Computation of the strong coupling in QCD with two dynamical flavours
Michele Della Morte, Roberto Frezzotti, Jochen Heitger, Juri Rolf, Rainer Sommer, Ulli Wolff
TL;DR
The paper tackles the non-perturbative determination of the QCD coupling's running with two dynamical flavours by employing a finite-volume Schrödinger functional framework and a step-scaling approach to connect hadronic and perturbative energies. It performs a controlled continuum extrapolation to extract the Lambda-parameter, yielding Λ_MSbar^(2) = 245(16)(16) MeV (for r0 = 0.5 fm) and relating this to a hadronic scale via L_max/r0, with data collected at lattice spacings between 0.07 and 0.1 fm. The work rigorously analyzes discretization effects, tuning precision, and the computational strategy (including sampling and topology considerations) to ensure robust non-perturbative results beyond the quenched approximation. Overall, it provides a foundational, non-perturbative bridge between hadronic observables and high-energy QCD for two dynamical flavours, setting the stage for more precise unquenched determinations.
Abstract
We present a non-perturbative computation of the running of the coupling alpha_s in QCD with two flavours of dynamical fermions in the Schroedinger functional scheme. We improve our previous results by a reliable continuum extrapolation. The Lambda-parameter characterizing the high-energy running is related to the value of the coupling at low energy in the continuum limit. An estimate of Lambda*r_0 is given using large-volume data with lattice spacings a from 0.07 fm to 0.1 fm. It translates into Lambda_{MSbar}^{(2)}=245(16)(16) MeV [assuming r_0=0.5 fm]. The last step still has to be improved to reduce the uncertainty.