Abstract :
The observation of ultra high energy cosmic rays above the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy has stirred up considerable interest in particle astrophysics and cosmology. In this paper, I wish to summarize, in a sketchy manner, what we have been trying to do recently in connection with this important problem. We believe that the interpretation of these GZK events already requires a full knowledge of the electroweak physics in the energy range of hundreds of TeVʹs.
