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arXiv · hep-ph/0106153

The primordial curvature perturbation in the ekpyrotic Universe

David H. Lyth
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Abstract

In the ekpyrotic scenario the Universe is initially collapsing, the energy density coming from a scalar field with a negative exponential potential. On the basis of a calculation ignoring the gravitational back-reaction the authors of the scenario claim that during collapse the vacuum fluctuation creates a perturbation in the comoving curvature, which has a flat spectrum in accordance with observation. In this note the back-reaction is included, and it is found that the spectrum during collapse is strongly scale-dependent with negligible magnitude. The spectrum is continuous across the bounce if the spacetime is smooth, making it unlikely that the ekpyrotic scenario can be compatible with observation.

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David H. Lyth. 2001-08-19. The primordial curvature perturbation in the ekpyrotic Universe. https://doi.org/10.1016/s0370-2693(01)01374-0

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