Tachyon-free Non-supersymmetric Type IIB Orientifolds via Brane-Antibrane Systems

TL;DR

This paper develops a comprehensive framework for constructing tachyon-free, non-supersymmetric Type IIB orientifolds by incorporating branes and antibranes in six- and four-dimensional compactifications. It provides general rules for open-string spectra, Chan-Paton embeddings, and RR tadpole cancellation, and demonstrates that open-string tachyons can be avoided by separating branes and antibranes or using projection techniques. The authors present explicit anomaly-free six-dimensional models and four-dimensional examples that feature coexisting supersymmetric brane sectors and non-supersymmetric hidden anti-brane sectors, offering mechanisms for SUSY breaking and mediation. They also discuss dynamical aspects such as non-cancelled brane–antibrane forces and a positive cosmological constant, which may influence moduli stabilization, and they highlight dualities linking these constructions to the non-supersymmetric USp(32) theory, enriching the landscape of string vacua with controlled SUSY breaking.

Abstract

We derive the rules to construct type IIB compact orientifolds in six and four dimensions including D-branes and anti-D-branes. Even though the models are non-supersymmetric due to the presence of the anti-D-branes, we show that it is easy to construct large classes of models free of tachyons. Brane-antibrane annihilation can be prevented for instance by considering models with branes and antibranes stuck at different fixed points in the compact space. We construct several anomaly-free and tachyon-free six-dimensional orientifolds containing D9-branes and anti-D5-branes. This setup allows to construct four-dimensional chiral models with supersymmetry unbroken in the bulk and in some D-brane sectors, whereas supersymmetry is broken (at the string scale) in some `hidden' anti-D-brane sector. We present several explicit models of this kind. We also comment on the role of the non-cancelled attractive brane-antibrane forces and the non-vanishing cosmological constant, as providing interesting dynamics for the geometric moduli and the dilaton, which may contribute to their stabilization.