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Scale-invariant perturbations in ekpyrotic cosmologies without fine-tuning of initial conditions

Author(s): Levy, Aaron M.; Ijjas, Anna; Steinhardt, Paul J.

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Abstract: Ekpyrotic bouncing cosmologies have been proposed as alternatives to inflation. In these scenarios, the Universe is smoothed and flattened during a period of slow contraction preceding the bounce while quantum fluctuations generate nearly scale-invariant superhorizon perturbations that seed structure in the post-bounce Universe. An analysis by Tolley andWesley (2007) showed that, for a wide range of ekpyrotic models, generating a scale-invariant spectrum of adiabatic or entropic fluctuations is only possible if the cosmological background is unstable, in which case the scenario is highly sensitive to initial conditions. In this paper, we analyze an important counterexample: a simple action that generates a Gaussian, scale-invariant spectrum of entropic perturbations during ekpyrotic contraction without requiring fine-tuned initial conditions. Based on this example, we discuss some generalizations.
Publication Date: 15-Sep-2015
Electronic Publication Date: 22-Sep-2015
Citation: Levy, Aaron M, Ijjas, Anna, Steinhardt, Paul J. (2015). Scale-invariant perturbations in ekpyrotic cosmologies without fine-tuning of initial conditions. PHYSICAL REVIEW D, 92, doi:10.1103/PhysRevD.92.063524
DOI: doi:10.1103/PhysRevD.92.063524
ISSN: 1550-7998
EISSN: 1550-2368
Type of Material: Journal Article
Journal/Proceeding Title: PHYSICAL REVIEW D
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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