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Observation of Ultra High Energy Cosmic Rays (UHECR) -whose energy exceeds $10^20$eV- is still a puzzle for modern astrophysics. The transfer of more than 16 Joules to a microscopic particle can hardly be achieved, even in the most powerful cosmic accelerators such as AGNs, GRBs or FR-II radio galaxy lobes. Potential sources must also lie within 100 Mpc of the Earth as the interaction length of protons, nuclei or photons is less than 10Mpc. However no visible counterpart of those sources has been observed. Calling upon new physics such as Topological Defect interactions or Super Massive Relic Particle decays is therefore very tempting, but such objects are yet to be proven to exist. Due to the very low flux of UHECR only very large dedicated experiments, such as the Auger observatories, will allow to shed some light on the origin of those cosmic rays. In this quest neutrinos, if they can be detected, are an invaluable messengers of the nature of the sources.
It has been argued that the observations of cosmic particles with energies in excess of $10^8$ TeV represent a puzzle. Its solution requires new astrophysics or new particle physics. We show that the latter is unlikely given that the scale associated
Introducing a simple Galactic wind model patterned after the solar wind we show that back-tracing the orbits of the highest energy cosmic events suggests that they may all come from the Virgo cluster, and so probably from the active radio galaxy M87.
This is a summary of a series of lectures on the current experimental and theoretical status of our understanding of origin and nature of cosmic radiation. Specific focus is put on ultra-high energy cosmic radiation above ~10^17 eV, including seconda
One of several working groups established for this workshop was charged with examining results and methods associated with the UHECR energy spectrum. We summarize the results of our discussions, which include a better understanding of the analysis ch
We explore the joint implications of ultrahigh energy cosmic ray (UHECR) source environments -- constrained by the spectrum and composition of UHECRs -- and the observed high energy astrophysical neutrino spectrum. Acceleration mechanisms producing p