The case for duality violations in the analysis of hadronic τ decays

© 2016 World Scientific Publishing Company. In this review, we discuss why, in the determination of αs(mτ2) from hadronic τ decays, two important assumptions made in most of previous analyses, namely the neglect of higher-dimension condensates and of duality violations (DVs), have introduced uncontrolled systematic errors into this determination. Although the use of pinched weights is usually offered as a justification of these assumptions, we explain why it is not possible to simultaneously suppress these two contributions; particularly since the Operator Product Expansion (OPE) is expected to be an asymptotic, rather than a convergent expansion. There is not only experimental and theoretical evidence for DVs but they also affect the extraction of αs(mτ2).