Neutrino oscillations in the framework of three-generation mixings with mass hierarchy

We have analyzed the results of reactor and accelerator neutrino oscillation experiments in the framework of a general model with mixing of three neutrino fields and a neutrino mass hierarchy that can accommodate the results of the solar neutrino expeiments. It is shown that νμ ⇆ νℓ oscillations with 0.6 ≤ Δm2 ≤ 100 eV2 and amplitude larger than 2 × 10−3 are not compatible with the existing limits on neutrino oscillations if the non-diagonal elements of the mixing matrix |Uℓ3| and |Uμ3| are small. Thus, if the excess of electron events recently observed in the LSND experiment is due to νμ ⇆ νℓ oscillations, the mixing in the lepton sector is basically different from the CKM mixing of quarks. If this type of mixing is realized in nature, the observation of νμ ⇆ νℓ oscillations would not influence νμ ⇆ ντ oscillations that are being searched for in the CHORUS and NOMAD experiments.