Supersymmetric A₄ X Z₃ and A₄ Realizations of Neutrino Tribimaximal Mixing Without and With Corrections

In an improved application of the tetrahedral symmetry A_4 first introduced by Ma and Rajasekaran, supplemented by the discrete symmetry Z_3 as well as supersymmetry, a two-parameter form of the neutrino mass matrix is derived which exhibits the tribimaximal mixing of Harrison, Perkins, and Scott. This form is the same one obtained previously by Altarelli and Feruglio, and the inverse of that obtained by Babu and He. If only A_4 is used, then corrections appear, making tan^2(theta_{12}) differenet from 0.5, without changing significantly sin^2(2 theta_{23}) from one or theta_{13} from zero.