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

TL;DR

This paper develops rules for constructing non-supersymmetric type IIB orientifold models with brane-antibrane systems that are free of tachyons, enabling stable, anomaly-free, and potentially phenomenologically relevant string compactifications.

Contribution

It introduces a systematic method to build tachyon-free, non-supersymmetric orientifolds with brane-antibrane configurations, including explicit six- and four-dimensional models.

Findings

Constructed anomaly-free, tachyon-free six-dimensional models with D9-branes and anti-D5-branes.

Developed four-dimensional chiral models with broken supersymmetry in some sectors.

Discussed moduli stabilization dynamics from brane-antibrane forces and cosmological constant effects.

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.