Heterotic / type I duality and D-brane instantons

TL;DR

This paper explores heterotic/type I duality in 8 and 9 dimensions, analyzing non-perturbative effects and D-brane instantons through effective action terms and string calculations.

Contribution

It provides a detailed comparison of heterotic and type I string theories, including instanton corrections and higher-order perturbative contributions, enhancing understanding of duality.

Findings

Agreement between heterotic one-loop and type I tree-level calculations.

Identification of heterotic world-sheet instanton corrections as D-brane instantons.

Insights into non-perturbative effects in string dualities.

Abstract

We study heterotic/type I duality in d=8,9 uncompactified dimensions. We consider the special (``BPS saturated'') F^4 and R^4 terms in the effective one-loop heterotic action, which are expected to be non-perturbatively exact. Under the standard duality map these translate to tree-level, perturbative and non-perturbative contributions on the type I side. We check agreement with the one-loop open string calculation, and discuss the higher-order perturbative contributions, which arise because of the mild non-holomorphicities of the heterotic elliptic genus. We put the heterotic world-sheet instanton corrections in a form that can be motivated as arising from a D-brane instanton calculation on the type-I side.