The highest energy cosmic rays, above the Greisen–Zatsepin–Kuzmin cut-off of cosmic ray spectrum, may be produced in decays of superheavy long-living X-particles. We conjecture that these particles may be produced naturally in the early Universe from vacuum fluctuations during inflation and may constitute a considerable fraction of Cold Dark Matter. We predict a new cut-off in the UHE cosmic ra...

Ultra High Energy Cosmic Rays (UHECR) can be a signal from very early (post-infationary) Universe. At this cosmological epoch Topological Defects (TD) and long lived superheavy (SH) particles are expected to be naturally and effectively produced. Both of these relics can produce now the particles, such as protons and photons, with energies in a great excess of what is observed in UHECR, E ∼ 10 ...

We develop a perturbative framework with which to discuss departures from exact Lorentz invariance and explore their potentially observable ramifications. Tiny noninvariant terms introduced into the standard model Lagrangian are assumed to be renormalizable (dimension ≤ 4), invariant under SU(3)⊗ SU(2)⊗U(1) gauge transformations, and rotationally and translationally invariant in a preferred fra...

Ultrahigh energy (UHE) extragalactic protons propagating through cosmic microwave radiation (CMB) acquire the spectrum features in the form of the dip, bump (pile-up protons) and the Greisen-Zatsepin-Kuzmin (GZK) cutoff. We have performed the analysis of these features in terms of the modification factor. This analysis is weakly model-dependent, especially in case of the dip. The energy shape o...

We review the basic ideas on the origin of cosmic rays with energy in excess of ∼ 10 eV, in the light of the most recent observational findings. The limited statistics of events detected by the two largest experiments currently operating does not allow as yet to claim the detection of the GZK feature in the cosmic ray spectrum or the lack of it. Although extragalactic point sources seem to be p...

We describe a new experiment to search for neutrinos with energies above 3 × 10 18 eV based on the observation of short duration radio pulses that are emitted from neutrino-initiated cascades. The primary objective of the ANtarctic Impulse Transient Antenna (ANITA) mission is to measure the flux of GreisenZatsepin-Kuzmin (GZK) neutrinos and search for neutrinos from Active Galactic Nuclei (AGN)...

The High Resolution Fly’s Eye (HiRes) Experiment has been in operation in monocular mode since 1997 and in stereo mode since late 1999. The published HiRes monocular spectrum is consistent with the GZK Suppression at 10 eV and observes an ankle structure at 10 eV. The preliminary stereo spectrum is consistent with the monocular spectrum. Various anisotropy studies with both monocular and stereo...

Recently we proposed a new cosmic acceleration mechanism which was based on the wakefields excited by the Alfven shocks in a relativistically flowing plasma. In this paper we include some omitted details, and show that there exists a threshold condition for transparency below which the accelerating particle is collision-free and suffers little energy loss in the plasma medium. The stochastic en...

We discuss four approaches to the determination of absolute neutrino mass. These are the measurement of the zero-neutrino double beta decay rate, of the tritium decay end-point spectrum, of the cosmic ray spectrum above the GZK cutoff, and the cosmological measurement of the power spectrum governing the CMB and large scale structure. The first two approaches are sensitive to the mass eigenstate...