Towards degeneracy breaking of early universe models

Recently it has been shown that many of the puzzling features of conventional cosmological models (such as the horizon and flatness problems) could be explained by invoking inflationary models of the early universe with an exponential expansion phase at very early epochs. These models have the added advantage that they are able to make a definite prediction about the present matter density in the universe, i.e. they require that the density be exactly equal to the closure density which in turn can be easily estimated from the Hubble constant now known to within a factor of two. Now if one goes back to an earlier idea that explored the possibility of unusual clustering of quasar redshifts around z = 2 or 3, we get an example of another cosmological model with a definite prediction for the present overall matter density. This is a modified version of the Eddington-Lemaitre type of model which naturally accommodates such features as a clustering of quasars at certain epochs. From these models one can get a prediction for the present matter density which would be an involved function of the Hubble constant and the redshifts at which such clustering occurs. It can be shown that if such clustering had occurred at any z, the present matter density predicted would be substantially smaller than the corresponding closure density. The conclusion is that any clustering of quasar redshifts is incompatiable with inflationary universe models, indirectly providing observational support for these new theories.

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Inflation, Microwave Background Anisotropy, and Open Universe Models

Symposium - International Astronomical Union ◽

10.1017/s0074180900110198 ◽

1996 ◽

Vol 168 ◽

pp. 321-327

Author(s):

J.A. Frieman

Keyword(s):

Early Universe ◽

Large Scale ◽

Large Scale Structure ◽

Density Fluctuations ◽

Inhomogeneous Distribution ◽

Microwave Background ◽

Inflationary Scenario ◽

Open Universe ◽

The Universe ◽

Universe Models

The inflationary scenario for the very early universe has proven very attractive, because it can simultaneously solve a number of cosmological puzzles, such as the homogeneity of the Universe on scales exceeding the particle horizon at early times, the flatness or entropy problem, and the origin of density fluctuations for large-scale structure [1]. In this scenario, the observed Universe (roughly, the present Hubble volume) represents part of a homogeneous inflated region embedded in an inhomogeneous space-time. On scales beyond the size of this homogeneous patch, the initially inhomogeneous distribution of energy-momentum that existed prior to inflation is preserved, the scale of the inhomogeneities merely being stretched by the expansion.

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Renormalization Group Flows and Early Universe Models

Noncommutative Cosmology ◽

10.1142/9789813202856_0002 ◽

2017 ◽

pp. 61-88

Keyword(s):

Renormalization Group ◽

Early Universe ◽

Renormalization Group Flows ◽

Universe Models

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Acoustics of the early universe: flat versus open universe models

Classical and Quantum Gravity ◽

10.1088/0264-9381/18/3/313 ◽

2001 ◽

Vol 18 (3) ◽

pp. 543-554 ◽

Cited By ~ 2

Author(s):

Zdzislaw A Golda ◽

Andrzej Woszczyna

Keyword(s):

Early Universe ◽

Open Universe ◽

Universe Models

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Some topics on scale-invariant perturbations from noninflationary universe

International Journal of Modern Physics D ◽

10.1142/s0218271817400053 ◽

2017 ◽

Vol 26 (01) ◽

pp. 1740005 ◽

Cited By ~ 1

Author(s):

Mingzhe Li

Keyword(s):

Early Universe ◽

Main Property ◽

Scalar Fields ◽

Scalar Perturbation ◽

Scale Invariant ◽

Production Scale ◽

Tensor Perturbation ◽

Invariant Tensor ◽

Cyclic Universe ◽

Universe Models

In this paper, we review some topics on generations of scale-invariant primordial scalar and tensor perturbations in the early universe models different from inflation. The content includes generation of scale-invariant and Gaussian scalar perturbation in the ekpyrotic/cyclic universe, and production scale-invariant tensor perturbation in contracting universe. The main property of the models reviewed in this paper is the nonminimal couplings, include nonminimal couplings between the scalar fields and those to the gravity. By introducing these couplings, it is not difficult to achieve scale-invariances for the perturbations in the early universe models alternative to inflation.

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