Proposed astrophysical test of Lorentz invariance - art. no. 103002

Working in the context of a Lorentz-violating extension of the standard mod el we show that estimates of Lorentz symmetry violation extracted from ultr a-high-energy cosmic rays beyond the Greisen-Kuzmin-Zatsepilk (GZK) cutoff allow for setting bounds on parameters of that extension. Furthermore, we a rgue that a correlated measurement of the difference in the arrival time of gamma-ray photons and neutrinos emitted from active galactic nuclei or gam ma-ray bursts may provide a signature of possible violation of Lorentz symm etry. We have found that this time delay is energy independent; however it has a dependence on the chirality of the particles involved. We also briefl y discuss the known settings where the mechanism for spontaneous Violation of Lorentz symmetry in the context of string/M-theory may take place.