Hadronic light-by-light scattering contribution to g_{mu}-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 transition form factor based on large-N_C and short-distance properties of QCD. We derive a two-dimensional integral representation which allows to separate the generic features from the model dependence, in order to better control the latter. Finally, we sketch an effective field theory approach to hadronic light-by-light scattering which yields the leading logarithmic terms that are enhanced by a factor N_C. It also shows that the modeling of hadronic light-by-light scattering by a constituent quark loop is not consistent with QCD. 
Andreas Nyffeler (CPT Marseille)