Alain Le Yaouanc

Non-perturbative power corrections to ghost and gluon propagators

We study the dominant non-perturbative power corrections to the ghost and gluon propagators in Landau gauge pure Yang-Mills theory using OPE and lattice simulations. The leading order Wilson coefficients are proven to be the same for both propagators. The ratio of the ghost and gluon propagators is thus free from this dominant power correction. Indeed, a purely perturbative fit of this ratio gives smaller value ( 270MeV) of Λ than the one obtained from the propagators separately( 320MeV). This argues in favour of significant non-perturbative ~ 1/q2 power corrections in the ghost and gluon propagators. We check the self-consistency of the method.

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.

coupling (gB*Bπ,gD*Dπ); A quark model with Dirac equation

We discuss the strong coupling of heavy mesons to a pion g, in the heavy quark limit. This quantity is quite remarkable since its values as estimated by different methods (various quark models and the QCD sum rules), are surprisingly different. The present quark models are mostly based on free spinors and their predictions depend crucially on the choice of the light quark mass. We propose a quark model based on the Dirac equation in a central potential, which gives a more refined description of Dirac spinors. We show that within such a Dirac model, the value of g is stable and large: g = 0.6(1), where we assume no quark current renormalization ((g_A)q = 1). Such a large result is strongly constrained by requiring that the model parameters fit the spectrum; we show that this implies a large ``effective light mass. It is also supported phenomenologically by a similar situation with heavy baryons, as well as by experience with nucleon (if one invokes additivity). We also calculate the couplings to heavy meson excitations, and show that the Adler-Weisberger sum rule is well saturated by a few levels (in contrast to the case of small g). We discuss uncertainties of our approach, and rise several questions which remain to be answered. The main mystery is the large, unusual discrepancy with QCD sum rules for g, whereas a good agreement is found for orbital excitations.

Possible explanation of the discrepancy of the light-cone QCD sum rule calculation of g(D*Dpi) coupling with experiment

The introduction of an explicit negative radial excitation contribution in the hadronic side of the light cone QCD sum rule (LCSR) of Belyaev, Braun, Khodjamirian and Ruckl, can explain the large experimental value of g(D*Dpi), recently measured by CLEO. At the same time, it considerably improves the stability of the sum rule when varying the Borel parameter.The introduction of an explicit negative radial excitation contribution in the hadronic side of the light cone QCD sum rule (LCSR) of Belyaev, Braun, Khodjamirian and Ruckl, can explain the large experimental value of g(D*Dpi), recently measured by CLEO. At the same time, it considerably improves the stability of the sum rule when varying the Borel parameter.

q\(\bar q\)g Hybrid mesons in ψ → γ+hadrons

AbstractWe study the hadronic decay of qn

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

bar q

The controversy about "1/m_Q duality violation" ; a quark model point of view

ng hybrid mesons. To that aim we establish the connection between the diatomic-molecule like wave functions and the standard qn