It is shown that the results of the Super-Kamiokande atmospheric neutrino
experiment, interpreted in terms of nu_munu_tau flavor transitions, can
probe possible decoherence effects induced by new physics (e.g., by quantum
gravity) with high sensitivity, supplementing current laboratory tests based on
kaon oscillations and on neutron interferometry. By varying the (unknown)
energy dependence of such effects, one can either obtain strong limits on their
amplitude, or use them to find an unconventional solution to the atmospheric nu
anomaly based solely on decoherence.Comment: Title changed; major changes in the text; includes the discussion of
a new solution to the atmosheric neutrino anomaly, based on decoherence; a
second figure and a note have been adde