String Theory seminar - Ivano Basile Seminar

Abstract: We discuss the existence and stability of vacua in string theories where supersymmetry is either absent or broken at the string scale. In particular we present no-go results regarding de Sitter compactifications, connecting them to some Swampland conjectures, thereby focusing on anti-de Sitter (AdS) flux vacua arising from the USp(32) and U(32) orientifold models and from the SO(16) x SO(16) heterotic model. We investigate perturbative and non-perturbative instabilities and frame the vacua in terms of brane stacks, analyzing their back-reacted geometry and reproducing AdS in the near-horizon limit. Then we describe the instabilities as branes separating from the stack, computing the associated decay rate matching a probe brane computation to the gravitational result. We conclude briefly discussing possible implications regarding the fate of unstable vacua in string theory beyond the semi-classical limit, connecting this scenario to the Weak Gravity Conjecture, holographic renormalization group flows and to a "de Sitter on a brane" construction that was outlined in the recent literature.