Lepton flavour violation in a supersymmetric model with A4 flavour symmetry

We compute the branching ratios for mu -> e gamma, tau -> mu gamma and tau -> e gamma in a supersymmetric model invariant under the flavour symmetry group A(4) x Z(3) x U(1)(FN), in which near tri-bimaximal lepton mixing is naturally predicted. At leading order in the small symmetry breaking parameter u, which is of the same order as the reactor mixing angle theta(13), we find that the branching ratios generically scale as u(2). Applying the current bound on the branching ratio of mu -> e gamma shows that small values of u or tan beta are preferred in the model for mass parameters m(SUSY) and m(1/2) smaller than 1000 GeV. The bound expected from the on-going MEG experiment will provide a severe constraint on the parameter space of the model either enforcing u approximate to 0.01 and small tan beta or m(SUSY) and to m(1/2) above 1000 GeV. In the special case of universal soft supersymmetry breaking terms in the flavon sector a cancellation takes place in the amplitudes and the branching ratios scale as u(4), allowing for smaller slepton masses. The branching ratios for tau -> mu gamma and tau -> e gamma are predicted to be of the same order as the one for mu -> e gamma, which precludes the possibility of observing these tau decays in the near future. (C) 2010 Elsevier B.V. All rights reserved.