TeV strings and ultrahigh-energy cosmic rays

Presented at the XXV International School of Theoretical Physics "Particles and Astrophysics - Standar Models and Beyond", Ustron, Poland, september 10-16, 2001.The origin and nature of ultrahigh-energy cosmic ray events, above the Greisen–Zatsepin–Kuzmin (GZK) cutoff energy, constitute a long-standing, unsolved mystery. Neutrinos are proposed candidates but their standard interactions with matter are too weak. In the context of a TeV-scale string theory, motivated by possible extra space dimensions, the neutrino–nucleon scattering is examined. Resonant string contributions increase substantially the standard model neutrino-nucleon cross section. Although they seem insufficient to explain the trans-GZK cosmic ray events, their effects might be detected in next experiments.Work supported by MCYT, Junta de Andalucía and the European Union under contracts FPA2000-1558, FQM101 and HPRN-CT-2000-00149, respectively