Ghost-gluon coupling, power corrections and Ams from lattice QCD with a dynamical charm

We present results concerning the nonperturbative evaluation of the ghost-gluon running QCD coupling constant from Nf=2 twisted-mass lattice calculations. A novel method for calibrating the lattice spacing, independent of the string tension and hadron spectrum, is presented with results in agreement with previous estimates. The value of Λ¯¯¯¯¯¯MS is computed from the running of the QCD coupling only after extrapolating to zero dynamical quark mass and after removing a nonperturbative operator-product expansion contribution that is assumed to be dominated by the dimension-two ⟨A2⟩ gluon condensate. The effect due to the dynamical quark mass in the determination of Λ¯¯¯¯¯¯MS is discussed.
We are particularly indebted to A. Le Yaouanc, J. P. Leroy, and J. Micheli for participating in many fruitful discussions at the preliminary stages of this work and to S. F. Reker and G. C. Rossi for their very attentive reading of the manuscript and valuable comments. We also thank the IN2P3 Computing Center (CNRS-Lyon), the apeNEXT computing laboratory (Rome), and the computing center at IDRIS (CNRS-Orsay) for provinding numerical resources. J. R.-Q. is indebted to the Spanish MICINN for the support from research Project No. FPA2009-10773 and to "Junta de Andalucia'' from Project No. P07FQM02962.