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 $\mathrm{SO}\left(10\right)\mathrm{}$ models and heterotic superstring models with $E_6$ 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 $Br\left(\overrightarrow{\tau }\mu \gamma \right)\sim {10}^{-9}$ and $Br\left(\overrightarrow{\tau }3\mu \right)\sim {10}^{-10}.$ In contrast, model II may show branching ratios $Br\left(\overrightarrow{\tau }e\gamma \right)\sim {10}^{-8}$ and $Br\left(\overrightarrow{\tau }3e\right)\lesssim {10}^{-9}$ over a sizable region of the parameter space, large enough to be tested by experiments in the near future.

• Received 25 February 2002

DOI:https://doi.org/10.1103/PhysRevD.66.034008