Partition functions and fibering operators on the Coulomb branch of 5d SCFTs

We study 5d N = 1 supersymmetric field theories on closed five-manifolds M-5 which are principal circle bundles over simply-connected Kahler four-manifolds, M-4, equipped with the Donaldson-Witten twist. We propose a new approach to compute the sup ersymmetric partition function on M-5 through the insertion of a fibering operator, which introduces a non-trivial fibration over M-4, in the 4d topologically twisted field theory. We determine the so-called Coulomb branch partition function on any such M-5, which is conjectured to be the holomorphic 'integrand' of the full partition function. We precisely match the low-energy effective field theory approach to explicit one-loop computations, and we discuss the effect of non-perturbative 5d BPS particles in this context. When M-4 is toric, we also reconstruct our Coulomb branch partition function by appropriately gluing Nekrasov partition functions. As a by-product of our analysis, we provide strong new evidence for the validity of the Lockhart-Vafa formula for the five-sphere partition function.

Automated summary

We propose a new approach to computing the supersymmetric partition function on closed five-manifolds by introducing a non-trivial fibration over the four-manifold and examining the Coulomb branch partition function. We match the low-energy effective field theory approach to explicit one-loop computations and discuss the effects of non-perturbative particles. We also provide evidence for the validity of the Lockhart-Vafa formula for the five-sphere partition function.