Saturation in Deep Inelastic Scattering from AdS/CFT

TL;DR

This paper uses AdS/CFT to analyze deep inelastic scattering at small Bjorken x, demonstrating geometric scaling and unitarity restoration in the saturated regime, with predictions matching experimental data.

Contribution

It introduces a holographic approach to saturation in deep inelastic scattering, connecting AdS/CFT duality with QCD phenomenology and providing testable predictions.

Findings

Agreement with experimental F_2 data within 6% accuracy

Demonstration of geometric scaling in the saturated regime

Prediction of cross section dependence on (Q/Q_s)^2

Abstract

We analyze deep inelastic scattering at small Bjorken x, using the approximate conformal invariance of QCD at high energies. Hard pomeron exchanges are resummed eikonally, restoring unitarity at large values of the phase shift in the dual AdS geometry. At weak coupling this phase is imaginary, corresponding to a black disk in AdS. In this saturated regime, cross sections exhibit geometric scaling and have a simple universal form, which we test against available experimental data for the proton structure function F_2(x,Q^2). We predict, in particular, the dependence of the cross section on the scaling variable (Q/Q_s)^2 in the deeply saturated region, where Q_s is the usual saturation scale. We find agreement with current data on F_2 in the kinematical region 0.5 < Q^2 < 10 GeV^2, x < 10^-2, with an average 6% accuracy. We conclude by discussing the relation of our approach with the commonly used dipole formalism.