5d gauge theories on orbifolds and 4d 't Hooft line indices

Abstract: We study indices for 5d gauge theories on S^1 \times S^4/Z_n. In the large orbifold limit, n \rightarrow \infty, we find evidence that the indices become 4d indices in the presence of a 't Hooft line operator. The non-perturbative part of the index poses some subtleties when being compared to the 4d monopole bubbling which happens in the presence of 't Hooft line operators. We study such monopole bubbling indices and find an interesting connection to the Hilbert series of the moduli space of instantons on an auxiliary ALE space.