Probing lepton-number/flavour-violation in semileptonic τ decays into two mesons

The evaluation, systematic analysis and numerical study of the semileptonic τ -lepton decays with two mesons in the final state has been made in the frame of the standard model extended by right handed neutrinos. In the analysis, heavy-neutrino nondecoupling effects, finite quark masses, quark and meson mixings, finite widths of vector mesons, chiral symmetry breakings in vector-meson–pseudoscalar-meson vertices and effective Higgs-boson– pseudoscalar-meson couplings have been included. Numerical estimates reveal that the decays τ− → e−π−π+, τ− → e−K−K+ and τ− → e−K0K̄0 have branching ratios of the order of 10−6, close to present-day experimental sensitivities. PACS number(s): 13.35.Dx, 14.60.St, 12.39.Fe