Novel Type I Compactifications

TL;DR

The paper identifies two distinct classes of type I compactifications distinguished by a discrete 6-form potential, with implications for moduli and singularities, and explores analogous discrete choices in other string theories.

Contribution

It introduces a new classification of type I compactifications based on a discrete 6-form potential and discusses their properties and analogies in other string theories.

Findings

Two classes of type I compactifications distinguished by a discrete 6-form potential.

New class of compactifications has fewer moduli according to duality.

Discrete choices in other theories lead to spaces with frozen singularities.

Abstract

We argue that there are two distinct classes of type I compactification to four dimensions on any space. These two classes are distinguished in a mysterious way by the presence (or absence) of a discrete 6-form potential. In simple examples, duality suggests that the new class of compactifications have reduced numbers of moduli. We also point out analogous discrete choices in M, F and type II compactifications, including some with $G_2$ holonomy. These choices often result in spaces with frozen singularities.