Are the low-momentum gluon correlations semiclassically determined?

We argue that low-energy gluodynamics can be explained in terms of semi-classical Yang-Mills solutions by demonstrating that lattice gluon correlation functions fit to instanton liquid predictions for low energies and, after cooling, in the whole range.Comment: 4 pages, revtex

On the IR behaviour of the Landau-gauge ghost propagator

We examine analytically the ghost propagator Dyson-Schwinger Equation (DSE) in the deep IR regime and prove that a finite ghost dressing function at vanishing momentum is an alternative solution (solution II) to the usually assumed divergent one (solution I). We furthermore find that the Slavnov-Taylor identities discriminate between these two classes of solutions and strongly support the solution II. The latter turns out to be also preferred by lattice simulations within numerical uncertainties.Comment: 15 pages, Axodraw neede

Modified instanton profile effects from lattice Green functions

We trace here instantons through the analysis of pure Yang-Mills gluon Green functions in the Landau gauge for a window of IR momenta (0.4 GeV $< k < 0.9$ GeV). We present lattice results that can be fitted only after substituting the BPST profile in the Instanton liquid model (ILM) by one based on the Diakonov and Petrov variational methods. This also leads us to gain information on the parameters of ILM.Comment: 32 pagex, 6 figure

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.Comment: 8 pages, 2 figure

Non-Perturbative Approach to the Landau Gauge Gluodynamics

We discuss a non-perturbative lattice calculation of the ghost and gluon propagators in the pure Yang-Mills theory in Landau gauge. The ultraviolet behaviour is checked up to NNNLO yielding the value \Lambda^{n_f=0}_{\ms}=269(5)^{+12}_{-9}\text{MeV}, and we show that lattice Green functions satisfy the complete Schwinger-Dyson equation for the ghost propagator for all considered momenta. The study of the above propagators at small momenta showed that the infrared divergence of the ghost propagator is enhanced, whereas the gluon propagator seem to remain finite and non-zero. The result for the ghost propagator is consistent with the analysis of the Slavnov-Taylor identity, whereas, according to this analysis, the gluon propagator should diverge in the infrared, a result at odds with other approaches.Comment: To appear in the proceedings of the workshop "Hadron Structure and QCD: from LOW to HIGH energies" (St. Petersburg, Russia, 20-24 September 2005

A Ghost Story II: Ghosts, Gluons and the Gluon condensate beyond the IR of QCD

Beyond the deep IR, the analysis of ghost and gluon propagators still keeps very interesting non-perturbative information. The Taylor-scheme coupling can be computed and applied to obtain the $\Lambda_{\rm QCD}$ parameter from Landau gauge lattice simulations. Furthermore, a dimension-two gluon condensate, that can be understood in the instanton liquid model, plays an important role in the game.Comment: 12 pp., 3 fig

Quark pseudoscalar vertex and quark mass function with clover fermions : spontaneous symmetry breaking, OPE, symmetry restoration at small volume

We study the quark mass function on hypercubic lattices, in a large range of physical volumes and cutoffs. To avoid the very large Wilson term artefact, we exploit the relation between the quark mass function and the pseudoscalar vertex in the continuum. We extrapolate to the chiral limit. In function of the physical volume, we observe a striking discontinuity in the properties of chiral extrapolation around a physical volume L_c 6 (GeV}^{-1}=1.2 fm. It is present in the quark mass function, which collapses to zero, as well as in the pion mass and the quark condensate as directly calculated from the pseudoscalar correlator. It is strongly reminiscent of the phenomenon of chiral symmetry restoration observed by Neuberger and Narayanan at $N_C=\infty$ around the same physical length. In the case of spontaneous symmetry breaking, we confirm that the OPE of the quark mass function, involving the quark condensate, is not operative at the available momenta, even taking into account the unusually large high order corrections to the Wilson coefficient calculated by Chetyrkin and Maier ; the gap remains large, around a factor 2, even at the largest momenta available to us (p \simeg GeV)Comment: 31 pages, 8 figures Comments added, one figure suppressed, various typos correcte

Constraints on the IR behaviour of gluon and ghost propagator from Ward-Slavnov-Taylor identities

We consider the constraints of the Slavnov-Taylor identity of the IR behaviour of gluon and ghost propagators and their compatibility with solutions of the ghost Dyson-Schwinger equation and with the lattice picture.Comment: 5 pages, 2 figure