  Flavor changing (FC) neutrino-matter interactions can account for the
zenith-angle dependent deficit of atmospheric neutrinos observed in the
SuperKamiokande experiment, without directly invoking neither neutrino mass,
nor mixing. We find that FC $\nu_\mu$-matter interactions provide a good fit to
the observed zenith angle distributions, comparable in quality to the neutrino
oscillation hypothesis. The required FC interactions arise naturally in many
attractive extensions of the Standard Model.

High Energy Physics - Phenomenology