String (In)Stability Issues with Broken Supersymmetry

Abstract

We review the main results of our investigations motivated by the tadpole potentials of ten--dimensional strings with broken supersymmetry. While these are at best partial indications, it is hard to resist the feeling that they do capture some lessons of String Theory. For example, these very tadpole potentials lead to weak-string-coupling cosmologies that appear to provide clues on the onset of the inflation from an initial fast roll. The transition, if accessible to us, would offer a natural explanation for the lack of power manifested by the CMB at large angular scales. In addition, the same tadpole potentials can drive spontaneous compactifications to lower--dimensional Minkowski spaces at corresponding length scales. Furthermore, the cosmological solutions exhibit an intriguing ``"instability of isotropy" that, if taken at face value, would point to an accidental origin of compactification. Finally, symmetric static \(AdS \times  S\) solutions driven by the tadpole potentials also exist, but they are unstable due to mixings induced by their internal fluxes. On the other hand, the original Dudas--Mourad solution is perturbatively stable, and we have gathered some detailed evidence that instabilities induced by internal fluxes can be held under control in a similar class of weak--coupling type-IIB compactifications to Minkowski space.