Semi-infinite slow contraction (ε>3) eliminates particle horizons, asymptotes to Minkowski in the past, remains geodesically complete and BGV-evading, and supplies stable low-entropy initial conditions after a non-singular bounce.
Scale-invariant perturbations in ekpyrotic cosmologies without fine-tuning of initial conditions
2 Pith papers cite this work, alongside 46 external citations. Polarity classification is still indexing.
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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 super-horizon perturbations that seed structure in the post-bounce universe. An analysis by Tolley and Wesley (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.
years
2026 2representative citing papers
Refines two-field DHOST bouncing model to match observed f_NL and keep strong-coupling scale above background energy, claiming full viability at linear and non-linear levels.
citing papers explorer
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Causal Horizons, Geodesic Completeness and Stability in Slow Contraction Cosmology
Semi-infinite slow contraction (ε>3) eliminates particle horizons, asymptotes to Minkowski in the past, remains geodesically complete and BGV-evading, and supplies stable low-entropy initial conditions after a non-singular bounce.
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Non-Gaussianity and Strong-Coupling Problem in a Two-Field DHOST Bouncing Model
Refines two-field DHOST bouncing model to match observed f_NL and keep strong-coupling scale above background energy, claiming full viability at linear and non-linear levels.