Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory
Abstract
We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, \amulbl, in chiral perturbation theory that are enhanced by large logarithms and a factor of N_C. They depend on a low-energy constant entering pseudoscalar meson decay into a charged lepton pair. The uncertainty introduced by this constant is \pm 60\times 10^{-11}, which is comparable in magnitude to the present uncertainty entering the leading-order vacuum polarization contributions to the anomalous moment. It may be reduced to some extent through an improved measurement of the \pi^0\to e^+ e^- branching ratio. However, the dependence of \amulbl on non-logarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself. The extraction of information on new physics would require a future experimental value for the anomalous moment differing significantly from the 2001 result reported by the E821 collaboration.