Using cosmic neutrinos to search for nonperturbative physics at the Pierre Auger Observatory

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The Pierre Auger (cosmic ray) Observatory provides a laboratory for studying fundamental physics at energies far beyond those available at colliders. The Observatory is sensitive not only to hadrons and photons but can in principle detect ultrahigh energy neutrinos in the cosmic radiation. Interestingly, it may be possible to uncover new physics by analyzing characteristics of the neutrino flux at the Earth. By comparing the rate for quasihorizontal, deeply penetrating air showers triggered by all types of neutrinos with the rate for slightly up-going showers generated by Earth-skimming tau neutrinos, we determine the ratio of events which would need to be detected in order to signal the existence of new nonperturbative interactions beyond the TeV scale in which the final state energy is dominated by the hadronic component. We use detailed Monte Carlo simulations to calculate the effects of interactions in the Earth and in the atmosphere. We find that observation of 1 Earth skimming and 10 quasihorizontal events would exclude the standard model at the 99% confidence level. If new nonperturbative physics exists, a decade or so would be required to find it in the most optimistic case of a neutrino flux at the Waxman-Bahcall level and a neutrino-nucleon cross section an order of magnitude above the standard model prediction.