From gauge-string duality to strong interactions: a Pedestrian's Guide

TL;DR

The paper surveys how gauge-string duality, exemplified by the $N=4$ SYM / $AdS_5×S^5$ correspondence, illuminates strong-coupling aspects of QCD-like physics, including confinement mechanisms, finite-temperature transport, and real-time dynamics. It reviews holographic constructions that mimic confinement (hard wall, KS, Sakai-Sugimoto) and analyzes transport coefficients such as $\eta/s = 1/4\pi$ and the behavior of bulk viscosity in nonconformal settings, as well as expanding plasmas and hard probes (trailing strings, jet quenching) in holographic plasmas. The work highlights both the successes and limitations of holographic methods for QCD-like physics, emphasizing qualitative insights, universal results, and the need for incorporating finite-$N$ and finite-coupling effects. Overall, holography offers a powerful, complementary framework for understanding nonperturbative, real-time phenomena in strongly coupled gauge theories and the quark-gluon plasma, while stopping short of a complete, first-principles description of QCD.

Abstract

We survey recent progress in understanding the relation of string theory to quantum chromodynamics, focusing on holographic models of gauge theories similar to QCD and applications to heavy-ion collisions.