The τ→ν<inf>τ</inf>ηπ process in and beyond QCD

We estimate various sources of the τ→ντηπ process by using QCD-duality sum rule information on the decay constants of standard and exotic mesons. We use the π→lνl decay in order to constrain the effects of new interactions. We conclude from our analysis that in al cases, the τ→ντηπ branching ration is small. We also point out that the present data on the τ→νπ process already provide an upper limit of 0.1% on the ηπ mode while the τ→ντKK̄ data imply an upper limit of 0.5% if the a0 (980)- meson is a four-quark state. © 1987.