Neutrino Oscillations Induced by Two-loop Radiative Effects

Phenomena of neutrino oscillations are discussed on the basis of two-loop radiative neutrino mechanism. Neutrino mixings are experimentally suggested to be maximal in both atmospheric and solar neutrino oscillations. By using Le −Lμ −Lτ (≡ L )-conservation, which, however, only ensures the maximal solar neutrino mixing, we find that two-loop radiative mechanism dynamically generates the maximal atmospheric neutrino mixing and that the estimate of ∆m2⊙/∆m 2 atm ∼ ǫme/mτ explains ∆m2⊙/∆m 2 atm ≪ 1 because of me/mτ ≪ 1, where ǫ measures the breaking of the L -conservation. Together with ∆m2atm ≈ 3 × 10 −3 eV, this estimate yields ∆m2⊙ ∼ 10 −7 eV for ǫ ∼ 0.1, which corresponds to the LOW solution to the solar neutrino problem. Neutrino mass scale is given by (16π)memτ/M (M ∼ 1 TeV), which is of order 0.01 eV.