Tunneling without bounce

Abstract

The false vacua of some potentials do not decay via Euclidean bounces. This typically happens for tunneling actions with a flat direction (in field configuration space) that is lifted by a perturbation into a sloping valley, pushing the bounce off to infinity. Using three different approaches we find a consistent picture for such decays. In the Euclidean approach the bottom of the action valley consists of a family of pseudobounces (field configurations with some key good properties of bounces except extremizing the action). The pseudobounce result is validated by minimizing a Wentzel-Kramers-Brillouin action in Minkowski space along appropriate paths in configuration space. Finally, the most natural approach uses the tunneling action method proposed recently with a simple modification of boundary conditions.