Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-07-06
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
4 pages, RevTeX
Scientific paper
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.
Dizgah Azadeh Moradinezhad
Geshnizjani Ghazal
Kinney William H.
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