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

Abstract

Motivated by the recent investigation of neutrinoless \ensuremath{\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 \ensuremath{\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 ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\varphi}, ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{e}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\rho}}}^{0}$, and ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{e}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$, with branching ratios of the order of ${10}^{\mathrm{\ensuremath{-}}6}$.