S-duality, boundary states, and higher-form symmetries on ALE spaces
The paper studies Abelian S-duality for Maxwell theory on A-type ALE spaces. It shows the path integral decomposes into theta-function blocks representing boundary states, leading to vector-valued modular covariance instead of standard modularity. Gluing two ALE spaces yields the partition function for $S^2 imes S^2$, and incorporating electric/magnetic 1-form symmetries reveals how these blocks behave as sections of line bundles.