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

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

Hadronic Light-by-Light Contribution to Muon g-2: Status and Prospects

I review the recent calculations and present status of the hadronic light-by-light contribution to the muon g-2.Comment: 8 pages, 1 figure. Invited talk at PHIPSI08, International Conference on e+e- collisions from Phi to Psi, April 7-10 2008, Frascati, Italy. v2: Wrong year in one referenc

Syntactic structure and artificial grammar learning : The learnability of embedded hierarchical structures

Embedded hierarchical structures, such as ‘‘the rat the cat ate was brown’’, constitute a core generative property of a natural language theory. Several recent studies have reported learning of hierarchical embeddings in artificial grammar learning (AGL) tasks, and described the functional specificity of Broca’s area for processing such structures. In two experiments, we investigated whether alternative strategies can explain the learning success in these studies. We trained participants on hierarchical sequences, and found no evidence for the learning of hierarchical embeddings in test situations identical to those from other studies in the literature. Instead, participants appeared to solve the task by exploiting surface distinctions between legal and illegal sequences, and applying strategies such as counting or repetition detection. We suggest alternative interpretations for the observed activation of Broca’s area, in terms of the application of calculation rules or of a differential role of working memory. We claim that the learnability of hierarchical embeddings in AGL tasks remains to be demonstrated

Electroweak Physics

The status of precision electroweak measurements as of summer 2002 is reviewed. The recent results on the anomalous magnetic moment of the muon and on neutrino-nucleon scattering are discussed. Precision results on the electroweak interaction obtained by the experiments at the SLC, LEP and TEVATRON colliders are presented. The experimental results are compared with the predictions of the minimal Standard Model and are used to constrain its parameters, including the mass of the Higgs boson. The final LEP results on the direct search for the Higgs boson of the Standard Model are presented.Comment: Plenary talk presented at the 31st ICHEP, Amsterdam, The Netherlands, July 24-31, 200

A Critical Reassessment of Q7 and Q8 Matrix Elements

We compare recent theoretical determinations of weak matrix elements of the electroweak penguin operators Q7 and Q8. We pay special attention to the renormalization scheme dependence of these determinations as well as to the influence of higher dimension operators in the different approaches.Comment: 11 pages, latex; minor change

Matrix Elements of Electroweak Penguin Operators in the 1/Nc Expansion

It is shown that the K -> pi pi matrix elements of the four-quark operator Q_7, generated by the electroweak penguin-like diagrams of the Standard Model, can be calculated to first non-trivial order in the chiral expansion and in the 1/Nc expansion. Although the resulting B factors B_7^(1/2) and B_7^(3/2) are found to depend only logarithmically on the matching scale, mu, their actual numerical values turn out to be rather sensitive to the precise choice of mu in the GeV region. We compare our results to recent numerical evaluations from lattice-QCD and to other model estimates.Comment: 10 pages, LateX, two figures (inserted). Improved comparison with the lattice results. Results unchange

Supersymmetric two-loop contributions to the anomalous magnetic moment of the muon

Recent results of two interesting classes of supersymmetric two-loop contributions to (g-2)_mu are presented. Two-loop diagrams involving a closed sfermion loop can amount to 5*10^{-10} or almost one standard deviation of the current experimental uncertainty, and two-loop diagrams with a closed chargino/neutralino loop can be similarly large. The dependence of these two classes on the unknown supersymmetric parameters and the sensitivity on existing experimental constraints on the parameter space are quite different. We also comment on the calculational techniques, in particular the large mass expansion and the treatment of gamma_5 and the epsilon-tensor.Comment: 5 pages, Talk at Loops & Legs 2004, DESY Workshop on Elementary Particle Theory in Zinnowitz/Usedo