The ντ-mass and the τ-decay modes

The behaviour of the different decay modes of the charged heavy lepton τ versus the neutrino ν_τ-mass is analyzed in detail. The τ→ν_τ A ₁ and τ→ν_τ K ^* decay rates have been evaluated using finite energy sum rules. The τ→ν_τ+ “Hadron Continuum” decay rate has been estimated within the framework of Quantum Chromodynamics (QCD). We find that the branching ratios of the semi-leptonic processes: τ→ν_τρ, τ→ν_τπ and τ→ν_τ+ “Hadron Continuum” are very sensitive to the value of the ν_τ-mass. Thus a more precise measurement of these branching ratios could provide an improved upper bound for the neutrino ν_τ-mass.