Anomalous magnetic moment of the muon: towards a reconciliation between experiment and standard model

by Andreas NYFFELER (Centre de Physique Théorique, Marseille)

Friday 25 Jan 2002, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

I briefly review the various contributions to g-2 of the muon in the standard model, in particular the hadronic corrections which dominate the theoretical uncertainties. I then present our recent semi-analytical evaluation of the dominant contribution in hadronic light-by-light scattering, due to the exchange of a neutral pion. We have derived a two-dimensional integral representation for the corresponding two-loop diagrams which is valid for a rather general class of pion-photon-photon transition form factors. Using a form factor based on large-N_C and short-distance properties of QCD, we obtain a _m = (+8.3 ± 1.2) x 10^-10 from all light pseudoscalar states. Our calculation has thereby revealed a sign error in recent evaluations of this contribution and our result reduces substantially the discrepancy between the experimental value announced by the Muon g-2 Collaboration at Brookhaven Laboratory and the prediction in the standard model. Finally, I also discuss an effective field theory approach which offers the possibility of a systematic treatment of all the contributions to hadronic light-by-light scattering.