scholarly journals Generation of a scale-invariant spectrum of adiabatic fluctuations in cosmological models with a contracting phase

2002 ◽  
Vol 65 (10) ◽  
Author(s):  
Fabio Finelli ◽  
Robert Brandenberger
Keyword(s):  
Cosmological Models ◽  
Scale Invariant ◽  
Contracting Phase ◽  
Adiabatic Fluctuations

scholarly journals Structure Constraints from Large Angle CMB Anisotropies

1992 ◽  
Vol 9 ◽  
pp. 319-321
Author(s):  
J. Richard Bond
Keyword(s):  
Correlation Function ◽  
Structure Formation ◽  
Large Distance ◽  
Large Angle ◽  
Microwave Background ◽  
Scale Invariant ◽  
Intermediate Angle ◽  
History Of ◽  
Adiabatic Fluctuations ◽  
The Universe

Constraints on models of cosmic structure formation that can be drawn from current limits on large angle microwave background anisotropies are now competitive with those from recent small and intermediate angle experiments and are relatively insensitive to the reheating history of the Universe. Here I give limits on Gaussian scale invariant adiabatic fluctuations and describe the role that the large angle results play in constraining models with enhanced large distance galaxy clustering power inferred from correlation function measurements is described.

scholarly journals BOUNCING MODELS WITH A COSMOLOGICAL CONSTANT

2011 ◽  
Vol 03 ◽  
pp. 294-302
Author(s):  
NELSON PINTO-NETO ◽  
BEATRIZ B. SIFFERT ◽  
RODRIGO MAIER ◽  
STELLA PEREIRA
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Initial Conditions ◽  
State Parameter ◽  
Vacuum State ◽  
Cosmological Perturbations ◽  
Scale Invariant ◽  
Stiff Matter ◽  
Equation Of State Parameter ◽  
Contracting Phase

Most bouncing models contain a contracting phase from a very large and rarefied state, where dark energy might have had an important role. If this is that case, the presence of dark energy can modify the initial conditions and evolution of cosmological perturbations, changing the known results already obtained in the literature concerning their amplitude and spectrum. In this work, we assume the simplest and most appealing candidate for dark energy, the cosmological constant, and study its influence on the evolution of cosmological perturbations during the contracting phase of a bouncing model, containing also a perfect fluid with constant equation of state parameter w. We show that, due to the vacuum state choice we have to make when a cosmological constant is present, the spectrum of the perturbations are substantially altered. We conclude that, in this case, the presence of a stiff matter fluid in the contracting phase is needed in order to have a scale invariant spectrum of perturbations in the expanding phase.

scholarly journals Global properties of locally spatially homogeneous cosmological models with matter

1995 ◽  
Vol 118 (3) ◽  
pp. 511-526 ◽  
Author(s):  
Alan D. Rendall
Keyword(s):  
Cosmological Models ◽  
Einstein Equations ◽  
Homogeneous Solutions ◽  
Perfect Fluids ◽  
Global Properties ◽  
Homogeneous Cosmological Models ◽  
Scalar Invariant ◽  
Spatially Homogeneous ◽  
Contracting Phase

AbstractThe existence and nature of singularities in locally spatially homogeneous solutions of the Einstein equations coupled to various phenoraenological matter models is investigated. It is shown that, under certain reasonable assumptions on the matter, there are no singularities in an expanding phase of the evolution and that unless the spacetime is empty a contracting phase always ends in a singularity where at least one scalar invariant of the curvature diverges uniformly. The class of matter models treated includes perfect fluids, mixtures of non-interacting perfect fluids and collisionless matter.

scholarly journals SCALE INVARIANT COSMOLOGY

1999 ◽  
Vol 08 (03) ◽  
pp. 271-289 ◽  
Author(s):  
PIERRE MIDY ◽  
JEAN-PIERRE PETIT
Keyword(s):  
Cosmological Models ◽  
Scale Invariant ◽  
Horizon Problem ◽  
Physical Scale

An attempt is made here to extend to the microscopic domain the scale invariant character of gravitation — which amounts to consider expansion as applying to any physical scale. Surprisingly, this hypothesis does not prevent the redshift from being obtained. It leads to strong restrictions concerning the choice between the presently available cosmological models and to new considerations about the notion of time. Moreover, there is no horizon problem and resorting to inflation is not necessary.

scholarly journals Ekpyrotic Nongaussianity: A Review

2010 ◽  
Vol 2010 ◽  
pp. 1-19 ◽  
Author(s):  
Jean-Luc Lehners
Keyword(s):  
Big Bang ◽  
Density Fluctuations ◽  
Scale Invariant ◽  
Scalar Density ◽  
Contracting Phase ◽  
The Big Bang ◽  
Near Future ◽  
The Universe

Ekpyrotic models and their cyclic extensions solve the standard cosmological flatness, horizon, and homogeneity puzzles by postulating a slowly contracting phase of the universe prior to the big bang. This ekpyrotic phase also manages to produce a nearly scale-invariant spectrum of scalar density fluctuations but, crucially, with significant nongaussian corrections. In fact, some versions of ekpyrosis are on the borderline of being ruled out by observations, while, interestingly, the best-motivated models predict levels of nongaussianity that will be measurable by near-future experiments. Here, we review these predictions in detail, and comment on their implications.

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