Clarifying perturbations in the ekpyrotic universe

Abstract

In this note I try to clarify the problem of perturbations in the ekpyrotic universe. I write down the most general matching conditions and specify the choices taken by the two debating sides. I also bring up the problem of surface stresses which always have to be present when a transition from a collapsing to an expanding phase is made.

3 pages, no figures Some typo's and a conceptial mistake corrected. Conclusions unaltered