K3 Orientifolds

TL;DR

This paper constructs and analyzes orientifold models of Type IIB string theory on K3 surfaces, exploring their spectra, D-brane configurations, and dualities, including cases with purely closed string sectors.

Contribution

It generalizes previous Z_2 orientifold models to Z_N orbifolds, classifies models based on D-brane content, and relates these to heterotic string instantons.

Findings

Classification of orientifold models into two categories based on D-brane content.

Identification of models with purely closed string sectors.

Explicit spectra of six-dimensional N=1 supergravity theories.

Abstract

We study string theory propagating on R^6 times K3 by constructing orientifolds of Type IIB string theory compactified on the T^4/Z_N orbifold limits of the K3 surface. This generalises the Z_2 case studied previously. The orientifold models studied may be divided into two broad categories, sometimes related by T-duality. Models in category A require either both D5- and D9-branes, or only D9-branes, for consistency. Models in category B require either only D5-branes, or no D-branes at all. This latter case is an example of a consistent purely closed unoriented string theory. The spectra of the resulting six dimensional N=1 supergravity theories are presented. Precise statements are made about the relation of the Z_N ALE spaces and D5-branes to instantons in the dual heterotic string theory.