The primary protons and the atmospheric neutrino fluxes

The predictions of the atmospheric nu event rates are affected by significant uncertainties, however the evidence for the `disappearance' of nu_mu's and antinu_mu's obtained by SK and other underground detectors is robust and cannot be accounted in the framework of the minimum standard model without assuming very large ad hoc experimental systematic effects. The existence of `new physics' beyond the standard model is therefore close to be established; neutrino oscillations provide a very good fit to all data. The theoretical uncertainties do have an important role in the detailed interpretation of the data, and in the estimate of oscillation parameters.