String instantons, fluxes and moduli stabilization

TL;DR

The work constructs and analyzes dual pairs of heterotic and Type I string models based on freely-acting $\mathbb{Z}_2 \times \mathbb{Z}_2$ orbifolds, showing how perturbative heterotic data can yield exact non-perturbative Type I gauge-threshold corrections via the adiabatic argument. By combining Euclidean brane instantons ($E5$ and $E1$) with closed-string fluxes (RR, NSNS, and metric fluxes), the authors demonstrate racetrack-type moduli stabilization that can also fix the dilaton in a controlled setting, with explicit expressions for threshold corrections, instanton zero modes, and flux-induced superpotentials. The analysis provides concrete links between gauge dynamics (gaugino condensation, SQCD-like sectors) and moduli stabilization in a class of smooth Calabi–Yau-like geometries, highlighting how twisted-torus fluxes and orbifold images affect the non-perturbative landscape. The results offer a tractable arena to study the interplay of fluxes, instantons, and duality, with potential implications for constructing stabilized vacua in realistic string compactifications and for understanding the role of non-perturbative effects in moduli stabilization.

Abstract

We analyze a class of dual pairs of heterotic and type I models based on freely-acting $\mathbb{Z}_2 \times \mathbb{Z}_2$ orbifolds in four dimensions. Using the adiabatic argument, it is possible to calculate non-perturbative contributions to the gauge coupling threshold corrections on the type I side by exploiting perturbative calculations on the heterotic side, without the drawbacks due to twisted moduli. The instanton effects can then be combined with closed-string fluxes to stabilize most of the moduli fields of the internal manifold, and also the dilaton, in a racetrack realization of the type I model.