Abstract: |
After the successful determination of the reactor neutrino mixing angle \mbox{$\theta_{13} \cong 0.16 \neq 0$}, a new feature suggested by the current neutrino oscillation data is a sizeable deviation of the atmospheric neutrino mixing angle $\theta_{23}$ from $\pi/4$. Using the fact that the neutrino mixing matrix $U = U^\dagger_{e}U_{\nu}$, where $U_{e}$ and $U_{\nu}$ result from the diagonalisation of the charged lepton and neutrino mass matrices, and assuming that $U_{\nu}$ has a i) bimaximal (BM), ii) tri-bimaximal (TBM) form, or else iii) corresponds to the conservation of the lepton charge $L' = L_e - L_\mu - L_{\tau}$ (LC), we investigate quantitatively what are the minimal forms of $U_e$, in terms of angles and phases it contains, that can provide the requisite corrections to $U_{\nu}$ so that $\theta_{13}$, $\theta_{23}$ and the solar neutrino mixing angle $\theta_{12}$ have values compatible with the current data. In the case of the ``standard'' ordering of the 12 and the 23 rotations in $U_e$, the Dirac CP violation phase $\delta$, present in the PMNS matrix $U$, is predicted to have a value in a narrow interval around i) $\delta \cong \pi$ in the BM (or LC) case, ii) $\delta \cong 3\pi/2$ or $\pi/2$ in the TBM case, the CP conserving values $\delta = 0, \pi, 2\pi$ being excluded in the TBM case at more than $4\sigma$. |