Direct calculation of hadronic light-by-light scattering

TL;DR

This paper presents the first lattice QCD calculations of hadronic light-by-light scattering amplitudes, focusing on forward scattering, to improve theoretical predictions of the muon anomalous magnetic moment.

Contribution

It introduces a lattice QCD approach to compute hadronic light-by-light scattering amplitudes, including a strategy for evaluating their impact on muon g-2.

Findings

Initial results include the fully quark-connected contribution.

Forward scattering amplitudes can be related to experimental cross sections.

A new strategy for calculating the muon anomalous magnetic moment contribution.

Abstract

We report calculations of hadronic light-by-light scattering amplitudes via lattice QCD evaluation of Euclidean four-point functions of vector currents. These initial results include only the fully quark-connected contribution. Particular attention is given to the case of forward scattering, which can be related via dispersion relations to the $\gamma^* \gamma^* \to$ hadrons cross section, and thus allows lattice data to be compared with phenomenology. We also present a strategy for computing the hadronic light-by-light contribution to the muon anomalous magnetic moment.