Tri-bimaximal neutrino mixing from A4 and θ13∼θC

It is a common believe that, if the tri-bimaximal mixing (TBM) pattern is explained by vacuum alignment in an A4 model, only a very small reactor angle, say θ13∼O(λC2) being λC≡θC the Cabibbo angle, can be accommodated. This statement is based on the assumption that all the flavon fields acquire VEVs at a very similar scale and the departures from exact TBM arise at the same perturbation level. From the experimental point of view, however, a relatively large value θ13∼O(λC) is not yet excluded by present data. In this paper, we propose a seesaw A4 model in which the previous assumption can naturally be evaded. The aim is to describe a θ13∼O(λC) without conflicting with the TBM prediction for θ12 which is rather close to the observed value (at λC2 level). In our model the deviation of the atmospherical angle from maximal is subject to the sum-rule: sin2θ23≈1/2+2/2cosδsinθ13 which is a next-to-leading order prediction of our model.