A Toy model which introduces the different limiting velocities for each particleis discussed: the differentiation of the universal limiting velocity is implemented throgh the coupling with external tensor or vector field, something like Higgs scalar field. GZK cutoff discussion could be altered due to the violation of Lorentz symmetry.

In a large class of string and string inspired models the string excitation and black hole pictures invoked as an explanation of trans-GZK cosmic ray events are equivalent. Single particle inclusive distributions are asymptotically thermal at the Hagedorn temperature. The hadron multiplicities are reminiscent of multiplicities in heavy nucleus initiated interactions.

Fast neutron→mirror neutron (n → n′) oscillations were proposed recently as the explanation of the GZK puzzle. We discuss possible laboratory experiments to search for such oscillations and to improve the present very weak constraints on the value of the n → n′ oscillation probability. PACS: 11.30.Er; 95.35.+d; 14.20.Dh; 28.20.-v

We consider the advantages of and the problems associated with hypotheses to explain the origin of ultrahigh energy cosmic rays (UHECR: E > 10 EeV) and the “trans-GZK” cosmic rays (TGZK: E > 100 EeV) both through (‘old physics” (acceleration in cosmic sources) and “new physics” (new particles, topological defects, fat neutrino cross sections, Lorentz invariance violation).

Observations of cosmic rays with energies above ∼ 4 × 10 GeV have inspired several speculative suggestions concerning their origin. The crucial question is whether or not the spectrum exhibits the expected ‘GZK cutoff’ at this energy — concerning which there are presently contradictory results. If there is indeed a cutoff, then the sources are cosmologically distant and rather exotic in nature....

The paper describes methods used for the detection of cosmic rays with energies above 1018 eV (UHECR, UltraHigh Energy Cosmic Rays). It had been anticipated there would be a cutoff in the energy spectrum of primary cosmic rays around 3·1019 eV induced by their interaction with the 2.7 K primordial photons. This has become known as the GZK cutoff. However, several showers have been detected with...

A main difficulty in the quantization of the gravitational field is the lack of experiments that discriminate among the theories proposed to quantize gravity. Recently we showed that the Standard Model(SM) itself contains tiny Lorentz invariance violation(LIV) terms coming from QG. All terms depend on one arbitrary parameter α that set the scale of QG effects. In this talk we review the LIV for...