Mass scales, supersymmetry breaking and open strings

TL;DR

This paper reviews string vacua with large internal volumes or low string scales, focusing on supersymmetry breaking mechanisms like Scherk-Schwarz deformations and brane supersymmetry breaking in type I models.

Contribution

It provides a comprehensive overview of supersymmetry breaking in string models, highlighting the role of branes and internal volume effects.

Findings

Scherk-Schwarz deformations can break supersymmetry in type I models.

Brane supersymmetry breaking occurs when tadpole conditions require supersymmetry to be broken on certain branes.

Supersymmetry can be broken at the string scale on branes while remaining intact in the bulk.

Abstract

We review physical motivations and possible realizations of string vacua with large internal volume and/or low string scale and discuss the issue of supersymmetry breaking. In particular, we describe the key features of Scherk-Schwarz deformations in type I models and conclude by reviewing the phenomenon of ``brane supersymmetry breaking'': the tadpole conditions of some type-I models require that supersymmetry be {\it broken at the string scale} on a collection of branes, while being exact, to lowest order, in the bulk and on other branes.