D-instanton Induced Superpotential

Understand

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.