Threshold corrections in heterotic flux compactifications

TL;DR

This paper calculates one-loop threshold corrections to gauge and gravitational couplings in a broad class of heterotic flux compactifications, revealing their dependence on topological data and instanton effects.

Contribution

It provides the first detailed computation of threshold corrections in non-Kähler heterotic compactifications with flux, including non-perturbative instanton effects.

Findings

Threshold corrections depend on topological data of the bundle.

Worldsheet instantons contribute non-perturbative corrections.

Results connect heterotic and type I flux compactifications via S-duality.

Abstract

We compute the one-loop threshold corrections to the gauge and gravitational couplings for a large class of N=2 non-K\"ahler heterotic compactifications with three-form flux, consisting in principal two-torus bundles over K3 surfaces. We obtain the results as sums of BPS-states contributions, depending on the topological data of the bundle. We analyse also the worldsheet non-perturbative corrections coming from instantons wrapping the torus fiber, that are mapped under S-duality to D-instanton corrections in type I flux compactifications.