Deep inelastic scattering at strong coupling from gauge/string duality : the saturation line

TL;DR

This paper explores deep inelastic scattering at strong coupling using gauge/string duality, identifying the saturation line and mechanisms leading to unitarity at high energy, with implications for the dominance of diffractive processes.

Contribution

It determines the saturation line in gauge theories with string duals and reveals two distinct unitarity correction mechanisms depending on photon virtuality Q^2.

Findings

Unitarity corrections occur via single Pomeron exchange at low Q^2.

Multiple graviton exchanges dominate at high Q^2.

High-energy, large Q^2 cross-section is mainly diffractive.

Abstract

For gauge theories which admit a dual string description, we analyze deep inelastic scattering at strong 't Hooft coupling and high energy, in the vicinity of the unitarity limit. We discuss the onset of unitarity corrections and determine the saturation line which separates weak scattering from strong scattering in the parameter space of rapidity and photon virtuality. We discover that the approach towards unitarity proceeds through two different mechanisms, depending upon the photon virtuality Q^2 : single Pomeron exchange at relatively low Q^2 and, respectively, multiple graviton exchanges at higher Q^2. This implies that the total cross-section at high energy and large Q^2 is dominated by diffractive processes. This is furthermore suggestive of a partonic description where all the partons have transverse momenta below the saturation momentum and occupation numbers of order one.