The status of the strong coupling from tau decays in 2016

Understand

While the idea of using the operator product expansion (OPE) to extract the strong coupling from hadronic $\tau$ decay data is not new, there is an ongoing controversy over how to include quark-hadron "duality violations" (i.e., resonance effects) which are not described by the OPE.

• One approach attempts to suppress duality violations enough that they might become negligible, but pays the price of an uncontrolled OPE truncation.
• We critically examine a recent analysis using this approach and show that it fails to properly account for non-perturbative effects, making the resulting determination of the strong coupling unreliable.
• In a different approach duality violations are taken into account with a model, avoiding the OPE truncation.