Vector meson dominance in photon structure functions at small $x$ from holography

TL;DR

This paper uses holographic QCD to analyze photon structure functions at small x, demonstrating vector meson dominance and matching experimental data through Pomeron exchange models.

Contribution

It introduces a holographic approach to compute photon structure functions incorporating vector meson dominance and Pomeron exchange, aligning with experimental results.

Findings

Photon structure functions agree with experimental data

Vector meson dominance is realized in the holographic model

Calculations of longitudinal structure functions are consistent with observations

Abstract

We investigate the photon structure functions via the photon-photon and photon-vector meson scattering within the framework of holographic QCD, focusing on the small Bjorken $x$ region and assuming that the Pomeron exchange dominates. The quasi-real photon structure functions are formulated as the convolution of the known U(1) vector field wave function with the Brower-Polchinski-Strassler-Tan (BPST) Pomeron exchange kernel in the five-dimensional AdS space. Assuming the vector meson dominance, the photon structure functions can be calculated in a different way with the BPST kernel and vector meson gravitational form factor, which can be obtained in a bottom-up AdS/QCD model, for the Pomeron-vector meson coupling. It is shown that the obtained $F_2$ structure functions in the both ways agree with the experimental data, which implies the realization of the vector meson dominance within the present model setup. Calculations for the longitudinal structure function and the longitudinal-to-transverse ratio are also presented.