Dispersion relation for hadronic light-by-light scattering: subleading contributions

Abstract

In this work, we present an evaluation of subleading effects in the hadronic light-by-light contribution to the anomalous magnetic moment of the muon. Using a recently derived optimized basis, we first study the matching of axial-vector contributions to short-distance constraints at the level of the scalar basis functions, finding that also the tails of the pseudoscalar poles and tensor mesons play a role. We then develop a matching strategy that allows for a combined evaluation of axial-vector and short-distance constraints, supplemented by an estimate of tensor-meson contributions based on simplified assumptions for their transition form factors. Uncertainties are primarily propagated from the axial-vector transition form factors and the variation of the matching scale, but we also consider estimates of the low-energy effect of hadronic states not explicitly included. In total, we obtain ${\left.{a}_{\mu}^{\textrm{HLbL}}\right|}_{\textrm{subleading}}$ = 33.2(7.2) × 10⁻¹¹, which in combination with previously evaluated contributions in the dispersive approach leads to ${\left.{a}_{\mu}^{\textrm{HLbL}}\right|}_{\textrm{total}}$ = 101.9(7.9) × 10⁻¹¹.