  Massless neutrinos will mix if their couplings to gravity are flavor
dependent, i.e., violate the principle of equivalence. Because the
gravitational interaction grows with neutrino energy, the solar neutrino
problem and the recent atmospheric neutrino data may be simultaneously
explained by violations at the level of 1E-14 to 1E-17 or smaller. This
possibility is severely constrained by present accelerator neutrino experiments
and will be preeminently tested in proposed long baseline accelerator neutrino
experiments.
