Strings and QCD?

TL;DR

Polchinski surveys multiple perspectives on whether large-$N$ QCD is equivalent to a string theory. From Regge phenomenology to lattice strong-coupling, two-dimensional gauge theory, and long-string analyses at low and high energy, he finds partial string-like features but fundamental mismatches (e.g., nonfree embedding coordinates, Liouville dynamics, and high-temperature degree-of-freedom growth) that challenge a simple equivalence. The work highlights that a viable string description may require a nontrivial continuum limit, effective-string constructions with induced metrics, or Dirichlet-boundary modifications rather than a naive Nambu–Goto/String–Liouville match. Overall, while explicit equivalence remains elusive, the survey identifies promising directions for reconciling string theory techniques with QCD physics and for guiding future investigations towards a refined string reinterpretation of large-$N$ QCD.

Abstract

Is large-$N$ QCD equivalent to a string theory? Maybe, maybe not. I review various attempts to answer the question.