On Lepton Flavor Violation in Tau Decays

We study lepton flavor violation (LFV) in tau decays induced by heavy Majorana neutrinos within two models: (I) the Standard Model with additional right–handed heavy Majorana neutrinos, i.e., a typical seesaw–type model; (II) the Standard Model with left–handed and right–handed neutral singlets, which are inspired by certain scenarios of SO(10) models and heterotic superstring models with E6 symmetry. We calculate various LFV branching ratios and a T–odd asymmetry. The seesaw Model I predicts very small branching ratios for LFV processes in most of the parameter space, although in a very restricted parameter region it can reach maximal branching ratios Br(τ → �γ )∼10 −9 and Br(τ → 3� )∼10 −10 . In contrast, Model II may show branching ratios Br(τ → eγ)∼10 −8 and Br(τ → 3e) < ∼ 10 −9 , over a sizable region of the parameter space, large enough to be tested by experiments in the near future.