Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry

TL;DR

This paper calculates lepton flavor violation rates in a supersymmetric model with A4 symmetry, showing how current and future experiments constrain the model's parameters and predicting similar rates for tau decays.

Contribution

It provides the first detailed analysis of lepton flavor violation in an A4-symmetric supersymmetric model with predictions for experimental observables.

Findings

Branching ratios scale as u^2 generally, u^4 with cancellations.

Current bounds favor small u or tan(beta) for certain mass ranges.

Future experiments will significantly restrict the model's parameter space.

Abstract

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 A4 X Z3 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 approx 0.01 and small tan(beta) or m_{SUSY} and 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.