Effects of Renormalon and Resummation Schemes on Extractions of the Strong Coupling alpha_s(m_Z)

We examine effective field theory extractions of the strong coupling constant alpha_s(m_Z) from e^+e^− event shapes, with an emphasis on the role of non-perturbative renormalon cancellation schemes and perturbative scale variations in describing the physics of thrust, the canonical event shape variable. We calculate e^+e^− thrust to N^3LL resummed and three-loop fixed-order accuracy in matched Soft Collinear Effective Theory (SCET). We consider the effect of different schemes to cancel renormalon ambiguities between perturbative and the dominant nonperturbative effects on event shapes, and choices of perturbative profiles scales in the resummed perturbative predictions. We then perform a global fit of the resulting distributions to available data spanning center-of-mass energies between 35-207 GeV. Relevant subsets of our results are consistent with prior SCET extractions of alpha_s(m_Z) available in the literature. However, we also reach a number of additional conclusions. Critically, we observe that the combined effect of altering the renormalon cancellation scheme and/or profile parameters can lead to noticeably different extracted values of alpha_s and the dominant nonperturbative shift parameter Omega_1. This may have to be considered as an additional systematic theory uncertainty in these extractions, possibly reducing the current tension that exists between these extracts and the PDG world average. We suggest that fits performed over windows dominated by dijet (rather than tri- or multi-jet) events are typically of a higher quality than those that extend into the far-tails of distributions, providing a roadmap for further theoretical and experimental improvements.