  Although the phenomenon of neutrino oscillations is confirmed in many
experiments, the theoretical explanation of this phenomenon in the literature
is essentially model dependent and is not based on rigorous physical
principles. We propose an approach where the neutrino is treated as a massless
elementary particle in anti-de Sitter (AdS) invariant quantum theory. In
contrast to standard Poincare invariant quantum theory, an AdS analog of the
mass squared changes over time even for elementary particles. Our approach
naturally explains why, in contrast to the neutrino, the electron, muon and tau
lepton do not have flavors changing over time and why the number of solar
neutrinos reaching the Earth is around a third of the number predicted by the
standard solar model.
