not visible. It was recently
pointed out that the influence of the vacuum of quantum electrodynamics on
particle propagation could explain qualitatively this mystery. This note is a
critic to these ideas.Comment: 4 pages, note on second paper correcte
Searches for Large-Scale Anisotropies of Cosmic Rays: Harmonic Analysis and Shuffling Technique
The measurement of large scale anisotropies in cosmic ray arrival directions
is generally performed through harmonic analyses of the right ascension
distribution as a function of energy. These measurements are challenging due to
the small expected anisotropies and meanwhile the relatively large modulations
of observed counting rates due to experimental effects. In this paper, we
present a procedure based on the shuffling technique to carry out these
measurements, applicable to any cosmic ray detector without any additional
corrections for the observed counting rates.Comment: 22 pages, 10 figures, to appear in Astroparticle Physic
The Small Contribution of Molecular Bremsstrahlung Radiation to the Air-Fluorescence Yield of Cosmic Ray Shower Particles
A small contribution of molecular Bremsstrahlung radiation to the
air-fluorescence yield in the UV range is estimated based on an approach
previously developed in the framework of the radio-detection of showers in the
gigahertz frequency range. First, this approach is shown to provide an estimate
of the main contribution of the fluorescence yield due to the de-excitation of
the C electronic level of nitrogen molecules to the B
one amounting to MeV at
800 hPa pressure and 293 K temperature conditions, which compares well to
previous dedicated works and to experimental results. Then, under the same
pressure and temperature conditions, the fluorescence yield induced by
molecular Bremsstrahlung radiation is found to be
MeV in the wavelength range of
interest for the air-fluorescence detectors used to detect extensive air
showers induced in the atmosphere by ultra-high energy cosmic rays. This means
that out of photons with wavelength between 330 and 400 nm
detected by fluorescence detectors, one of them has been produced by molecular
Bremsstrahlung radiation. Although small, this contribution is not negligible
in regards to the total budget of systematic uncertainties when considering the
absolute energy scale of fluorescence detectors.Comment: 9 pages, 2 figures, accepted for publication in Astropart. Phys.
arXiv admin note: text overlap with arXiv:1601.0055
An Estimate of the Spectral Intensity Expected from the Molecular Bremsstrahlung Radiation in Extensive Air Showers
A detection technique of ultra-high energy cosmic rays, complementary to the
fluorescence technique, would be the use of the molecular Bremsstrahlung
radiation emitted by low-energy electrons left after the passage of the showers
in the atmosphere. The emission mechanism is expected from quasi-elastic
collisions of electrons produced in the shower by the ionisation of the
molecules in the atmosphere. In this article, a detailed calculation of the
spectral intensity of photons at ground level originating from the transitions
between unquantised energy states of free ionisation electrons is presented. In
the absence of absorption of the emitted photons in the plasma, the obtained
spectral intensity is shown to be 5 10^{-26} W m^{-2}Hz^{-1} at 10 km from the
shower core for a vertical shower induced by a proton of 10^{17.5} eV.Comment: 16 pages, 6 figures, accepted in Astroparticle Physics. Compared to
v1 version: 1. Inclusion of ro-vibrational processes. 2. Use of more accurate
ionization potential values and energy distribution of the secondary
electron
Molecular Bremsstrahlung Radiation at GHz Frequencies in Air
A detection technique for ultra-high energy cosmic rays, complementary to the
fluorescence technique, would be the use of the molecular Bremsstrahlung
radiation emitted by low-energy ionization electrons left after the passage of
the showers in the atmosphere. In this article, a detailed estimate of the
spectral intensity of photons at ground level originating from this radiation
is presented. The spectral intensity expected from the passage of the
high-energy electrons of the cascade is also estimated. The absorption of the
photons in the plasma of electrons/neutral molecules is shown to be negligible.
The obtained spectral intensity is shown to be W cm
GHz at 10 km from the shower core for a vertical shower induced by a
proton of eV. In addition, a recent measurement of Bremsstrahlung
radiation in air at gigahertz frequencies from a beam of electrons produced at
95 keV by an electron gun is also discussed and reasonably reproduced by the
model.Comment: 20 pages, 9 figures, figures (2,4,7) improved in v2, accepted by
Phys. Rev.
UHE tau neutrino flux regeneration while skimming the Earth
The detection of Earth-skimming tau neutrinos has turned into a very
promising strategy for the observation of ultra-high energy cosmic neutrinos.
The sensitivity of this channel crucially depends on the parameters of the
propagation of the tau neutrinos through the terrestrial crust, which governs
the flux of emerging tau leptons that can be detected. One of the
characteristics of this propagation is the possibility of regeneration through
multiple conversions, which are often neglected
in the standard picture. In this paper, we solve the transport equations
governing the propagation and compare the flux of emerging tau
leptons obtained allowing regeneration or not. We discuss the validity of the
approximation of neglecting the regeneration using different
scenarios for the neutrino-nucleon cross-sections and the tau energy losses.Comment: 8 pages, 8 figure
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