Space-time fluctuations and ultra-high energy cosmic ray interactions

The intimate geometry of space—time is expected to suffer stochastic fluctuations as a result of quantum gravitational effects. These fluctuations may induce observable consequences on the propagation of high energy particles over large distances, so that the strength and the characteristics of these fluctuations may be constrained, mainly in the range of energies of interest for cosmic ray physics. While invoked as a possible explanation for the detection of the puzzling cosmic rays with energies in excess of the threshold for photopion production (the so-called super-Greisen Zatsepin— Kuzmin particles), we demonstrate here that lower energy observations may provide strong constraints on the role of a fluctuating space—time structure.