Atmospheric neutrinos as probes of neutrino-matter interactions

Neutrino oscillation experiments provide a unique tool for probing neutrino-matter interactions, especially those involving the tau neutrino. We describe the sensitivity of the present atmospheric neutrino data to these interactions in the framework of a three-flavor analysis. Compared to the two-flavor nu_mu-nu_tau analyses, we find qualitatively new features, in particular, that large non-standard interactions, comparable in strength to those in the Standard Model, can be consistent with the data. The existence of such interactions could imply a smaller value of the neutrino mixing angle and larger value of the mass-squared splitting than in the case of standard interactions only. This and other effects of non-standard interactions may be tested in the next several years by MINOS, KamLAND and solar neutrino experiments.