Remote Nordic HET seminar: Irene Valenzuela

Speaker: Irene Valenzuela

Title: Nothing but bubbles

Abstract: A bubble of nothing is a spacetime instability where a compact dimension collapses. After nucleation, it expands at the speed of light, leaving "nothing" behind. There are a couple of mechanisms that can prevent the existence of a bubble: Either it is not energetically favourable to produce them, or there is a topological obstruction to their existence. We argue that both of them seem to be absent in string compactifications once supersymmetry is broken. I will explain how to understand the topological obstruction using bordism, which will show that it is generically absent even for a SUSY-compatible spin structure. As a proof of principle, we construct and embed in string theory an explicit bubble of nothing for a T3 with completely periodic spin structure. The dynamical obstruction, which relies on a certain local energy condition, is circumvented by higher-derivative corrections; and in the presence of fluxes, it seems related to the Weak Gravity Conjecture bound. Our techniques can be used to construct a plethora of new bubbles of nothing and lend support to the conjecture that any non-supersymmetric vacuum of quantum gravity is ultimately unstable.
If time allows, I will discuss further Swampland constraints on short-lived dS spaces decaying from one to the next through a cascade of non-perturbative nucleation of bubbles. These spaces are dual to effective theories of scalars rolling on potentials that do not allow for eternal inflation.