Code construction and ensemble holography of simply-laced WZW models at level 1

Abstract: We introduce a code construction for Wess-Zumino-Witten (WZW) models associated with simply-laced affine Lie algebras at level 1. The chiral primary fields of these rational CFTs can be parametrized by the elements of the outer automorphism group of the affine algebra, which is isomorphic to the discriminant group $G$ of the root lattice. We show that the classification of even, self-dual codes over the alphabet $G$ is equivalent to the classification of modular-invariant CFTs. Each individual CFT is dual to a Chern-Simons theory, after gauging the maximal, non-anomalous subgroup of its $1$-form symmetry group specified by the code. We calculate the ensemble average of these CFTs, which is holographically dual to ``CS gravity"-- where the bulk theory is summed over topologies. When the alphabet $G$ consists only of elements of square-free order, we explicitly show that this ensemble average reproduces the Poincar\'e series of the vacuum character, which can be interpreted as the CS path-integral summed only over handlebody topologies. However, when $G$ contains elements of non-square-free order, additional contributions from singular topologies arise.