Dr Armando Di Matteo (INFN L'Aquila)Dr Aurelio Grillo (LNGS INFN)
Ultra High Energy Cosmic Rays experimental data are now of very good statistical significance even in the region of the expected GZK feature. The identification of their sources requires sophisticate analysis of their propagation in the extra galactic space. When looking at the details of this propagation some unforeseen features emerge. I will discuss some of these "surprises".