String Theory and Quantum Chromodynamics

TL;DR

This paper surveys how gauge/gravity duality, particularly the AdS/CFT correspondence, connects string theory to QCD-like physics. It outlines the large-$N_c$ expansion and its correspondence to string genus, then details the AdS$_5\times S^5$/\={N}=4 SYM duality, including parameter mappings, symmetry matching, and the field/operator dictionary. Finite-temperature extensions reveal thermodynamic and hydrodynamic properties of strongly coupled plasmas, notably the universal viscosity-to-entropy ratio $\eta/s = 1/(4\pi)$ and its implications for the quark-gluon plasma, while a confining model via D4-branes demonstrates a Hawking-Page-type confinement/deconfinement transition with distinct spectra and quark potentials. The work discusses how these results relate to QCD phenomenology and RHIC data, the limitations of supergravity, and the broader challenge of deriving a full string dual for QCD at large $N_c$.

Abstract

I review recent progress on the connection between string theory and quantum chromodynamics in the context of the gauge/gravity duality. Emphasis is placed on conciseness and conceptual aspects rather than on technical details. Topics covered include the large-Nc limit of gauge theories, the gravitational description of gauge theory thermodynamics and hydrodynamics, and confinement/deconfinement thermal phase transitions.

Figures (23)

• Figure 1: One-loop gluon self-energy Feynman diagram.
• Figure 2: Double-line notation.
• Figure 3: Vertices in double-line notation.
• Figure 4: Gluon self-energy diagram in double-line notation.
• Figure 5: Some planar diagrams.