Nearly scale-invariant curvature modes from entropy perturbations during graceful exit

Abstract

In this Letter, we describe how a spectrum of entropic perturbations generated during a period of slow contraction can source a nearly scale-invariant spectrum of curvature perturbations on length scales larger than the Hubble radius during the transition from slow contraction to a classical non-singular bounce (the `graceful exit' phase). The sourcing occurs naturally through higher-order scalar field kinetic terms common to classical (non-singular) bounce mechanisms. We present a concrete example in which, by the end of the graceful exit phase, the initial entropic fluctuations have become negligible and the curvature fluctuations have a nearly scale-invariant spectrum with an amplitude consistent with observations.

arXiv comment6 pages, 2 figures

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• Dynamical attractors in contracting spacetimes dominated by kinetically coupled scalar fields
• Fingerprints of a Non-Inflationary Universe from Massive Fields
• Cuscuton Bounce Beyond the Linear Regime: Bispectrum and Strong Coupling Constraints
• Notes on the post-bounce background dynamics in bouncing cosmologies
• Torsion, Gravity Induced Chiral Symmetry Breaking and Cosmological Bounce
• Probability of the Initial Conditions for Inflation and Slow Contraction
• Kinetically-driven ekpyrosis