Pseudo Dirac scenario for neutrino oscillations

We argue how the pseudo Dirac scenario for neutrinos leads to rich neutrino oscillation phenomena, including oscillation inside each generation. The pseudo Dirac scenario is generalized by incorporating generation mixings and formulas for the various neutrino oscillations are derived. As an application we compare the formulas with the corresponding data. We find that the observed pattern of mixings, such as almost maximal mixing in the atmospheric neutrino oscillation, is naturally explained in the generalized pseudo Dirac scenario with small generation mixings. We, however, also point out that there remain some problems to be settled for this scenario to be viable. The possible theoretical framework to realize the pseudo Dirac scenario is also briefly commented on.