  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.
