TeV strings and the neutrino-nucleon cross section at ultrahigh energies

In scenarios with the fundamental unification scale at the TeV one expects string excitations of the standard model fields at accessible energies. We study the neutrino-nucleon cross section in these models. We show that dual ity of the scattering amplitude forces the existence of a tower of massive leptoquarks that mediate the process in the s channel. Using the narrow-wid th approximation we find a sum rule for the production rate of resonances w ith different spin at each mass level. We show that these contributions can increase substantially the standard model neutrino-nucleon cross section, although they seem insufficient to explain the cosmic ray events above the Greisen-Zatsepin-Kuz'min cutoff energy.