New Instanton Effects in String Theory

TL;DR

This paper uncovers new instanton effects in string theory compactifications with N=1 supersymmetry, revealing their contributions to superpotentials and higher-derivative terms, especially in heterotic and Type IIA models.

Contribution

It introduces a new class of instanton effects that contribute to multi-fermion and higher-derivative F-terms, expanding understanding of non-perturbative effects in string compactifications.

Findings

Instantons can generate new multi-fermion F-terms.

Instantons deform the moduli space in heterotic compactifications.

New derivations of worldsheet instanton effects in Type IIA are provided.

Abstract

We describe a new class of instanton effects in string compactifications that preserve only N=1 supersymmetry in four dimensions. As is well-known, worldsheet or brane instantons in such a background can sometimes contribute to an effective superpotential for the moduli of the compactification. We generalize this phenomenon by showing that such instantons can also contribute to new multi-fermion and higher-derivative F-terms in the low-energy effective action. We consider in most detail the example of heterotic compactification on a Calabi-Yau threefold X with gauge bundle V, in which case we study worldsheet instanton effects that deform the complex structure of the moduli space associated to X and V. We also give new, slightly more economical derivations of some previous results about worldsheet instantons in Type IIA Calabi-Yau compactifications.