Search

This paper reports on a new procedure for the lattice spacing setting that takes advantage of the very precise determination of the strong coupling in the Taylor scheme. Although it can be applied for the physical scale setting with the experimental value of ¿MS¯¯¯¯¯¯ as an input, the procedure is particularly appropriate for relative ¿calibrations.¿ The method is here applied for simulations with four degenerate light quarks in the sea and leads to prove that their physical scale is compatible with the same one for simulations with two light and two heavy flavors., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Versión del editor

This paper is a first report on the determination of ^MS¯¯¯¯¯¯ from lattice simulations with 2+1+1 twisted-mass dynamical flavors via the computation of the ghost-gluon coupling renormalized in the MOM Taylor scheme. We show this approach allows a very good control of the lattice artefacts and confirm the picture from previous works with quenched and Nf=2 twisted-mass field configurations, which prove the necessity to include nonperturbative power corrections in the description of the running. We provide an estimate of ¿MS¯¯¯¯¯¯ in very good agreement with experimental results. To our knowledge, it is the first calculation with a dynamical charm quark which makes the running up to ¿s(MZ) much safer., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Versión del editor

This Letter reports on the first computation, from data obtained in lattice QCD with u, d, s, and c quarks in the sea, of the running strong coupling via the ghost-gluon coupling renormalized in the momentum-subtraction Taylor scheme. We provide readers with estimates of ¿MS¯¯¯¯¯¯(m2¿) and ¿MS¯¯¯¯¯¯(m2Z) in very good agreement with experimental results. Including a dynamical c quark makes the needed running of ¿MS¯¯¯¯¯¯ safer., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Postprint

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.

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., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Versión del editor

We give a more transparent understanding of the vacuum expectation value of the renormalized local operator A2 by relating it to the gluon propagator integrated over the momentum. The quadratically divergent perturbative contribution is subtracted and the remainder, dominantly due to the O(1/p2) correction to the perturbative propagator at large p2 is logarithmically divergent. This provides a transparent derivation of the fact that this O(1/p2) term is related to the vacuum expectation value of the local A2 operator and confirms a previous claim based on the operator product expansion (OPE) of the gluon propagator. At leading logarithms the agreement is quantitative, with a standard running factor, between the local A2 condensate renormalized as described above and the one renormalized in the OPE context. This result supports the claim that the BRST invariant Landau-gauge A2 condensate might play an important role in describing the QCD vacuum., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Postprint

We give a more transparent understanding of the vacuum expectation value of the renormalized local operator A2 by relating it to the gluon propagator integrated over the momentum. The quadratically divergent perturbative contribution is subtracted and the remainder, dominantly due to the O(1/p2) correction to the perturbative propagator at large p2 is logarithmically divergent. This provides a transparent derivation of the fact that this O(1/p2) term is related to the vacuum expectation value of the local A2 operator and confirms a previous claim based on the operator product expansion (OPE) of the gluon propagator. At leading logarithms the agreement is quantitative, with a standard running factor, between the local A2 condensate renormalized as described above and the one renormalized in the OPE context. This result supports the claim that the BRST invariant Landau-gauge A2 condensate might play an important role in describing the QCD vacuum. European Union Human Potential Program HPRN-CT- 2000-00145

We argue that the A2OPE condensate found in the Landau gauge on lattices, when an operator product expansion of Green's functions is performed, might be explained by instantons. We use cooling to estimate the instanton contribution and extrapolate back the result to the thermalized configuration. The resulting A2inst is similar to A2OPE., Universidad Pablo de Olavide. Departamento de Sistemas Físicos, Químicos y Naturales, Postprint