D-brane Spectrum and K-theory Constraints of D=4, N=1 Orientifolds

TL;DR

This paper analyzes the spectrum of D-branes in specific orientifold models, computes their K-theory charges directly from conformal field theory, and discusses implications for string model building and stability.

Contribution

It provides a direct CFT computation of K-theory torsion charges in D=4, N=1 orientifolds, offering new constraints for string model construction.

Findings

K-theory torsion charges computed directly from CFT

Non-trivial constraints on string model building

Identification of stability regions for non-BPS D-branes

Abstract

We study the spectrum of stable BPS and non-BPS D-branes in Z_2 x Z_2 orientifolds for all choices of discrete torsion between the orbifold and orientifold generators. We compute the torsion K-theory charges in these D=4, N=1 orientifold models directly from worldsheet conformal field theory, and compare with the K-theory constraints obtained indirectly using D-brane probes. The K-theory torsion charges derived here provide non-trivial constraints on string model building. We also discuss regions of stability for non-BPS D-branes in these examples.