Related papers: Are topological defects responsible for the 300 Ee…
We argue that due to various restrictions cosmic strings and monopole-string networks are not likely to produce the observed flux of ultra-high energy cosmic rays (UHECR). Among the topological defects studied so far, the most promising…
Cosmic ray particles with energies in excess of 10**(20) eV have been detected. The sources as well as the physical mechanism(s) responsible for endowing cosmic ray particles with such enormous energies are unknown. This report gives a…
The clustering of ultra high energy (above 10^20 eV) cosmic rays (UHECR) suggests that they might be emitted by compact sources. Statistical analysis of Dubovsky et al. (Phys. Rev. Lett. 85 (2000) 1154) estimated the source density. We…
Ultra High Energy Cosmic Rays, UHECR, are charged particles with energies between $\sim10^{18}\,{\rm eV}$ and $\sim3\times10^{20}\,{\rm eV}\sim50\,{\rm J}$. They exhibit fundamental physics at energies inaccessible to terrestrial…
We report an estimation of the injected mass composition of ultra-high energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky distribution of UHECR events observed by the…
We present the results of Monte-Carlo simulations of three-dimensional electromagnetic cascade initiated by interactions of the multi-TeV gamma-rays with the cosmological infrared/optical photon background in the intergalactic medium.…
Top-down models of cosmic rays produce more neutrinos than photons and more photons than protons. In these models, we reevaluate the fluxes of neutrinos associated with the highest energy cosmic rays in light of mounting evidence that they…
Motivated by recent measurements of the major components of the cosmic radiation around 10 TeV/nucleon and above, we discuss the phenomenology of a model in which there are two distinct kinds of cosmic ray accelerators in the galaxy.…
Data of Pierre Auger Observatory show a proton-dominated chemical composition of ultrahigh-energy cosmic rays spectrum at (1 - 3) EeV and a steadily heavier composition with energy increasing. In order to explain this feature we assume that…
Propagation of ultra-high energy photons in the galactic and intergalactic space gives rise to cascades comprising thousands of photons. Using Monte Carlo simulations, we investigate the development of such cascades in the solar…
The existence of cosmic rays of energies exceeding 10^20 eV is one of the mysteries of high energy astrophysics. The spectrum and the high energy to which it extends rule out almost all suggested source models. The challenges posed by…
Ultra High Energy Cosmic Rays (UHECR) can be a signal from very early (post-inflationary) Universe. At this cosmological epoch Topological Defects (TD) and long-lived suprheavy (SH) particles are expected to be naturally and effectively…
The current status of origin of Ultra High Energy Cosmic Rays (UHECR) is reviewed, with emphasis given to elementary particle solutions to UHECR problem, namely to Topological Defects and Super-Heavy Dark Matter (SHDM) particles. The relic…
We consider the advantages of and the problems associated with hypotheses to explain the origin of ulthrahigh energy cosmic rays (UHECR: E > 10 EeV) and the "trans GZK" cosmic rays (TGZK: E > 100 EeV), both through "old physics"…
Extremely high energy (up to 10**(22) eV) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from the Big Bang. We perform numerical calculations to show that such cascades could contribute…
The lack of a high energy cutoff in the cosmic ray spectrum together with an apparently isotropic distribution of arrival directions for the highest energy events have strongly constrained most models proposed for the generation of these…
It is likely that ultra-high energy cosmic rays contain a significant component of heavy or intermediate mass nuclei. The propagation of ultra-high energy nuclei through cosmic radiation backgrounds is more complicated than that of protons…
Measurements of proton and nuclear collisions at the Large Hadron Collider at nucleon-nucleon c.m. energies up to $\sqrt{s_{NN}}=$ 13 TeV, have improved our understanding of hadronic interactions at the highest energies reached in…
Understanding the acceleration of Ultra High Energy Cosmic Rays is one of the great challenges of contemporary astrophysics. In this short review, we summarize the general observational constraints on their composition, spectrum and…
The origin of the ultra high energy cosmic rays (UHECR) with energies above E > 1017eV, is still unknown. The discovery of their sources will reveal the engines of the most energetic astrophysical accelerators in the universe. This is a…