Volume independence in large Nc QCD-like gauge theories

TL;DR

This paper explores how large Nc gauge theories exhibit volume independence, linking different theories through orbifold and orientifold equivalences, which could simplify studying QCD-like theories in various volume regimes.

Contribution

It demonstrates the conditions under which volume independence holds in large Nc gauge theories, establishing new equivalences between different QCD-like theories across volume scales.

Findings

Volume independence fails below a critical size due to symmetry breaking.

QCD(Adj) maintains volume independence down to arbitrarily small sizes.

A large Nc orientifold equivalence connects QCD(AS) and QCD(Adj) in different volume regimes.

Abstract

Volume independence in large $\Nc$ gauge theories may be viewed as a generalized orbifold equivalence. The reduction to zero volume (or Eguchi-Kawai reduction) is a special case of this equivalence. So is temperature independence in confining phases. In pure Yang-Mills theory, the failure of volume independence for sufficiently small volumes (at weak coupling) due to spontaneous breaking of center symmetry, together with its validity above a critical size, nicely illustrate the symmetry realization conditions which are both necessary and sufficient for large $\Nc$ orbifold equivalence. The existence of a minimal size below which volume independence fails also applies to Yang-Mills theory with antisymmetric representation fermions [QCD(AS)]. However, in Yang-Mills theory with adjoint representation fermions [QCD(Adj)], endowed with periodic boundary conditions, volume independence remains valid down to arbitrarily small size. In sufficiently large volumes, QCD(Adj) and QCD(AS) have a large $\Nc$ ``orientifold'' equivalence, provided charge conjugation symmetry is unbroken in the latter theory. Therefore, via a combined orbifold-orientifold mapping, a well-defined large $\Nc$ equivalence exists between QCD(AS) in large, or infinite, volume and QCD(Adj) in arbitrarily small volume. Since asymptotically free gauge theories, such as QCD(Adj), are much easier to study (analytically or numerically) in small volume, this equivalence should allow greater understanding of large $\Nc$ QCD in infinite volume.