1202.1825 (M. Hirsch et al.)

Enhancing $l_i \to 3 l_j$ with the $Z^0$-penguin    [PDF]

M. Hirsch, F. Staub, A. Vicente

Lepton flavor 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 $\alpha$ maller 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.

View original: http://arxiv.org/abs/1202.1825