# High Energy Theory Seminar

*,*Harvard University

*,*

https://caltech.zoom.us/j/795527605 Meeting ID 795 527 605

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 robust 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. The latter is often the case with SUSY-preserving boundary conditions. I will explain how to understand the topological obstruction in detail using bordism, which will show that it is very 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 (SUSY-compatible) spin structure. There is a dynamical obstruction due to a positive energy theorem which is circumvented by higher-derivative corrections. Our model can be embedded in string theory. Our techniques can be used to construct a plethora of bubbles of nothing for spaces of interest like CY6's, G2 manifolds, or Sasaki-Einstein manifolds. We will explain how to study and circumvent the topological and dynamical obstruction in these cases. Avoiding the dynamical obstruction means avoiding a modified energy condition which might be related to the Weak Gravity Conjecture. Our results lend support to the conjecture that any non-supersymmetric vacuum of quantum gravity is ultimately unstable.