Novel QCD Phenomena

TL;DR

This paper explores novel aspects of QCD using AdS/CFT correspondence to derive hadron wavefunctions and discusses new phenomenological effects such as single-spin asymmetries, diffraction phenomena, and heavy quark effects, revealing complex QCD dynamics.

Contribution

It introduces an analytic approach to QCD via AdS/CFT, linking fifth-dimension coordinates to impact variables, and explores new phenomenological features including initial/final-state interactions and hidden color effects.

Findings

Analytic light-front wavefunctions for mesons and baryons derived from AdS/CFT.

Identification of initial/final-state interactions causing single-spin asymmetries.

Evidence for hidden color and diffraction phenomena in nuclear wavefunctions.

Abstract

I discuss a number of novel topics in QCD, including the use of the AdS/CFT correspondence between Anti-de Sitter space and conformal gauge theories to obtain an analytically tractable approximation to QCD in the regime where the QCD coupling is large and constant. In particular, there is an exact correspondence between the fifth-dimension coordinate z of AdS space and a specific impact variable zeta which measures the separation of the quark constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions of mesons and baryons, the fundamental entities which encode hadron properties and allow the computation of exclusive scattering amplitudes. I also discuss a number of novel phenomenological features of QCD. Initial- and final-state interactions from gluon-exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam Tung relation in Drell-Yan reactions, and nuclear shadowing and non-universal antishadowing--leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. I also discuss tests of hidden color in nuclear wavefunctions, the use of diffraction to materialize the Fock states of a hadronic projectile and test QCD color transparency, and anomalous heavy quark effects. The presence of direct higher-twist processes where a proton is produced in the hard subprocess can explain the large proton-to-pion ratio seen in high-centrality heavy-ion collisions.