Non-BPS Branes in a Type I Orbifold

TL;DR

This paper investigates the spectrum and stability of non-BPS branes in a type I orbifold, revealing stable non-BPS D-particles and D-instantons with specific charge properties.

Contribution

It provides a detailed analysis of non-BPS branes in a type I orbifold, including their spectrum, charges, and stability, using covariant boundary state methods.

Findings

Identifies $ ext{Z}_2$- and $ ext{Z}$-charged non-BPS branes.

Finds stable non-BPS D-particle and D-instanton in the orbifold.

D-instanton can carry twisted R-R charge.

Abstract

We analyse the spectrum of non-BPS branes in the type I theory on the orbifold $T^4/{\cal I}_4$. We present a detailed analysis of the action of the worldsheet parity $\Omega$ on the different D-brane boundary state sectors of type IIB on $T^4/{\cal I}_4$, using the covariant formulation. Using these results we derive the spectrum of branes in the type I orbifold. We find $\Z_2$- and $\Z$- charged non-BPS branes. A study of the stability of these branes in the type I orbifold is also presented. We find that the type I non-BPS D-particle and D-instanton remain stable in the orbifold. The D-particle carries no charge whereas the non-BPS D-instanton can carry twisted R-R charge.