Jean Pierre Leroy

Is the QCD ghost dressing function finite at zero momentum

We show that a finite non-vanishing ghost dressing function at zero momentum satisfies the scaling properties of the ghost propagator Schwinger-Dyson equation. This kind of Schwinger-Dyson solutions may well agree with lattice data and provides an interesting alternative to the widely spread claim that the gluon dressing function behaves like the inverse squared ghost dressing function, a claim which is at odds with lattice data. We demonstrate that, if the ghost dressing function is less singular than any power of p, it must be finite non-vanishing at zero momentum: any logarithmic behaviour is for instance excluded. We add some remarks about coupled Schwinger-Dyson analyses.

Preliminary Calculation of αS from Green Functions with Dynamical Quarks

We present preliminary results on the computation of the QCD running coupling constant in the scheme and Landau gauge with two flavours of dynamical Wilson quarks. Gluon momenta range up to about 7 GeV (β = 5.6, 5.8 and 6.0) with a constant dynamical-quark mass. This range already allows to exhibit some evidence for a sizable 1/μ2 correction to the asymptotic behaviour, as in the quenched approximation, although a fit without power corrections is still possible with a reasonable χ2. Following the conclusions of our quenched study, we take into account 1/μ2 correction to the asymptotic behaviour. We find = 264(27) MeV × [a−1(5.6,0.1560)/2.19 GeV], which leads to αs(MZ) = 0.113(3)(4). The latter result has to be taken as a preliminary indication rather than a real prediction in view of the systematic errors still to be controlled. Still, being two sigmas below the experimental result makes it very encouraging.

Lattice calculation of 1/p2 corrections to αs and of Λ(QCD) in the MOM-tilde scheme

We report on very strong evidence of the occurrence of power terms in

Divergent IR gluon propagator from Ward-Slavnov-Taylor identities?

\as(p)

Lattice measurement of the couplings g-hat∞ and g D*Dπ

, the QCD running coupling constant in the

Lattice calculation of 1/p2corrections to αsand of Λ(QCD)in theMOM-tilde scheme

\widetilde{MOM}

Lattice measurement of the IsgurWise functions t 1 / 2 and t 3 / 2

scheme, by analyzing non-perturbative measurements from the lattice three-gluon vertex between 2.0 and 10.0 GeV at zero flavor. While putting forward the caveat that this definition of the coupling is a gauge dependent one, the general relevance of such an occurrence is discussed. We fit

Lattice measurement of the couplings g-hatinfty and g D*Dpi

\Lambda_{\bar{\rm MS}}^{(n_f=0)}= 237 \pm 3 ^{+ 0}_{-10}

Instantons and the condensate

MeV in perfect agreement with the result obtained by the ALPHA group with a totally different method. The power correction to

Lattice calculation of 1/p2 corrections to alphas and of Lambda(QCD) in the MOM-tilde scheme

\as(p)