Two–mixing Texture for Three Active Neutrinos *

The conjecture that among three massive neutrinos ν1 , ν2 , ν3 there is no direct mixing between ν1 and ν3 leads to a two–mixing texture for three active neutrinos νe , νμ , ντ . This texture, much discussed previously, is neatly consistent with the observed deficits of solar νe’s and atmospheric νμ’s, but (without extra mixing with at least one sterile neutrino νs) predicts no LSND effect for accelerator νμ’s. In this option, the masses m 2 1 < ∼ m2 ≪ m3 are readily estimated. The characteristic feature of the two–mixing neutrino texture that only the close neighbours in the hierarchy of massive neutrinos ν1 , ν2 , ν3 mix significantly may be physically meaningful. Going out from the notion of mixing matrix we construct an intrinsic occupation–number operator whose eigenvalues 0, 1, 2 numerate the three generations of massive neutrinos. Analogical constructions work also for charged leptons as well as for up and down quarks.