Ghost-gluon coupling, power corrections, and ^MS¯¯¯¯¯ from twisted-mass lattice QCD at Nf=2

Abstract

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 ^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 ^MS¯¯¯¯¯¯ is discussed.