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Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory

M. Ramsey-Musolf·Mark B. Wise
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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 $π^0\to e^+ e^-$ 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.

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M. Ramsey-Musolf, Mark B. Wise. 2002-05-03. Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory. https://doi.org/10.1103/physrevlett.89.041601

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