The gradient flow coupling at high-energy and the scale of SU(3) Yang-Mills theory

Abstract

Using finite size scaling techniques and a renormalization scheme based on the Gradient Flow, we determine non-perturbatively the ${\hat{I}}^2$-function of the $SU(3)$ Yang-Mills theory for a range of renormalized couplings ${\bar{g}}^2\sim 1-12$. We perform a detailed study of the matching with the asymptotic NNLO perturbative behavior at high-energy, with our non-perturbative data showing a significant deviation from the perturbative prediction down to ${\bar{g}}^2\sim 1$. We conclude that schemes based on the Gradient Flow are not competitive to match with the asymptotic perturbative behavior, even when the NNLO expansion of the ${\hat{I}}^2$-function is known. On the other hand, we show that matching non-perturbatively the Gradient Flow to the Schrödinger Functional scheme allows us to make safe contact with perturbation theory with full control on truncation errors. This strategy allows us to obtain a precise determination of the $\hat{I}›$-parameter of the $SU(3)$ Yang-Mills theory in units of a reference hadronic scale ($\sqrt{8t_0}\hat{I}{›}_{\overline{\mathrm{MS}}}=0.6227(98)$), showing that a precision on the QCD coupling below 0.5\% per-cent can be achieved using these techniques.

LaTeX, 55 pages