Nonsingular perturbations in a bouncing brane model

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Abstract
The question of how perturbations evolve through a bounce in the Cyclic and Ekpyrotic models of the Universe remains a topical one. Issues concerning singularities at the background level and at the level of perturbation theory continue to be a matter of debate. In this report we hope to demonstrate a nonsingular collision between the boundary branes at the background level, and circumstances under which all perturbation variables remain bounded through the collision. As expected, we find most collisions to be singular even in the full 5D formalism, where first order perturbation theory breaks down for at least one perturbation variable. Only in the case that the boundary branes approach each other with constant velocity shortly before the bounce, can a consistent, nonsingular solution be found. It is then possible to follow the perturbations explicitly until the actual collision. In this case, we find that if a scale-invariant spectrum developed on the hidden brane, it will get transferred to the visible brane during the bounce.

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