Open string models with Scherk-Schwarz SUSY breaking and localized anomalies

TL;DR

This paper explores chiral four-dimensional IIB orientifold models with Scherk-Schwarz supersymmetry breaking, focusing on anomaly cancellation mechanisms involving twisted Ramond-Ramond fields and the implications for gauge symmetry breaking.

Contribution

It constructs new orientifold models with Scherk-Schwarz SUSY breaking and provides a geometric analysis of anomaly cancellation via a generalized Green--Schwarz mechanism.

Findings

Anomaly cancellation involves twisted Ramond-Ramond axions and 4-forms.

New Z3xZ3' model with only D9-branes is constructed.

The number of broken U(1) gauge fields exceeds four-dimensional expectations.

Abstract

We study examples of chiral four-dimensional IIB orientifolds with Scherk--Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z3xZ3' model, containing only D9-branes, and rederive from a more geometric perspective the known Z6'xZ2' model, containing D9, D5 and \bar D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green--Schwarz mechanism involving twisted Ramond--Ramond axions and 4-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view. We also point out that the number of spontaneously broken U(1) gauge fields is in general greater than what expected from a four-dimensional analysis of anomalies.