Vladyslav Pauk

Single meson contributions to the muon’s anomalous magnetic moment

We develop the formalism to provide an improved estimate for the hadronic light-by-light correction to the muon’s anomalous magnetic moment

Lepton universality test in the photoproduction of

a_\mu

versus

aμ, by considering single meson contributions beyond the leading pseudoscalar 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

pairs on a proton target

a_\mu

Beam normal spin asymmetry for the ep âe Î (1232) process

aμ. The presented formalism allows one to further improve on these estimates, once new data for such meson states will become available.

Beam normal spin asymmetry for the

Relating the forward light-by-light scattering to energy weighted integrals of the \gamma* \gamma -fusion cross sections, with one real photon (\gamma) and one virtual photon (\gamma*), we find two new exact super-convergence 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 \gamma* \gamma -production of mesons, lead to intricate relations between the \gamma \gamma -decay widths or the \gamma* \gamma -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.