Axial vector transition form factors in holographic QCD and their contribution to the anomalous magnetic moment of the muon
Abstract
We evaluate axial vector transition form factors in holographic QCD models that have been shown to reproduce well recent experimental and theoretical results for the pion transition form factor. Comparing with L3 data on f_{1}→γ γ^{*} we find remarkable agreement regarding the shape of singlevirtual form factors. In the doublevirtual case, the holographic results differ strongly from a simple dipole form, and this has an important impact on the corresponding estimate of the axial vector contribution to the anomalous magnetic moment of the muon a_{μ} through hadronic lightbylight scattering. We demonstrate that hardwall models satisfy the MelnikovVainshtein shortdistance constraint for the latter, if and only if the infinite tower of axial vector states is included. The results for a_{μ}, however, are strongly dominated by the first few resonances. Numerically, these results turn out to be surprisingly large: (2.9  4.1 )×10^{10} in the hardwall models, 57%58% of which are due to the longitudinal contribution, which is the one responsible for the MelnikovVainshtein shortdistance constraint. Rescaling the holographic result to obtain an optimal fit of L3 data, but then matching only 52% of the asymptotic constraint, the result is reduced to 2.2 (5 )×10^{10}, which is still significantly larger than most previous phenomenological estimates of the axial vector exchange contribution.
 Publication:

Physical Review D
 Pub Date:
 June 2020
 DOI:
 10.1103/PhysRevD.101.114015
 arXiv:
 arXiv:1912.01596
 Bibcode:
 2020PhRvD.101k4015L
 Keywords:

 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 23 pages, 5 figures, 4 tables