Ultra High Energy Cosmic Rays

We experimentally investigated the SPECT recovery of I-131 activity in multiple spheres located simultaneously at different locations within a cylindrical phantom that had an elliptical cross section. The sphere volumes ranged from 209 cc down to 4.2 cc. A Prism 3000 camera and two types of parallel-hexagonal-hole collimation were employed: high energy (HE) and ultra high energy (UHE). Using appropriately-different 3D models of the point source response function for the two types of collimation, approximately the same recovery of activity could be achieved with either collimation by 3D OSEM reconstruction. The recovery coefficient was greater with no background activity in the phantom by 0.10, on average, compared to that with background. In the HE collimation case, the activity recovery was considerably better for all volumes using 3D OSEM reconstruction than it had been in the past using 1D SAGE reconstruction. Recovery-coefficient-based correction in a simulated patient case involving spherical tumours moderately improved the activity estimates (average error reduced from 14% to 9% for UHE collimation, and from 15% to 11% for HE collimation). For a test case with HE collimation, increasing the projection-image sampling density while decreasing the image voxel size increased the recovery coefficient by 0.075 on average, and, if used in a full set of calibration measurements of recovery coefficient versus volume, might lead to further improvement in accuracy for the patient case.

One of the most spectacular scientific breakthroughs in past decades was using measurements of the fluctuations in the cosmic microwave background (CMB) to test precisely our understanding of the history and composition of the Universe. This report presents a roadmap for leading CMB research to its logical next step, using precision polarization measurements to learn about ultra-high-energy physics and the

Too independent to be in a wife’s frame, besides gender they have in the little which is consort-like...They are individualistic in nature, yet their identity better reveals as a group...The broad meaning of the term ‘Mahavidya’ is ‘great knowledge’. In its wider sense, the term might be taken to mean complete, supreme, absolute, or ultimate knowledge...Ten mantras are ten manifestations of the deity – the Divine Female...As regards the origin of Mahavidyas, the tradition has five myths in prevalence...Frightened Shiva tried to flee from one direction to another but a burst of laughter obstructed him on every side and dismayed and frightened he submitted. To further ensure that he did not slip the woman, obviously, Sati’s transform, filled all directions around him with ten different forms...

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The higher frequency of energy in our atmosphere is referred to as cosmic energy. It appears as a lovely stream of light. The same way that the energy generated by the sun or the moon has an impact on our daily life, cosmic energy has an impact on humans. We can direct this energy to travel through us or send it out into whatever we want with the intention of having a beneficial effect on that object.

The cosmic rays ionize enough the atmosphere to be questioned as possible triggers of the thunderstorms. A mechanism proposed by A. Gurevich and his collaborators suggest that showers of energetic particles produced by high-energy cosmic rays in the terrestrial atmosphere might provide a conductive path that initiates lightning. Because cosmic-ray air showers do not produce enough particles for the electrical discharge by themselves, Gurevich postulated that the thunderstorm gave the cosmic-ray shower a boost by increasing the number of energetic electrons through an exotic process called "runaway breakdown". The Monte Carlo transport calculations of the cosmic-ray muons and associated particles (e.g. knock-on electrons and bremsstrahlung photons) in thunderstorm electric fields, using GEANT4 code indicate that the production of energetic electrons by cosmic ray muons plays an important role in the enhancement of electron and photon fluxes in the thunderstorm electric fields. The Aragats Space Environment Center (ASEC) facilities allow measurements of the charged particles energy from 5 up to 120 MeV. In May − June 2008 we detect short count rate enhancements of low energy charged component of secondary cosmic rays. In the same time there were no peaks in time series of high energy muons. We present first attempt to calculate the energy spectra of the detected additional charged particles, possibly runaway electrons connected with thunderstorm activity.

The CMS/TOTEM and ATLAS collaborations carry out a program of forward physics with several near-beam detectors extending their coverage to high pseudorapidities. This instrumentation includes calorimeters (CASTOR and ZDC), tracking devices (TOTEM T1 and T2), proton taggers (Roman Pots and FP420), and instrumentation dedicated to luminosity monitoring and normalisation. A rich physics program is accessible, including soft QCD interactions, Diffraction, photon-induced physics and luminosity measurements. Half of this large value corresponds to very soft physics, including elastic pp collisions. Five experiments, ATLAS, ALICE, CMS/TOTEM and LHCb observe collision final states at the four interaction regions, IR1, IR2, IR5 and IR8, respectively. ATLAS and CMS are general purpose experiments with central detectors with full φ coverage and a pseudorapidity a η coverage reaching 2.5 for tracking systems and 5.0 for calorimetry. The a The pseudorapidity η is defined in terms of the polar angle θ: η = − ln(tan θ/2).

This review summarizes recent developments in the understanding of high-energy cosmic rays. It focuses on galactic and presumably extragalactic particles in the energy range from the knee (10 15 eV) up to the highest energies observed (> 10 20 eV). Emphasis is put on observational results, their interpretation, and the global picture of cosmic rays that has emerged during the last decade.

We present a study of the decay of an intermediate mini black hole at the first impact of a cosmic ray particle with the atmosphere, in the context of D-brane world scenarios with TeV scale gravity and large extra dimensions. We model the decay of the black hole using the semiclassical approximation and include the corrections coming from energy loss into the bulk. Extensive simulations show that mini black hole events are characterized by essentially different multiplicities and wider lateral distributions of the air showers as a function of the energy of the incoming primary, as compared to standard events. Implications for their detection and some open issues on their possible discovery are also briefly addressed.

A recently published article in Science 1 by the Pierre Auger Laboratory, has helped pinpoint the source of ultrahigh energy cosmic rays, which are the most energetic particles known in the universe. The sources found indicate support for the "active galactic nuclei" theory, which is that the ultra-high energy (UHE) cosmic rays come from super massive black holes found at the centers of galaxies. The Pierre Auger Observatory 2 records the extensive air showers through an array of 1,600 particle detectors placed 1.5 km apart in a grid spread across 3000 square kilometers. In light of this latest development the author wishes to discuss extensive air showers.

An upper limit to the flux of Ultra High Energy (UHE) y-rays in the primary cosmic radiation is obtained through the data of the electromagnetic and the muon detectors of the EAS-TOP Extensive Air Shower array (Camp0 Imperatore, National Gran Sasso Laboratories, atmospheric depth 810gcm-*).

Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse γ-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200 • to 260 • and latitude |b| from 22 • to 60 • ) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of γ-ray point sources and inverse Compton scattering are

High Energy Neutrino Astronomy has been revealed by a sudden change in the flavor composition around maximal energies since three years of recording in ice km detector. However these discover didn' t led to any clear promised Neutrino Astronomy land yet. No correlation with hard gamma sources was found. Moreover the astrophysical spectra expected at Fermi value, seem to converge to a softer value, also required to avoid any Glashow resonant neutrino signal. We suggest a main solution within a composite flux ruled by prompt atmospheric neutrinos. Nevertheless the recent discover of twentyone crossing muons at hundreds TeVs had shown a first narrow overlapped doublet and a correlated track with a peculiar hard UHECR event clustering pointing to a well known microjet in bynary precession; these first connections hint for a non negligible astrophysical component making neutrino astronomy anyway already more than a hope.

1] We have developed a real-time system to monitor high-energy cosmic rays for use in space weather forecasting and specification. Neutron monitors and muon detectors are used for our system, making it possible to observe cosmic rays with dual energy range observations. In large solar energetic particle (SEP) events, the ground level enhancement (GLE) can provide the earliest alert for the onset of the SEP event. The loss cone precursor anisotropy predicts the arrival of interplanetary shocks and the associated interplanetary coronal mass ejections (ICMEs), while the occurrence of bidirectional cosmic ray streaming indicates that Earth is within a large ICME. This article describes a set of real-time Web displays that clearly show the appearance of the GLE, loss cone precursor, and other space weather phenomena related to cosmic rays.

Accuracy of 131I tumor quantification after radioimmunotherapy (RIT) was investigated for SPECT imaging with an ultra-high-energy (UHE) collimator designed for imaging 511-keV photons. First, measurements and Monte Carlo simulations were carried out to compare the UHE collimator with a conventionally used, high-energy collimator. On the basis of this comparison, the UHE collimator was selected for this investigation, which was carried out by simulation of spherical tumors in a phantom. Reconstruction was by an expectation-maximization algorithm that included scatter and attenuation correction. Keeping the tumor activity constant, simulations were carried out to assess how volume-of-interest (VOI) counts vary with background activity, radius of rotation (ROR), tumor location, and size. The constant calibration factor for quantification was determined from VOI counts corresponding to a 3.63-cm-radius sphere of known activity. Tight VOIs corresponding to the physical size of the sphere...

This is mainly a brief review of some key achievements in a "hot" area of theoretical and mathematical physics. The principal aim is to outline the basic structures underlying integrable quantum field theory models with infinite-dimensional symmetry groups which display a radically new type of quantum group symmetries. Certain particular aspects are elaborated upon with some detail: integrable systems of Kadomtsev-Petviashvili type and their reductions appearing in matrix models of strings; Hamiltonian approach to Lie-Poisson symmetries; quantum field theory approach to two-dimensional relativistic integrable models with dynamically broken conformal invariance. All field-theoretic models in question are of primary relevance to diverse branches of physics ranging from nonlinear hydrodynamics to string theory of fundamental particle interactions at ultra-high energies.

We reconsider the Standard Model interactions of ultra-high energy neutrinos with matter. The next to leading order QCD corrections are presented for charged-current and neutral-current processes. Contrary to popular expectations, these corrections are found to be quite substantial, especially for very large (anti-) neutrino energies. Hence, they need to be taken into account in any search for new physics effects in high-energy neutrino interactions. In our extrapolation of the parton densities to kinematical regions as yet unexplored directly in terrestrial accelerators, we are guided by double asymptotic scaling in the large Q 2 and small Bjorken x region and to models of saturation in the low Q 2 and low x regime. The sizes of the consequent uncertainties are commented upon. We also briefly discuss some variables which are insensitive to higher order QCD corrections and are hence suitable in any search for new physics. *

If the history of science has taught us anything, it's that persistence and creativity makes the once impossible possible. It has long been thought experimental tests of quantum gravity are impossible. But during the last decade, several different approaches have been proposed that allow us to test, if not the fundamental theory of quantum gravity itself, so at least characteristic features this theory can have. For the first time we can probe experimentally domains in which quantum physics and gravity cohabit, in spite of our failure so far to make a convincing marriage of them on a theoretical level.

We calculate the flux of ultra high energy photons from individual ordinary (i.e. non-superconducting) cosmic strings and compare the results with the sensitivity of current and proposed TeV and EeV telescopes. Our calculations give only upper limits for the gamma ray flux, since the source of the photons, jets from particle production at cusps, may be weakened by back reaction effects. For the usual cosmic

Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope (GMRT), both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events is expected above $10^{20}$ eV for UHECR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds on UHE particle fluxes by magnitudes competitive to both present and future experiments at the very highest energies.

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093 ± 0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59 Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59 Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed.

The BICEP2 collaboration reports a B-mode polarization of the cosmic microwave background (CMB) radiation inconsistent with the null hypothesis at a significance of > 5 σ. This recent and potentially important result is being often interpreted as a signature of primordial gravitational waves from cosmic inflation. However, the arguments supporting such an interpretation are strictly based on standard cosmology and do not take into account possible new phenomena suggested by Planck data such as the existence of a privileged space direction. In particular, inflation is not needed in pre-Big Bang patterns, and the spinorial space-time (SST) introduced in our 1996-97 papers automatically generates a privileged space direction for each comoving observer. In the presence of this privileged space direction, the existence of CMB B-modes is a natural phenomenon and the signal claimed by BICEP2 would not correspond to any kind of inflationary scenario.

In this work we estimate the heavy quark production in the interaction of ultra high energy cosmic rays in the atmosphere, considering that the primary cosmic ray is a proton or a photon. At these energies the saturation momentum Q_{sat}^2 stays above the hard scale \mu_c^2=4m_c^2, implying charm production probing the saturation regime. In particular, we show that the ep HERA data presents a scaling on \tau_c = (Q^2+\mu_c^2)/Q_{sat}^2. We derive our results considering the dipole picture and the Color Glass Condensate formalism, which one shows to be able to describe the heavy quark production in photon-proton and proton-proton collisions. Nuclear effects are considered in computation of cross sections for scattering on air nuclei. Implications on the flux of prompt leptons at the earth are analyzed and a large suppression is predicted.

Ultra-high-energy (UHE) neutrinos , " , and " e at PeV and higher energies may induce air showers whose detectability is amplified millions to billions of times by their secondaries. We considered UHE -N and UHE " e -e interactions underneath mountains as a source of such horizontal amplified air showers. We also consider vertical upward UHE -N interactions (UPTAUs) on Earth's crust, leading to UHE air showers or interactions at the horizon edges (HORTAUs), and their beaming toward high mountain gamma, X-ray, and Cerenkov detectors, and we show their detectability. We notice that such rare upward air showers, UPTAUs and HORTAUs, may even hit nearby balloons or satellites and flash them with short diluted gamma bursts at the edge of the Compton Gamma Ray Observatory detection threshold. We suggest the possibility of identifying these events with recently discovered (BATSE) terrestrial gamma flashes (TGFs), and we argue for their probable UHE -UHE origin. From these data, approximated UHE fluxes and Dm l lower bounds are derived. Known X-ray, gamma, and TeV active Galactic and extragalactic sources have been identified in most TGF arrival directions. Maximal EGRET activity in the Galactic center overlaps with the maximal TGF flux. The UHE cosmic-ray (UHECR) Akino Giant Air Shower Array anisotropy at 10 18 eV also shows possible correlations with TGF events. The unique UHECR triplet in AGASA clustering, pointing toward BL Lac 1ES 0806+524, finds within its error box a corresponding TGF event, BATSE trigger 2444. Finally, a partial TGF Galactic signature, combined with the above correlations, suggests an astrophysical origin of TGF events.

The Pierre Auger Observatory for cosmic rays provides a laboratory for studying fundamental interactions at energies well beyond those available at colliders. In addition to hadrons or photons, Auger is sensitive to ultra-high energy neutrinos in the cosmic radiation and models for new physics can be explored by observing neutrino interactions at center-of-mass energies beyond the TeV scale. By comparing the rate for quasi-horizontal, deeply penetrating air showers triggered by all types of neutrinos with the rate for slightly upgoing showers generated by Earth-skimming tau neutrinos, any deviation of the neutrino-nucleon cross-section from the Standard Model expectation can be constrained. We show that this can test models of lowscale quantum gravity (including processes such as Kaluza-Klein graviton exchange, microscopic black hole production and string resonances), as well as non-perturbative electroweak instanton mediated processes. Moreover, the observed ratios of neutrino flavors would severely constrain the possibility of neutrino decay.

We present a comprehensive report on the experimental details of the Antarctic Impulsive Transient Antenna (ANITA) long-duration balloon payload, including the design philosophy and realization, physics simulations, performance of the instrument during its first Antarctic flight completed in January of 2007, and expectations for the limiting neutrino detection sensitivity.

We discuss theoretical issues and experimental data that brought the ultra high energy cosmic rays in the list of Nature's greatest puzzles. After many years of research we still do not know how astrophysical acceleration processes can reach energies exceeding 10 11 GeV. The main alternative top-down mechanism postulates the existence of super massive X-particles that create a particle spectrum extending down to the observed energy through their decay channels. The propagation of nuclei and photons from their sources to us adds to the puzzle as all particles of these energies interact with the ambient photons, mostly of the microwave background. We also describe briefly the main observational results and give some information on the new experiments that are being built and designed now.

Recent results from the PAMELA satellite indicate the presence of a large flux of positrons (relative to electrons) in the cosmic ray spectrum between approximately 10 and 100 GeV. As annihilating dark matter particles in many models are predicted to contribute to the cosmic ray positron spectrum in this energy range, a great deal of interest has resulted from this observation. Here, we consider pulsars (rapidly spinning, magnetized neutron stars) as an alternative source of this signal. After calculating the contribution to the cosmic ray positron and electron spectra from pulsars, we find that the spectrum observed by PAMELA could plausibly originate from such sources. In particular, a significant contribution is expected from the sum of all mature pulsars throughout the Milky Way, as well as from the most nearby mature pulsars (such as Geminga and B0656+14). The signal from nearby pulsars is expected to generate a small but significant dipole anisotropy in the cosmic ray electron spectrum, potentially providing a method by which the Fermi gamma-ray space telescope would be capable of discriminating between the pulsar and dark matter origins of the observed high energy positrons. PACS numbers: 98.70.Sa;97.60.Gb;95.35.+d;98.70.Sa

This study was designed to elucidate the usefulness of crosstalk correction for dual-isotope simultaneous acquisition (DISA) with 99mTc-tetrofosmin and FDG in estimating myocardial perfusion and viability. Methods: Eighteen patients with coronary artery disease were studied. First, SPECT was performed with a low-energy high-resolution collimator after a single injection of 99mTc-tetrofosmin (single 99mTc-tetrofosmin). Second, PET and DISA with an ultra-high-energy collimator

Cosmic rays are energetic particles from outside the earth's atmosphere. When a high energy cosmic ray hits the atmosphere it triggers a cascade of secondary particles produced in nuclear interactions, an air shower. Up to now the established methods of measuring air showers are detection of the particles that reach the ground level or optical observation of the Cherenkov or ftuorescent light.

We discuss recent observations of high energy cosmic ray positrons and electrons in the context of hadronic interactions in supernova remnants, the suspected accelerators of galactic cosmic rays. Diffusive shock acceleration can harden the energy spectrum of secondary positrons relative to that of the primary protons and electrons and thus explain the rise in the positron fraction observed by PAMELA above 10 GeV. We normalize the hadronic interaction rate by holding pion decay to be responsible for the gamma-rays detected by HESS from some SNRs. By simulating the spatial and temporal distribution of SNRs in the Galaxy according to their known statistics, we are able to then fit the electron (plus positron) energy spectrum measured by Fermi. It appears that IceCube has good prospects for detecting the hadronic neutrino fluxes expected from nearby SNRs. PACS numbers: 98.70.Sa, 96.50.sb, 98.58.Mj arXiv:0909.4060v2 [astro-ph.HE]

Progress in the field of high-energy cosmic rays is currently limited by the rarity of the most interesting rays striking the Earth. Indeed, the continuation of the field beyond the current generation of observatories may become financially and practically impossible if new ways are not found to achieve remote coverage over large portions of the Earth's surface. We describe the development of an observatory based on such a new technique: the remote sensing via bistatic radar technology of cosmic ray induced extensive air showers. We build on pilot studies performed by MARIACHI which have demonstrated that air shower radar echoes are detectable, the opportunity afforded by the location of the Northern Hemisphere's largest "conventional" cosmic ray observatory (The Telescope Array) in radio-quiet western Utah, and the donation of analog television transmission equipment to this effort by a local television station.

We study the phenomenology of cosmic-rays (CRs) at the galactic/extragalactic transition, focusing on two opposite models for the composition of the extragalactic (EG) component. Model A assumes a mixed source composition, with nuclear abundances similar to that of the low-energy CRs, while model B assumes that EG sources accelerate only protons. We study the limits within which both scenarios can reproduce the observed high-energy CR spectrum and composition. The ankle in model A is interpreted as the GCR/EGCR transition, while in model B it is the pair-production dip. Model A has a source spectrum ∝ E −x with x ∼ 2.2 − 2.3, while model B requires x ∼ 2.6 − 2.7. We compare the predictions of both models with the available data on the energy evolution of the highenergy CR composition using the two main composition-related observables: X max and ln A. We conclude that model A is currently favoured. Uncertainties are discussed and distinctive features of the two models are identified, which should allow one to distinguish between the models in the near future when more precise measurements are available with higher-statistics experiments.

This essay aims to elucidate the role of cosmic rays in the evolutionary process of our Earth. After an initial introduction of the role cosmic rays play in thunderstorms and lightning (and how this affected the plant and human evolution in the past) it will be clarified what cosmic rays are. Afterwards, it is looked into DNA mutation processes and then the reader is directed to take a bit broader point of view. The essay will be concluded with a mythological analogy.

A passive Radio Detector System is proposed for Ultra High Energy Cosmic Rays showers and meteors detection. TV emissions, reflected by ionization clouds produced in such events are acquired producing a clearly detectable profile. A Radio Detection station is operating at BNL recording signal samples from a group of three antennas. An offline analysis, here described, allows for event selection and feature extraction. An event rate consistent with the earth rotation 24 hours periodicity could be found. Auxiliary detectors are being built to validate the results obtained so far.

The problem of ultra high energy charged particle's motion in the cosmic microwave background (CMB) is considered. It is shown that the exact solutions of the relativistic equation for charged particle motion in electromagnetic wave with imposition of initial conditions for coordinate and time of the wave result in an additional energy gain of particle after averaging over initial random phases of the waves. Thus, there is no Greisen-Zatsepin-Kuzmin (GZK) cut-off during propagation of ultra high energy charged particles within the CMB. This situation is similar to the infrared situation in Quantum Electrodynamics: despite the presence of many low-energy photons and multiquantum exchange of energy with the charged particle, the main process -here is the propagation of charged particle of UHECR within the CMB, remains almost unchanged, if we are not interested by delicate distinctions such as small angle deviations of trajectory from the rectilinear line.

The detection of radio pulses emitted in the atmosphere during the air shower development of high-energy primary cosmic rays is the task of the LOPES (LOFAR Prototype Station) project. LOFAR (Low Frequency Array) is a new digital radio interferometer under development using high bandwidth ADCs and fast data processing to filter out most of the interference. By storing the whole waveform information in digital form transient events like air showers can be analyzed even after they have been recorded. To test this technology and to demonstrate its ability to measure air showers a LOPES is set up to operate in conjunction with an existing air shower experiment (KASCADE-Grande). The LOPES antennas are operating in the frequency range of 40-80 MHz. For several air-shower events a coincident and coherent signal has been found and a preliminary analysis has already been performed. The main goal of further investigations is to calibrate the radio signal with help of the observables of the individual air-showers given by KASCADE-Grande.

Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with the highest-energies, which are correlated with the positions of relatively nearby active galactic nuclei (AGN) [Pierre Auger Collaboration, Science 318 ]. The correlation has maximum significance for cosmic rays with energy greater than $6 Â 10 19 eV and AGN at a distance less than $75 Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parameters specified a priori, using an independent data set. The observed correlation is compatible with the hypothesis that cosmic rays with the highest-energies originate from extra-galactic sources close enough so that their flux is not significantly attenuated by interaction with the cosmic background radiation (the Greisen-Zatsepin-Kuz'min effect). The angular scale of the correlation observed is a few degrees, which suggests a predominantly light composition unless the magnetic fields are very weak outside the thin disk of our galaxy. Our present data do not identify AGN as the sources of cosmic rays unambiguously, and other candidate sources which are distributed as nearby AGN are not ruled out. We discuss the prospect of unequivocal identification of individual sources of the highest-energy cosmic rays within a few years of continued operation of the Pierre Auger Observatory.

Advancing QCD toward astroparticle applications generates new challenges for perturbation theory, such as the presence of large evolution scales with sizeable scaling violations involving both the initial and the final state of a collision. Possible applications in the context of Ultra High Energy Cosmic Rays (UHECR) of these effects are discussed. .

A new feature in the spectrum of ultra high energy cosmic rays (UHECR) has been announced in the paper by Berezinsky, Gazizov and Kachelrieß. The ratio of the solution of the exact transport equation to its solution in the continuous energy loss limit shows intriguing features which, according to the Authors, are related to the very nature of the energy loss processes of UHECR: the very sharp second dip predicted at 6.3 × 10 19 eV can be used as an energy calibration point and also as the UHECR mass indicator for big future cosmic ray experiments. In the present paper we would like to advocate that this statement is an overinterpretation. The second dip is a result of an inappropriate approximation used, and thus it cannot help to understand the nature of UHECR in any way.

Abstract: Under current conditions, the cosmic ray spectrum incident on the Earth is dominated by particles with energies< 1 GeV. Astrophysical sources including high energy solar flares, supernovae and gamma ray bursts produce high energy cosmic rays (HECRs) with drastically higher energies. The Earth is likely episodically exposed to a greatly increased HECR flux from such events, some of which lasting thousands to millions of years. The air showers produced by HECRs ionize the atmosphere and produce harmful ...