On holography with ADE singularities
Sunjin Choi, Yuji Tachikawa
TL;DR
This work analyzes AdS/CFT for $ ext{N}=4$ $U(N)$ SYM on $S^3/9Γ$ with $9Γ$ an ADE subgroup of $SU(2)$, uncovering a large holonomy-induced vacuum degeneracy tied to an ADE bulk singularity. It argues that bulk topological degrees of freedom living on the ADE singularity are captured holographically by a three-dimensional pure Chern-Simons theory at level $N$ with gauge group $_G$ determined by $9Γ$ via the McKay correspondence, and extends this to class S theories of type $U(N)$ by relating the degeneracy to CS vacua on a Riemann surface and to affine representations at level $N$. The paper also analyzes how the electric and magnetic one-form symmetries of the 4d theories map to the one-form symmetry of the CS side, showing consistency of symmetry actions under the duality and S-duality via the CS $S$-matrix. By matching the vacuum structures across the duality, it provides a concrete holographic realization of topological degrees of freedom arising from ADE singularities and clarifies how higher-form symmetries are realized in holographic CS theories. These results illuminate the interplay between topology, ADE singularities, and higher-form symmetries in holography and suggest further checks in less supersymmetric settings and broader bulk geometries.
Abstract
We study aspects of the AdS/CFT correspondence for $\mathcal{N}=4$ $U(N)$ super Yang-Mills theory on $S^3/Γ$, where $Γ\subset SU(2)$ is a finite subgroup, leading to an ADE singularity in the bulk AdS geometry. We show that a large vacuum degeneracy arises from the choice of gauge holonomy on $S^3/Γ$. On the gravity side, we argue that the bulk ADE singularity supports topological degrees of freedom responsible for this degeneracy. We then provide a holographic derivation of a corresponding large vacuum degeneracy for class S theories of type $U(N)$, showing that these topological degrees of freedom admit an effective description in terms of a three-dimensional level-$N$ Chern-Simons theory, whose gauge group $\mathsf{G}$ is determined by $Γ$. Finally, we discuss how the one-form symmetries of the $\mathcal{N}=4$ super Yang-Mills theory are realized on the Chern-Simons theory side.
