Extremely high energy neutrinos propagating in the atmosphere or in the Earth can originate horizontal or upgoing air-showers, respectively. We calculate the acceptances (event rate/flux) for detecting both types of events by fluorescence detectors, both spacebased as with the EUSO and OWL proposals, and ground-based, as with Auger, HiRes and Telescope Array. We depict them as a function of the...

We briefly review the status of cosmic ray studies between 10 14 eV and the highest observed energies, namely a few times 10 20 eV. Because of the rather low incident fluxes in this energy range, the studies mostly rely on ground based, large aperture detectors reconstructing the cosmic ray's properties through the detection of the air-showers they generate by interacting with the atmosphere. W...

“GZK photons” are produced by extragalactic nucleons through the resonant photoproduction of pions. We present the expected range of the GZK photon fraction of UHECR, assuming a particular UHECR spectrum and primary nucleons, and compare it with the minimal photon fraction predicted by Top-Down models. The Pierre Auger Observatory [1] may prove photon fractions in the Ultra-High Energy Cosmic R...

At very high energies, the Landau-Pomeranchuk-Migdal effect reduces the cross sections for electron bremsstrahlung and photon e + e − pair production. The fractional electron energy loss and pair production cross sections drop as the energy increases. In contrast, the cross sections for photonuclear interactions grow with energy. In solids and liquids, at energies above 10 20 eV, photonuclear r...