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General conditions for scale-invariant perturbations in an expanding universe

We investigate the general properties of expanding cosmological models which generate scale-invariant curvature perturbations in the presence of a variable speed of sound. We show that in an expanding universe, generation of a super-Hubble, nearly scale-invariant spectrum of perturbations over a range of wavelengths consistent with observation requires at least one of three conditions: (1) accelerating expansion, (2) a speed of sound faster than the speed of light, or (3) super-Planckian energy density.

preprint2011arXivOpen access
Ghazal GeshnizjaniWilliam H. KinneyAzadeh Moradinezhad Dizgah
astro-ph.CO
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Open access3 authors1 topic
Imported metadata coverageMissing code, dataset, citation and institution fields are tracked without dominating the paper.Details
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Ghazal GeshnizjaniWilliam H. KinneyAzadeh Moradinezhad Dizgah

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