No abstract

Relating the forward light-by-light scattering to energy weighted integrals of the γ * γ fusion cross sections, with one real photon (γ) and one virtual photon (γ * ), we find two new exact superconvergence relations. They complement the known super-convergence relation based on the extension of the GDH sum rule to the light-light system. We also find a set of sum rules for the low-energy photon-photon interaction. All of the new relations are verified here exactly at leading order in scalar and spinor QED. The super-convergence relations, applied to the γ * γ production of mesons, lead to intricate relations between the γγ decay widths or the γ * γ transition form factors for (pseudo-) scalar, axial-vector and tensor mesons. We discuss the phenomenological implications of these results for mesons in both the light-quark sector and the charm-quark sector.arXiv:1204.0740v2 [hep-ph]

We develop the formalism to provide an improved estimate for the hadronic light-by-light correction to the muon's anomalous magnetic moment a µ , by considering single meson contributions beyond the leading pseudo-scalar mesons. We incorporate available experimental input as well as constraints from light-by-light scattering sum rules to estimate the effects of axial-vector, scalar, and tensor mesons. We give numerical evaluations for the hadronic light-by-light contribution of these states to a µ . The presented formalism allows to further improve on these estimates, once new data for such meson states will become available.