Non-BPS D-branes and enhanced symmetry in an asymmetric orbifold

TL;DR

This paper explores the properties and stability of non-BPS D-branes in a nine-dimensional asymmetric orbifold, revealing gauge symmetry enhancement at a critical radius and relating different brane types through bulk symmetry transformations.

Contribution

It introduces a detailed analysis of non-BPS D-branes in an asymmetric orbifold, including boundary state construction at symmetry enhancement points and S-dual theory implications.

Findings

Two types of non-BPS D-branes are stable in different radius regimes.

At R=2, gauge symmetry is enhanced and branes are related by a bulk symmetry.

Boundary states are constructed using a free fermion representation.

Abstract

In this paper properties of D branes in a nine dimensional asymmetric orbifold are discussed, using a $(-1)^{F_L}\sigma_{1/2}$ projection, where $F_L$ is the leftmoving space-time fermion number and $\sigma_{1/2}$ is a freely acting shift of order two. There are two types of non BPS D branes, which are stable at $R>2$ and $R<2$ respectively. At R=2 there is a perturbative enhancement of gauge symmetry and the two types of branes are related by a global bulk symmetry transformation. At this point in the moduli space the associated boundary states are constructed using a free fermion representation of the theory. Some aspects of the enhancement of gauge symmetry in the S-dual type $\tilde I$ theory are discussed.