Non-minimal coupling contribution to DIS at low $x$ in Holographic QCD

TL;DR

This paper introduces a non-minimal coupling in holographic QCD models that improves the fit to low-x deep inelastic scattering data, aligning with effective field theory expectations and revealing insights into the QCD Pomeron and glueball spectrum.

Contribution

It proposes and tests a new non-minimal coupling between the vector gauge field and the graviton Regge trajectory in holographic QCD, enhancing data agreement.

Findings

Excellent fit to DIS data with chi squared of 1.1

Coupling scale around 6 GeV matches EFT predictions

Corrections linked to glueball mass gap

Abstract

We consider the effect of including a non-minimal coupling between a $U(1)$ vector gauge field and the graviton Regge trajectory in holographic QCD models. This coupling describes the QCD interaction between the quark bilinear electromagnetic current and the Pomeron. We test this new coupling against DIS data at low Bjorken $x$ and obtain an excellent fit with a chi squared of 1.1 over a very large kinematical range in the photon virtuality $Q^2<400 \ {\rm GeV}^2$ and for $x<10^{-2}$. The scale of the new dimension full coupling, which arises from integrating higher spin fields, is of order $6\ {\rm GeV}$. This value matches precisely the expectations from effective field theory, which indicate that such corrections are controlled by the mass gap between the spin two and spin four glueballs that are described holographically by the graviton and spin four field in the graviton Regge trajectory, respectively