Dirichlet Branes on Orientifolds

TL;DR

This paper classifies stable BPS and non-BPS D-branes in specific orientifold models, analyzing their stability, decay, and charge properties, and discusses the mathematical framework needed to describe them.

Contribution

It constructs all stable D-branes in the GP and DPBZ orientifolds and explores their stability regions and decay channels, revealing the relevance of twisted K-theory.

Findings

Identification of various stable non-BPS D-branes with torsion charge

Discovery of projective representations of the orientifold GSO group

Revelation that twisted K-theory is relevant for GP orientifold

Abstract

We consider the classification of BPS and non-BPS D-branes in orientifold models. In particular we construct all stable BPS and non-BPS D-branes in the Gimon-Polchinski (GP) and Dabholkar-Park-Blum-Zaffaroni (DPBZ) orientifolds and determine their stability regions in moduli space as well as decay products. We find several kinds of integrally and torsion charged non-BPS D-branes. Certain of these are found to have projective representations of the orientifold $\times$ GSO group on the Chan-Paton factors. It is found that the GP orientifold is not described by equivariant orthogonal K-theory as may have been at first expected. Instead a twisted version of this K-theory is expected to be relevant.