Current neutrino data are consistent with the so-called tribimaximal mixing scenario, which predicts sin(2) theta(12) = 1/3, zero U-e3 and maximal theta(23). This implies a special form of the neutrino mass matrix. Introducing small breaking terms in this mass matrix generates deviations from the tribimaximal scheme and leads to testable correlations between the parameters. They depend on where the perturbation is located in the mass matrix. A special case of such perturbations are radiative corrections. Alternative deviations from tribimaximal mixing may stem from contributions of the charged lepton sector. If there is quark-lepton unification and it is the CKM matrix which corrects the tribimaximal mixing scheme, then almost maximal CP violation and sizable deviation from zero U-e3 are implied. (c) 2005 Elsevier B.V. All rights reserved.
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