D-instanton Induced Superpotential

TL;DR

This paper uses string field theory to determine the normalization of D-instanton contributions to the superpotential in type II string compactifications, focusing on O(1) instantons and their zero modes, and discusses multi-instanton effects.

Contribution

It provides a string field theory-based calculation of D-instanton superpotential corrections and analyzes multi-instanton contributions in flux-free backgrounds.

Findings

D-instanton corrections are fixed by string field theory methods.

Multi-instanton contributions vanish without background fluxes.

The analysis applies to generic superconformal field theories.

Abstract

We use string field theory to fix the normalization of the D-instanton corrections to the superpotential involving the moduli fields of type II string theory compactified on an orientifold of a Calabi-Yau threefold in the absence of fluxes. We focus on $O(1)$ instantons whose only zero modes are the four bosonic modes associated with translation of the instanton in non-compact directions and a pair of fermionic zero modes associated with the two supercharges broken by the instanton. We work with a generic superconformal field theory and express our answer in terms of the spectrum of open strings on the instanton. We analyse the contribution of multi-instantons of this kind to the superpotential and argue that it vanishes when background fluxes are absent.