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→μγ )∼10^-9 and Br(τ→3μ)∼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.