Orientifolds of String Theory Melvin backgrounds

TL;DR

This paper explores the construction and analysis of orientifold models in string theory on Melvin backgrounds, revealing novel D-brane and O-plane configurations, supersymmetry properties, and boundary state formulations.

Contribution

It introduces two new classes of orientifold models on Melvin backgrounds with unique D-brane/O-plane configurations and supersymmetry features.

Findings

D-branes and O-planes can be smeared or rotated in Melvin backgrounds.

Supersymmetry can be partially restored with multiple Melvin spaces.

Boundary and crosscap states are explicitly constructed.

Abstract

We study the dynamics of type I strings on Melvin backgrounds, with a single or multiple twisted two-planes. We construct two inequivalent types of orientifold models that correspond to (non-compact) irrational versions of Scherk-Schwarz type breaking of supersymmetry. In the first class of vacua, D-branes and O-planes are no longer localized in space-time but are smeared along the compact Melvin coordinate with a characteristic profile. On the other hand, the second class of orientifolds involves O-planes and D-branes that are both rotated by an angle proportional to the twist. In case of ``multiple Melvin spaces'', some amount of supersymmetry is recovered if the planes are twisted appropriately and part of the original O-planes are transmuted into new ones. The corresponding boundary and crosscap states are determined.