Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment revisited

TL;DR

This paper reassesses the hadronic light-by-light contribution to the muon g-2 by enforcing consistency between short-distance QCD constraints and the low-energy hadronic model. Using a minimal large-Nc framework that includes pseudoscalar and pseudovector exchanges and enforces correct asymptotics via the OPE, the authors obtain a central value of $a_\mu^{lbl}=136(25)\times 10^{-11}$, about 50% higher than prior estimates, which shifts the Standard Model prediction closer to the experimental result. The work highlights that previous analyses likely underestimated HLbL due to excessive damping of high-momentum contributions and emphasizes the importance of matching both regimes. While the pseudoscalar and pseudovector pieces are constrained and increase the central value, the pion box Nc^0 component remains challenging to pin down, motivating cautious uncertainty assessments for the full HLbL contribution.

Abstract

We discuss hadronic light-by-light scattering contribution to the muon anomalous magnetic moment a_μ^{\rm lbl}, paying particular attention to the consistent matching between the short- and the long-distance behavior of the light-by-light scattering amplitude. We argue that the short-distance QCD imposes strong constraints on this amplitude overlooked in previous analyses. We find that accounting for these constraints leads to approximately 50 per cent increase in the central value of a_μ^{\rm lbl}, compared to existing estimates. The hadronic light-by-light scattering contribution becomes a_μ^{\rm lbl}=136(25) \times 10^{-11}, thereby shifting the Standard Model prediction closer to the experimental value.

Figures (2)

• Figure 1: Hadronic contributions represented by quark loops: ($a$) vacuum polarization, ($b$) light-by-light scattering.
• Figure 2: Hadronic contributions to the light-by-light scattering: ($a$) charged pion loop, ($b$) exchange of neutral pion and other resonances.