Discrete moduli for Type I compactifications

TL;DR

This paper investigates discrete moduli in Type I string compactifications on a 4-torus, revealing how non-trivial RR 4-form backgrounds relate to Spin(32)/Z_2 bundles and holonomies, with implications for orientifold variants.

Contribution

It introduces a novel connection between discrete RR 4-form backgrounds and Spin(32)/Z_2 bundle holonomies in Type I compactifications.

Findings

Non-trivial RR 4-form backgrounds correspond to specific Spin(32)/Z_2 bundles.

Holonomies form a quadruple that characterizes the bundle topology.

Discussion of other discrete moduli and orientifold variants.

Abstract

We study type I compactification on a 4-torus, with a non-trivial discrete background RR 4-form field. By using string dualities and recent insights for gauge theories on tori, we find that a non-trivial background for the RR 4-form is correlated with Spin(32)/Z_2 bundles that are described by a ``non-trivial quadruple'' of holonomies. We also briefly discuss other discrete moduli for the type I string, and variants of orientifold planes.