The existence of cosmic rays transcending the Greisen-Zatsepin-Kuzmin (GZK) cutoff appear to be a fact of life. While there is still some controversy regarding the observational data, it appears that opinions converge toward acknowledging the existence of trans-GZK events. Clearly, the issue will be satisfactorily clarified once future detectors, such as OWL, EUSO, the Pierre Auger Observatory,...

Cosmic rays of energies larger than the Greisen–Zatsepin–Kuzmin (GZK) cutoff may be neutrinos if they acquire strong interactions due to a “precocious unification” of forces. A scenario for this to happen is outlined. There is no contradiction with precision measurements carried out at LEP and SLAC. Observable consequences at LHC and future neutrino detectors are discussed. PACS 13.85.T, 13.15,...

The composition of ultra-high energy (UHE) cosmic rays E > 10 eV is still unknown. The observation of UHE photons would extend the observed electromagnetic spectrum to highest energy and open a new channel for multimessenger observations in the universe. Current limits on the photon flux already constrain “exotic” scenarios where a large number of photons is expected by the decay products of su...

Ultra High Energy (UHE) neutrino Astronomy and relic Neutrino masses may play a key role in solving the Ultra High Energy Cosmic Ray (UHECR) puzzle within the Z-Showering model. Tau air-shower originated by UHE neutrino in matter may probe and amplify this expected UHE neutrino Astronomy. The discover of upcoming and horizontal τ air-showers (UPTAUs, HORTAUs), born by UHE, ντ interacting inside...

The flux of cosmic rays beyond the GZK cutoff (∼ 10 20 eV) may be explained through their production by ultra high energy cosmic neutrinos, annihilating on the relic neutrino background, in the vicinity of our galaxy. This process is mediated through the production of a Z boson at resonance, and is generally known as the Z-Burst mechanism. We show that a similar mechanism can also contribute to...