Violations of Quark-Hadron Duality in Low-Energy Determinations of $α_s$

Using the spectral functions measured in $τ$ decays, we investigate the actual numerical impact of duality violations on the extraction of the strong coupling. These effects are tiny in the standard $α_s(m_τ^2)$ determinations from integrated distributions of the hadronic spectrum with pinched weights, or from the total $τ$ hadronic width. The pinched-weight factors suppress very efficiently the violations of duality, making their numerical effects negligible in comparison with the larger perturbative uncertainties. However, combined fits of $α_s$ and duality-violation parameters, performed with non-protected weights, are subject to large systematic errors associated with the assumed modelling of duality-violation effects. These uncertainties have not been taken into account in the published analyses, based on specific models of quark-hadron duality.

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