After the successful determination of the reactor neutrino mixing angle theta_13 ~ 0.16 eq 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_e^dagger U_ u, where U_e and U_ u result from the diagonalisation of the charged lepton and neutrino mass matrices, and assuming that U_ u 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_ u so that theta_13, theta_23 and the solar neutrino mixing angle theta_12 have values compatible with the current data. Two possible orderings of the 12 and the 23 rotations in U_e, standard and inverse, are considered. The results we obtain depend strongly on the type of ordering. In the case of standard ordering, in particular, the Dirac CP violation phase delta, present in U, is predicted to have a value in a narrow interval around i) delta ~ pi in the BM (or LC) case, ii) delta ~ 3pi/2 or pi/2 in the TBM case, the CP conserving values delta = 0, pi, 2pi being excluded in the TBM case at more than 4sigma. In the addendum we discuss the implications of the latest 2013 data.
The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle theta_13 in the lepton sector. In this paper we show how a large theta_13 can arise from the charged lepton sector alone in the context of a
n SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.
