Quantum-gravity phenomenology with gamma rays and UHE cosmic rays

In recent years several ideas for experimental searches of effects induced by quantum properties of space-time have been discussed. Some of these ideas concern the role in quantum spacetime of the ordinary Lorentz symmetry of classical flat spacetime. Deviations from ordinary (classical) Lorentz symmetry are now believed to be rather natural in non-commutative space-times, models based on String Theory and models based on Loop Quantum Gravity. Observations of gamma rays and ultra-high-energy cosmic rays could play a key role in the development of this research programme. Invited lecture given at the “International School of Space Science: 2001 course on Astroparticle and Gamma-ray physics in space”, L’Aquila, Italy, August 30–September 7, 2001. To appear in the proceedings.