μ-τ置換対称性の有効性と2ループ量子効果によるニュートリノ質量生成機構

概要

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Bilarge neutrino mixing is shown to arise from μ-τ permutation symmetry of S_2 supplemented by approximate electron number conservation. The S_2 symmetry first ensures the appearance of the bimaximal neutrino mixing with |U_<e3>|=1. and, then, its tiny violation leads to the bilarge neutrino mixing. Another tiny violation of the electron number conservation yields the appearance of the observed mass hierarchy of Δm^2_〓≪Δm^2_<atm>. An explicit model that realizes this scenario is given by an SU(3)_L×U(1)_N model with two-loop radiative mechanism for neutrino masses. Heavy leptons are contained in lepton triplets and their two-loop radiative effect generate the bimaximal structure while charged-lepton's two-loop radiative effects, which break S_2, finally generate the bilarge structure together with |U_<e3>|≪1. The absence of one-loop radiative effects is ensured by the presence of a Z_8 discrete symmetry that simultaneously forbids the appearance of dangerous flavor-changing neutral current interactions due to Higgs exchanges especially for quarks.
東海大学の論文
2005-03-30