Longitudinal short-distance constraints on hadronic light-by-light scattering and tensor meson contributions to the muon $g-2$

TL;DR

This paper investigates how tensor mesons in holographic QCD can improve the matching of short-distance constraints on hadronic light-by-light scattering, refining the muon g-2 theoretical estimates.

Contribution

It demonstrates that tensor mesons can fill the gap in short-distance constraints, enhancing the accuracy of hadronic light-by-light scattering calculations in holographic QCD.

Findings

Tensor mesons contribute significantly below 1.5 GeV.

They improve the matching of short-distance constraints to 100%.

The results align well with dispersive and lattice calculations.

Abstract

Short-distance constraints from the operator product expansion in QCD play an important role in the evaluation of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. While conventional hadronic models involving a finite number of resonances fail to reproduce the correct power laws implied by them, holographic QCD has been shown to naturally incorporate the Melnikov-Vainshtein constraint on the longitudinal amplitude following from the triangle anomaly in the asymmetric limit, where one photon virtuality remains small compared to the others. This is saturated by an infinite tower of axial vector mesons, and their numerical contribution to the muon $g-2$ in AdS/QCD models agrees rather well with a recent dispersive analysis and alternative approaches. However, the longitudinal short-distance constraint where all virtualities are large turns out to be matched only at the level of 81\%. In this Letter we show that tensor mesons, whose contribution to the muon $g-2$ has recently been found to be underestimated, can fill this gap, because in holographic QCD their infinite tower of excited mesons only contributes to the symmetric longitudinal short-distance constraint. Numerically, they give rise to a sizeable positive contribution from the low-energy region below 1.5 GeV, a small one from the mixed region, and a negligible one from the high-energy region, which could explain the remaining gap between the most recent dispersive and lattice results for the complete hadronic light-by-light contribution.