Gravitation and tunnelling: Subtleties of the thin-wall approximation   and rapid decays
  I provide some simple physical arguments that, once gravitation and some subtleties are taken into account, rather broad classes of potentials result in instantons which tunnel relatively rapidly between perturbatively stable minima. In particular, due to some previously unappreciated technical subtleties, the decay rates for instantons which may be well-described as thin-wall are much larger than the usual Coleman-de Luccia result. I discuss with some level of rigor when the thin-wall approximation holds and clarify some misconceptions regarding the application of this approximation and its meaning. I also point out potentials involving small differences between the maxima and minima generically decay relatively rapidly. These two classes of potentials include those usually used to argue for the existence of a string landscape and in light of these results it is not clear that de Sitter vacua presently understood will generically be cosmologically long-lived. 
Keith Copsey
gr-qc hep-th