Semileptonic lepton-number- and/or lepton-flavor-violating tau decays in Majorana neutrino models

Motivated by the recent investigation of neutrinoless tau-lepton decays by the CLEO collaboration, we perform a systematic analysis of such decays in a possible new-physics scenario with heavy Dirac and/or Majorana neutrinos, including heavy-neutrino nondecoupling effects, finite quark masses, and quark as well as meson mixings. We find that the tau-lepton decays into an electron or muon and a pseudoscalar or vector meson can have branching ratios close to the experimental sensitivity. Numerical estimates show that the predominant decay modes of this kind are tau(-) --> e(-) phi, tau(-) --> e(-) rho(0),and tau(-) --> e(-) pi(0), with branching ratios of the order of 10(-6).