  We consider non-renormalizable 1/M_X interaction terms as a perturbation of
the conventional neutrino mass matrix. Particular attention is given to the
gravitational interaction with M_X=M_Pl. We find that for the degenerate
neutrino mass spectrum, the considered perturbation generates a non-zero U(e3)
which is within reach of the high performance neutrino factories and just on
the borderline to be of interest for supernova physics. For the hierarchical
mass spectrum this effect is small. For 1/M_X interaction terms with M_X about
the GUT scale, a detectable U(e3) term is induced for the hierarchical mass
spectra also. Numerical estimates are given for all the above mentioned cases
and renormalization effects are considered.
