Exotic instanton counting and heterotic/type I' duality

TL;DR

This paper calculates the non-perturbative contributions to gauge couplings from exotic instantons in Type I' string theory and confirms their agreement with dual heterotic theory predictions, testing string duality.

Contribution

It provides a novel computation of exotic instanton effects in Type I' theory and verifies their consistency with heterotic duality through exact matching.

Findings

Exact localization of the instanton partition function.

Matching of non-perturbative corrections with heterotic dual results.

Validation of the exotic instanton effects in string duality.

Abstract

We compute the partition function for the exotic instanton system corresponding to D-instantons on D7 branes in Type I' theory. We exploit the BRST structure of the moduli action and its deformation by RR background to fully localize the integration. The resulting prepotential describes non-perturbative corrections to the quartic couplings of the gauge field F living on the D7's. The results match perfectly those obtained in the dual heterotic theory from a protected 1-loop computation, thus providing a non-trivial test of the duality itself.