Neutral Meson Decays into Two Photons from Lattice QCD

TL;DR

This paper uses lattice QCD to study neutral meson decays into two photons, challenging the vector-meson dominance model and aiming to improve understanding of hadronic contributions relevant for precision tests of the Standard Model.

Contribution

It introduces a novel lattice QCD approach to compute neutral meson decay amplitudes into two photons, providing insights beyond traditional models like vector-meson dominance.

Findings

Vector-meson dominance poorly describes off-shell two-photon decays.

Lattice QCD can access two-photon decay amplitudes directly.

Results suggest the need for refined models in hadronic light-by-light calculations.

Abstract

A precision determination of the neutral-pion width would improve determinations of the splitting between the up- and down-quark masses, and matrix elements for the decay of neutral mesons into two photons could play a role in the attempt to probe beyond-the-Standard Model physics in muon $g-2$ experiments. The theoretical error is dominated by hadronic light-by-light diagrams, and since direct measurements are extremely difficult, model calculations factorize it into two-photon diagrams connected by the lightest hadrons. We employ perturbative techniques to express the photon as a superposition of QCD eigenstates accessible in lattice-QCD calculations and found that vector-meson dominance is a poor description of the two-photon decay process when both photons are off shell.