Dark Scalar Doublets and Neutrino Tribimaximal Mixing from A_4 Symmetry
  In the context of A_4 symmetry, neutrino tribimaximal mixing is achieved through the breaking of A_4 to Z_3 (Z_2) in the charged-lepton (neutrino) sector respectively. The implied vacuum misalignment of the (1,1,1) and (1,0,0) directions in A_4 space is a difficult technical problem, and cannot be treated without many auxiliary fields and symmetries (and perhaps extra dimensions). It is pointed out here that an alternative scenario exists with A_4 alone and no redundant fields, if neutrino masses are "scotogenic", i.e. radiatively induced by dark scalar doublets as recently proposed. 
Ernest Ma (UC Riverside)