Probing neutrino non–standard interactions with atmospheric neutrino data

We have reconsidered the atmospheric neutrino anomaly in light of the latest data from Super–Kamiokande contained events and from Super–Kamiokande and MACRO up-going muons. We have reanalysed the proposed solution to the atmospheric neutrino anomaly in terms of non–standard neutrino–matter interactions (NSI) as well as the standard νμ → ντ oscillations (OSC). Our statistical analysis shows that a pure NSI mechanism is now ruled out at 99% CL, while the standard νμ → ντ OSC mechanism provides a quite remarkably good description of the anomaly. We therefore study an extended mechanism of neutrino propagation which combines both oscillation and non–standard neutrino–matter interactions, in order to derive limits on flavour–changing (FC) and non–universal (NU) neutrino interactions. We obtain that the off-diagonal flavour–changing neutrino parameter ε is confined to −0.03 < ε < 0.02 at 99% CL, while the diagonal non–universality neutrino parameter ε is bounded to |ε′| < 0.06 at 99% CL. These limits are model independent and they are obtained from pure neutrino–physics processes. The stability of the neutrino oscillation solution to the atmospheric neutrino anomaly against the presence of non–standard neutrino interactions establishes the robustness of the near-maximal atmospheric mixing and massive–neutrino hypothesis. The best agreement with the data is obtained for: ∆m = 2.5× 10 eV, sin(2θ) = 1, ε = −8.6× 10 and ε = 0, although the χ function is quite flat in the ε and ε directions for ε, ε → 0. Typeset using REVTEX