On ekpyrotic brane collisions

TL;DR

This paper derives five-dimensional metrics for non-singular brane collisions in the ekpyrotic scenario, revealing constraints on matter properties and the limitations of four-dimensional effective theories.

Contribution

It provides explicit five-dimensional solutions for brane collisions considering brane tension, highlighting the negative energy density requirement and the limitations of 4D descriptions.

Findings

Brane collisions can be described by specific 5D metrics.

Matter created in collisions must have negative energy density or pressure.

Collapse of the fifth dimension is an artifact of 4D effective theory.

Abstract

We derive the five-dimensional metrics which describe a non-singular boundary brane collision in the ekpyrotic scenario in the context of general relativity, taking into account brane tension. We show that the metrics constrain matter created in the collision to have negative energy density or pressure. In particular, the minimal field content of heterotic M-theory leads to negative energy density. We also consider bulk brane-boundary brane collisions and show that the collapse of the fifth dimension is an artifact of the four-dimensional effective theory.