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A.V. Olinto (University of Chicago)
The origin of cosmic rays with energies higher than 1020 eV remains a mystery. Accelerating particles up to these energies is a challenge even for the most energetic astrophysical objects known. While the isotropy in the arrival directions argues for an extra-galactic origin, the photon-pion production off the cosmic background radiation limits the sources of such particles to systems less than 50 Mpc away from us. The combination of large gyroradii, efficient energy losses, and isotropic arrival directions defies most of the proposed astrophysical accelerators as well as the more exotic alternatives. We will review recent observations along with theoretical models for the acceleration and propagation of ultra-high-energy cosmic-rays. We will then discuss the potential of future observatories and the most recent attempts to resolve this astrophysical mystery.
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