2007
DOI: 10.1088/1475-7516/2007/05/006
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Scale invariance in expanding and contracting universes from two-field models

Abstract: We study cosmological perturbations produced by the most general twoderivative actions involving two scalar fields, coupled to Einstein gravity, with an arbitrary field space metric, that admit scaling solutions. For expanding universes, we find that scaleinvariant adiabatic perturbation spectra can be produced for any equation of state parameter w that satisfies −1 ≤ w < −1/3, and that all the scaling solutions are attractors. For contracting universes, we show that scale-invariant adiabatic perturbations can… Show more

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Cited by 58 publications
(97 citation statements)
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References 68 publications
(118 reference statements)
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“…The Friedmann equations leads to a power law contraction a ∝ (−t) p with p ≡ 2/c 2 1. From here onwards, we follow [163] (see also [412]) and switch back to conformal time η = a −1 dt so that…”
Section: Basics Of Cosmological Perturbation Theorymentioning
confidence: 99%
“…The Friedmann equations leads to a power law contraction a ∝ (−t) p with p ≡ 2/c 2 1. From here onwards, we follow [163] (see also [412]) and switch back to conformal time η = a −1 dt so that…”
Section: Basics Of Cosmological Perturbation Theorymentioning
confidence: 99%
“…[26] that the scaling radiation/matter eras can be followed by the assisted inflationary attractor. However, this analysis does not cover the models in which the multiple scalar fields are coupled each other [28][29][30].…”
Section: Introductionmentioning
confidence: 99%
“…The mechanism relies on having two scalar fields (e.g., the radion and the Calabi-Yau dilaton [9]) each obtain scale-invariant fluctuations by evolving down a steep potential V (φ 1 , φ 2 ) during the ekpyrotic phase, with one linear combination forming a spectrum of time-delay fluctuations and the second a spectrum of entropic perturbations. The latter are converted to curvature fluctuations if the two-field trajectory bends or bounces as the universe approaches the big crunch, which occurs generically.An essential feature of the entropic mechanism is that the classical ekpyrotic trajectory along V (φ 1 , φ 2 ) is unstable to transverse fluctuations [9,10,12,13]. A consequence is that, without adding some mechanism to force the universe to begin very close to the classical track [13], an overwhelming fraction of the universe fails to make it all the down the classical trajectory simply due to quantum fluctuations.…”
mentioning
confidence: 99%
“…An essential feature of the entropic mechanism is that the classical ekpyrotic trajectory along V (φ 1 , φ 2 ) is unstable to transverse fluctuations [9,10,12,13]. A consequence is that, without adding some mechanism to force the universe to begin very close to the classical track [13], an overwhelming fraction of the universe fails to make it all the down the classical trajectory simply due to quantum fluctuations.…”
mentioning
confidence: 99%
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