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arXiv · 1107.1241

General conditions for scale-invariant perturbations in an expanding universe

Ghazal Geshnizjani·William H. Kinney·Azadeh Moradinezhad Dizgah
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Abstract

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.

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Ghazal Geshnizjani, William H. Kinney, Azadeh Moradinezhad Dizgah. 2011-07-06. General conditions for scale-invariant perturbations in an expanding universe. https://doi.org/10.1088/1475-7516%2F2011%2F11%2F049

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