Possible duality violations in τ decay and their impact on the determination of αs

We discuss the issue of duality violations in hadronic tau decay. After introducing a physically motivated ansatz for duality violations, we estimate their possible size by fitting this ansatz to the tau experimental data provided by the ALEPH Collaboration. Our conclusion is that these data do not exclude significant duality violations in tau decay. This may imply an additional systematic error in the value of αs(mτ), extracted from tau decay, as large as δαs(mτ)∼0.003-0.010. © 2009 The American Physical Society.