219 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
A phenomenological model of the muon density profile on the ground of very inclined air showers
Ultra-high energy cosmic rays generate extensive air showers in Earth's
atmosphere. A standard approach to reconstruct the energy of an ultra-high
energy cosmic rays is to sample the lateral profile of the particle density on
the ground of the air shower with an array of surface detectors. For cosmic
rays with large inclinations, this reconstruction is based on a model of the
lateral profile of the muon density observed on the ground, which is fitted to
the observed muon densities in individual surface detectors. The best models
for this task are derived from detailed Monte-Carlo simulations of the air
shower development. We present a phenomenological parametrization scheme which
allows to derive a model of the average lateral profile of the muon density
directly from a fit to a set of individual Monte-Carlo simulated air showers.
The model reproduces the detailed simulations with a high precision. As an
example, we generate a muon density model which is valid in the energy range
1e18 eV < E < 1e20 eV and the zenith angle range 60 deg < theta < 90 deg. We
will further demonstrate a way to speed up the simulation of such muon profiles
by three orders of magnitude, if only the muons in the shower are of interest.Comment: Corresponding author: Hans Dembinsk
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
Estimates of multipolar coefficients to search for cosmic ray anisotropies with non-uniform or partial sky coverage
We study the possibility to extract the multipolar moments of an underlying
distribution from a set of cosmic rays observed with non-uniform or even
partial sky coverage. We show that if the degree is assumed to be upper bounded
by , each multipolar moment can be recovered whatever the coverage, but with
a variance increasing exponentially with the bound if the coverage is zero
somewhere. Despite this limitation, we show the possibility to test predictions
of a model without any assumption on by building an estimate of the
covariance matrix seen through the exposure function.Comment: 20 pages, 8 figure
Observational constraints on cosmic-ray escape from ultra-high energy accelerators
The energy spectrum and mass composition of ultra-high energy cosmic rays inferred at the Pierre Auger Observatory are used to derive a benchmark scenario for the emission mechanisms at play in extragalactic accelerators as well as for their energetics and for the abundances of elements in their environments. Assuming a distribution of sources following the density of stellar mass, the gradual increase of the cosmic ray mass number observed on Earth from â2\:EeV up to the highest energies is shown to call for nuclei accelerated up to an energy proportional to their electric charge and emitted with a hard spectral index. In addition, the inferred flux of protons down to â0.6\:EeV is shown to require for this population a spectral index significantly softer than that of heavier nuclei. This is consistent with in-source interactions that shape the energy production rate of injected charged nuclei differently from that of the secondary neutrons escaping from the confinement zone. Together with the inferred abundances of nuclei, these results provide constraints on the radiation levels in the source environments. Within this scenario, an additional component that falls off steeply with increasing energy up to the ankle feature is necessary to make up the all-particle flux in the sub-ankle energy range
Observational constraints on cosmic-ray escape from ultra-high energy accelerators
The energy spectrum and mass composition of ultra-high energy cosmic rays inferred at the Pierre Auger Observatory are used to derive a benchmark scenario for the emission mechanisms at play in extragalactic accelerators as well as for their energetics and for the abundances of elements in their environments. Assuming a distribution of sources following the density of stellar mass, the gradual increase of the cosmic ray mass number observed on Earth from â2 EeV up to the highest energies is shown to call for nuclei accelerated up to an energy proportional to their electric charge and emitted with a hard spectral index. In addition, the inferred flux of protons down to â0.6 EeV is shown to require for this population a spectral index significantly softer than that of heavier nuclei. This is consistent with in-source interactions that shape the energy production rate of injected charged nuclei differently from that of the secondary neutrons escaping from the confinement zone. Together with the inferred abundances of nuclei, these results provide constraints on the radiation levels in the source environments. Within this scenario, an additional component that falls off steeply with increasing energy up to the ankle feature is necessary to make up the all-particle flux in the sub-ankle energy range
Observational Constraints on Cosmic-Ray Escape from Ultrahigh-energy Accelerators
Interactions of ultra-high energy cosmic rays (UHECRs) accelerated in specific astrophysical environments have been shown to shape the energy production rate of nuclei differently from that of the secondary neutrons escaping from the confinement zone. Here, we aim at testing a generic scenario of in-source interactions through phenomenological modeling of the flux and composition of UHECRs. We fit a model in which nucleons and nuclei follow different particle energy distributions to the all-particle energy spectrum and proton spectrum below the ankle energy and distributions of maximum shower depths above this energy, as inferred at the Pierre Auger Observatory. We obtain that the data can be reproduced using a spatial distribution of sources that follows the density of extragalactic matter on both local and large scales, providing hence a realistic set of constraints for the emission mechanisms in cosmic accelerators, for their energetics, and for the abundances of elements at escape from their environments. While the quasi monoelemental increase of the cosmic-ray mass number observed on Earth from â2 EeV up to the highest energies calls for nuclei accelerated with a hard spectral index, the inferred flux of protons down to â0.6 EeV is shown to require for this population a spectral index significantly softer than that generally obtained up to now. We demonstrate that modeling UHECR data across the ankle substantiates the conjecture of in-source interactions in a robust statistical framework, although pushing the mechanism to the extreme
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