Angular dependence of neutrino flux in KM³ detectors in low scale gravity models

Cubic kilometer neutrino telescopes are capable of probing fundamental questions of ultrahigh energy neutrino interactions. There is currently great interest in neutrino interactions caused by low-scale, extra dimension models. Above 1 PeV the cross section in low scale gravity models rises well above the total standard model cross section. We assess the observability of this effect in the 1–1000 PeV energy range of kilometer-scale detectors, emphasizing several new points that hinge on the enhancement of neutral current cross sections with respect to charged current cross sections. A major point is the importance of “feed-down” regeneration of upward neutrino flux, driven by new-physics neutral current interactions in the flux evolution equations. Feed-down is far from negligible, and it is essential to include its effect. We then find that the angular distribution of events has high discriminating value in separating models. In particular the “up-to-down” ratio between upward- and downward-moving neutrino fluxes is a practical diagnostic tool which can discriminate between models in the near future. The slope of the angular distribution, in the region of maximum detected flux, is also substantially different in low-scale gravity and the standard model. These observables are only weakly dependent on astrophysical flux uncertainties. We conclude that angular distributions can reveal a breakdown of the standard model and probe the new physics beyond, as soon as data become available.