Non-supersymmetric string theories: duality, stability, and phase structure

Most recent developments in string duality have focused on string theories with spacetime supersymmetry. However, it has not been known whether string duality is a more general phenomenon, and might hold even without supersymmetry. In this talk, I discuss the methods that can be used for extending duality beyond supersymmetry, and I present the first known examples of strong/weak coupling duality relations between non-supersymmetric tachyon-free string theories. I largely focus on the case of the tachyon-free SO(16)*SO(16) string, but I also consider additional string models as well. Using these duals, I then propose a phase diagram describing the stability of these strings as functions of their couplings and radii. Finally, I show how these techniques can even be used in a supersymmetric setting in order to realize a new continuous connection between the Type I string and M-theory. This talk reports on work performed in collaboration with Julie Blum. (7 refs).