# Quantum stability in open string theory with broken supersymmetry

## TL;DR

This paper analyzes the 1-loop effective potential in type I string theory with broken supersymmetry, revealing conditions for local minima and the behavior of moduli and branes in compactified dimensions.

## Contribution

It demonstrates the existence of local minima of the effective potential with broken supersymmetry in dimensions up to five, and explores the dynamics of open and closed string moduli.

## Key findings

- Local minima of the potential can have arbitrary sign in d<=5.
- Closed string moduli are flat directions, while open string Wilson lines are massive.
- In T-dual backgrounds, brane positions are fixed, reducing gauge group rank.

## Abstract

We consider the 1-loop effective potential in type I string theory compactified on a torus, with supersymmetry broken by the Scherk-Schwarz mechanism. At fixed supersymmetry breaking scale M, and up to exponentially suppressed terms, we show that the potential admits local minima of arbitrary sign, in dimension d<=5. While the open string Wilson lines are massive, the closed string moduli are flat directions. In a T-dual picture, the relevant backgrounds involve isolated 1/2-branes, whose positions are frozen on orientifold planes, thus decreasing the rank of the gauge group, and introducing massless fermions in fundamental representations.