Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment reexamined

We discuss the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment a_^lbl, paying particular attention to the consistent matching between the short- and the long-distance behavior of the light-by-light scattering amplitude. We argue that short-distance QCD imposes strong constraints on this amplitude overlooked in previous analyses. We find that accounting for these constraints leads to approximately 50% increase in the central value of a_^lbl, compared to commonly accepted estimates (see, e. g. , M. Davier, S. Eidelman, A. Hocker, and Z. Zhang, Eur. Phys. J. C 31, 503 (2003). ). The hadronic light-by-light scattering contribution becomes a_^lbl=136 (25) 10^-11, thereby shifting the standard model prediction closer to the experimental value.