Scale Invariance without Inflation?

Abstract

We propose a new alternative mechanism to seed a scale invariant spectrum of primordial density perturbations that does not rely on inflation. In our scenario, a perfect fluid dominates the early stages of an expanding, non-inflating universe. Because the speed of sound of the fluid decays, perturbations are left frozen behind the sound horizon, with a spectral index that depends on the fluid equation of state. We explore here a toy model that realizes this idea. Although the model can explain an adiabatic, Gaussian, scale invariant spectrum of primordial perturbations, it turns out that in its simplest form it cannot account for the observed amplitude of the primordial density perturbations.

6 two-column pages, 1 figure. Uses RevTeX4. v2: References added and number of required e-folds refined

References in corpus (5)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• An Alternative to Inflation
• Conditions for Generating Scale-Invariant Density Perturbations
• Inflationary Theory and Alternative Cosmology
• Running of the Scalar Spectral Index from Inflationary Models

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• Refining inflation using non-canonical scalars
• Simple Bounds from the Perturbative Regime of Inflation
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• Adiabatic regularization of power spectrum in nonminimally coupled general single-field inflation
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• Horizon-preserving dualities and perturbations in non-canonical scalar field cosmologies
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