Hadronic light-by-light scattering contribution to the muon g-2

We briefly review the current status of the hadronic light-by-light scattering correction to the muon g-2. Then we present our semi-analytical evaluation of the pion-pole contribution, using a description of the pion-photon-photon form factor based on large-N_C and short-distance properties of QCD. We also sketch an effective field theory approach to hadronic light-by-light scattering. In view of several still unsolved problems, our conservative estimate for the full hadronic light-by-light scattering contribution is a_{mu}(LbyL;had) = + 8 (4) x 10^{-10}.Comment: 4 pages including 2 figures, Latex, uses espcrc2.sty; Talk presented at the 9th International High-Energy Physics Conference in Quantum Chromodynamics (QCD 2002), Montpellier, France, 2-9 July 200

On some properties of the fourth-rank hadronic vacuum polarization tensor and the anomalous magnetic moment of the muon

Some short-distance properties of the fourth-rank hadronic vacuum polarization tensor are re-examined.Their consequences are critically discussed in the context of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon.Comment: Latex2e, 19 page

Chiral perturbation theory confronted with experiment

The general framework and the present status of the low energy theory of the standard model are briefly reviewed. Recent applications to a few topic of interest for the determinations of Vud and of Vus are discussedComment: Talk given at the DAPHNE 2004 Workshop, Frascati, June 7 - 11, 2004; 9 pages, uses frascatiphys.st

Minimal Hadronic Ansatz to Large-Nc QCD and Hadronic tau Decay

I report on some recent work done in collaboration with Santi Peris and Boris Phily (hep-ph/0007338) where, using the Aleph data on vector and axial-vector spectral functions, we test simple duality properties of QCD in the large-Nc limit which emerge in the approximation of a {\it minimal hadronic ansatz} of a spectrum of narrow states. These duality properties relate the short- and long-distance behaviours of specific correlation functions, which are order parameters of spontaneous chiral symmetry breaking, in a way that we find well supported by the data.Comment: 7 pages with 3 figures. Latex file. Contribution to the Euroconference QCD00, Montpellier, Franc

Unfactorizing Polychromatic Penguins

Firstly, I report on a recent work --carried out with T. Hambye and E. de Rafael-- on how to use the large-Nc expansion to calculate unfactorized contributions from the strong penguin operators, and their impact on observables such as epsilon'/epsilon and the Delta I = 1/2 rule. Secondly, based on work done with M. Golterman, I explain how this calculation allows one to predict some rather dramatic consequences for quenched QCD. This may help explain the present discrepancy between lattice and experimental results for epsilon'/epsilon. The emphasis of this article is put on the explanation of the method of calculation used, which is fully analytic. This allows one to build some intuition and understand the role played by the different hadronic scales in determining the size of the different contributions.Comment: 6 pages, 1 figure. Invited talk delivered at the "X Int. Conference on Quantum Chromodynamics", Montpellier, France, July 200

A new start for local composite operators

We present a formalism for local composite operators. The corresponding effective potential is unique, multiplicatively renormalizable, it is the sum of 1PI diagrams and can be interpreted as an energy-density. First we apply this method to $\lambda \Phi^4$ theory where we check renormalizability up to three loops and secondly to the Coleman-Weinberg model where the gauge independence of the effective potential for the local composite operator $\phi\phi^*$ is explicitely checked up to two loops.Comment: 20 page