Perturbative generation of theta_{13} from tribimaximal neutrino mixing
  Solar and atmospheric neutrino oscillations are consistent with a tribimaximal form of the mixing matrix $U$ of the lepton sector. Exact tribimaximal mixing leads to $\theta_{13}=0$. Recent results from the Daya Bay and RENO experiments have established a non-zero value of $\theta_{13}$. Keeping the leading behaviour of $U$ as tribimaximal we perform a model-independent perturbative calculation to incorporate a non-vanishing $\theta_{13}$. We identify the nature of the perturbation matrix and consider the possibility of the solar neutrino splitting also resulting from it. We calculate up to first order in perturbation theory and evaluate the deviations proportional to $\sin \theta_{13}$ while including CP-nonconservation. Finally, we briefly discuss a gauge model where such an addition to the neutrino mass matrix arises through one-loop effects. 
Biswajoy Brahmachari (Vidyasagar Evening Coll.) and Amitava   Raychaudhuri (Univ. of Calcutta)
hep-ph