Neutrino Flavor Mixing in the `Doublet-Singlet Oscillation' Model

Recently, it was pointed out that the solar and atmospheric neutrino deficits can be explained by oscillations between electroweak doublet and singlet neutrinos in the model of Majorana neutrinos. However, since the model includes no flavor mixing, it cannot explain the recent LSND result. We extend the model to include the flavor mixing, and obtain the explanation of the LSND result together with the solar and atmospheric neutrino deficits. The requirement for the neutrinos to be the hot dark matter selects out only the vacuum oscillation solution to the solar neutrino deficit.