Decoupling of heavy sneutrinos in low-scale seesaw models

Abstract

There have been some recent claims in the literature about large right-handed sneutrinos contributions to lepton flavor violating observables like $\mu \to 3e$ or $\mu - e$ conversion in nuclei in supersymmetric low-scale seesaw models. These large contributions originate from $Z$-penguin diagrams which show a much weaker dependence on the heavy masses than the photonic contributions. We have traced this to an error in the evaluation of the corresponding loop amplitudes which has propagated in the literature. We explicitly show that after correcting this mistake the $Z$-penguins show the expected decoupling behavior. Moreover, the reported dominance of the $Z$-penguin over the photonic contributions disappears as well.