* Astronomy

Title: Enhancing l_i \to 3 l_j with the Z^0-penguin
Authors: M. Hirsch, F. Staub, A. Vicente

Lepton flavour violation (LFV) has been observed in neutrino oscillations. For charged lepton FV decays only upper limits are known, but sizable branching ratios are expected in many neutrino mass models. High scale models, such as the classical supersymmetric seesaw, usually predict that decays l_i \to 3 l_j are roughly a factor \alpha smaller than the corresponding decays l_i \to l_j \gamma. Here we demonstrate that the Z^0-penguin diagram can give an enhancement for decays l_i \to 3 l_j in many extensions of the MSSM. We first discuss why the Z^0-penguin is not dominant in the MSSM with seesaw and show that much larger contributions from the Z^0-penguin are expected in general. We then demonstrate the effect numerically in two example models, namely, the supersymmetric inverse seesaw and R-parity violating supersymmetry.

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