Supersymmetry breaking, brane dynamics and the swampland

Abstract

Breaking supersymmetry in string theory entails a number of instabilities, both of perturbative and non-perturbative. This casts doubt on the consistency of string theory upon supersymmetry breaking, at least at the level of low-energy effective field dynamics. In order to explore this issue, in this contribution we review the connection between vacuum (in)stabilities and the interactions between branes of various dimensions, both charged and uncharged, in three models where supersymmetry is broken at the string scale. These are the $USp(32)$ and $U(32)$ orientifold projections of the type IIB and type $0$B strings and the $SO(16) \times SO(16)$ heterotic model. We describe the force exerted by branes in the probe regime and via a string amplitude computation. Whenever they can be compared, they show qualitative agreement despite no (manifest) supersymmetric protection takes place. We discuss a deeper connection with the weak gravity conjecture for charged branes, which is satisfied in a novel way due to a renormalization of the effective charge-to-tension ratio.