Notes on unoriented D-brane instantons

TL;DR

This paper explores various aspects of unoriented D-brane instantons, including their role in non-perturbative effects and threshold corrections in string theory, with a focus on their mathematical and physical properties.

Contribution

It provides a detailed analysis of unoriented D-brane instantons and their contributions to superpotentials and threshold corrections, offering new insights into non-perturbative string effects.

Findings

Threshold corrections to BPS-saturated couplings analyzed.

Non-perturbative superpotentials from gauge and exotic instantons discussed.

Multi D-string instanton interpretation provided.

Abstract

In the first lecture, we discuss basic aspects of worldsheet and penta-brane instantons as well as (unoriented) D-brane instantons, which is our main focus here, and threshold corrections to BPS-saturated couplings. The second lecture is devoted to non-perturbative superpotentials generated by `gauge' and `exotic' instantons living on D3-branes at orientifold singularities. In the third lecture we discuss the interplay between worldsheet and D-string instantons on $T^4/Z_2$. We focus on a 4-fermi amplitude, give Heterotic and perturbative Type I descriptions, and offer a multi D-string instanton interpretation. We conclude with possible interesting developments.