scholarly journals Nearly scale-invariant spectrum of adiabatic fluctuations may be from a very slowly expanding phase of the Universe

2003 ◽  
Vol 68 (8) ◽  
Author(s):  
Yun-Song Piao ◽  
E. Zhou
Keyword(s):  
Scale Invariant ◽  
Adiabatic Fluctuations ◽  
The Universe

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.

A holographic big bang?

2015 ◽  
Vol 24 (12) ◽  
pp. 1544029
Author(s):  
N. Afshordi ◽  
R. B. Mann ◽  
R. Pourhasan
Keyword(s):  
Cosmological Model ◽  
Big Bang ◽  
Initial Singularity ◽  
Scale Invariant ◽  
The Big Bang ◽  
The Universe ◽  
Important Test

We present a cosmological model in which the Universe emerges out of the collapse of a five-dimensional (5D) star as a spherical three-brane. The initial singularity of the big bang becomes hidden behind a causal horizon. Near scale-invariant primordial curvature perturbations can be induced on the brane via a thermal atmosphere that is in equilibrium with the brane, circumventing the need for a separate inflationary process and providing an important test of the model.

scholarly journals SUPERLUMINARY UNIVERSE: A POSSIBLE SOLUTION TO THE INITIAL VALUE PROBLEM IN COSMOLOGY

1993 ◽  
Vol 02 (03) ◽  
pp. 351-365 ◽  
Author(s):  
J.W. MOFFAT
Keyword(s):  
Lorentz Invariance ◽  
Critical Time ◽  
Spontaneous Breaking ◽  
Scale Invariant ◽  
First Order Phase Transition ◽  
Measured Speed ◽  
First Order Phase ◽  
The Universe ◽  
Local Lorentz Invariance ◽  
Flatness Problem

The spontaneous breaking of local Lorentz invariance in the early Universe, associated with a first order phase transition at a critical time tc, generates a large increase in the speed of light and a superluminary communication of information occurs, allowing all regions in the Universe to be causally connected. This solves the horizon problem, leads to a mechanism of monopole suppression in cosmology and can resolve the flatness problem. After the critical time tc, local Lorentz (and diffeomorphism) invariance is restored and light travels at its presently measured speed. The kinematical and dynamical aspects of the generation of quantum fluctuations in the superluminary Universe are investigated. A scale invariant prediction for the fluctuation density amplitude is obtained.

ON THE SPECTRUM OF PRIMORDIAL DENSITY FLUCTUATIONS

2006 ◽  
Vol 15 (09) ◽  
pp. 1487-1499 ◽  
Author(s):  
M. D. POLLOCK
Keyword(s):  
Galaxy Formation ◽  
Gravitational Constant ◽  
Higher Dimensions ◽  
Density Fluctuations ◽  
Density Contrast ◽  
Superstring Theory ◽  
Dimensional Theory ◽  
Scale Invariant ◽  
Higher Derivative ◽  
The Universe

The problem of the origin and spectrum of cosmic density fluctuations is discussed, especially with reference to the heterotic superstring theory of Gross et al. It is shown that primordial variation of the gravitational constant, due to its renormalization by higher-derivative terms [Formula: see text] dependent on the moduli, or the Harrison mechanism applied at the Hagedorn temperature T H = 1.14 × 1017 GeV (where we have argued that the four-dimensional theory decompactifies to higher dimensions), both naturally give rise to the scale-invariant spectrum of Zeldovich with a density contrast δ ~ 10-4-10-3, as required by the indeterminacy principle and for galaxy formation in the Universe.

scholarly journals UNIMODULAR CONSTRAINT ON GLOBAL SCALE INVARIANCE

2013 ◽  
Vol 28 (30) ◽  
pp. 1350130 ◽  
Author(s):  
NAVEEN K. SINGH
Keyword(s):  
Scale Invariance ◽  
Cosmological Solution ◽  
Field Approximation ◽  
Global Scale ◽  
De Sitter ◽  
Schwarzschild Solution ◽  
Scale Invariant ◽  
Conformal Theory ◽  
Rotational Curve ◽  
The Universe

We study a model with global scale invariance within the framework of unimodular gravity. The global scale invariant gravitational action which follows the unimodular general coordinate transformations is considered without invoking any scalar field. This is generalization of conformal theory described [P. D. Mannheim and D. Kazanas, Astrophys. J. 342, 635 (1989)]. The possible solutions for the gravitational potential under static linear field approximation are discussed. The new modified solution has additional corrections to the Schwarzschild solution which describe the galactic rotational curve. A comparative study of unimodular theory with conformal theory is also presented. Furthermore, the cosmological solution is studied and it is shown that the unimodular constraint preserve the de Sitter solution explaining the dark energy of the universe.

ON THE HEISENBERG INDETERMINACY PRINCIPLE AND THE FORMATION OF STRUCTURE IN THE UNIVERSE

1995 ◽  
Vol 10 (07) ◽  
pp. 539-547 ◽  
Author(s):  
M. D. POLLOCK
Keyword(s):  
Background Radiation ◽  
Density Fluctuations ◽  
Internal Space ◽  
Superstring Theory ◽  
Scale Invariant ◽  
Classical Action ◽  
Four Dimensions ◽  
Dimensionless Constant ◽  
Microwave Background Radiation ◽  
The Universe

The Heisenberg indeterminacy principle ΔpaΔqa ~ ħ, relating canonically conjugate variables pa and qa, is quantified for the classical action obtained by the reduction of the ten-dimensional heterotic superstring theory to four dimensions, in the mini-superspace (Friedmann space-time) [Formula: see text]. There are two coordinates, α and [Formula: see text], representing position and velocity, respectively, the canonical momenta being [Formula: see text] and [Formula: see text]. In both cases, the result can be expressed as an indeterminacy in the time, (Δt/t)2. The fluctuations connecting position and velocity decrease with time and are always undetectably small, Δt/t ≲ 10−44. But the fluctuations involving velocity and acceleration increase with time, and are evaluated at the time te of equipartition of radiation and matter in the universe. Translated first into a metric fluctuation [Formula: see text], this is equivalent to a Gaussian, scale-invariant spectrum of density fluctuations of magnitude [Formula: see text], where the dimensionless constant B depends only on the compactification scheme. For a Calabi–Yau internal space, the estimate B ≈ 3 implies that ζ ≈ 2 × 10−4, which is sufficient for the creation of galaxies and in approximate agreement with observations of the anisotropy of the cosmic microwave background radiation by COBE and at Tenerife.

scholarly journals Gravity as the breakdown of conformal invariance

2015 ◽  
Vol 24 (12) ◽  
pp. 1543002 ◽  
Author(s):  
Giovanni Amelino-Camelia ◽  
Michele Arzano ◽  
Giulia Gubitosi ◽  
João Magueijo
Keyword(s):  
Gravity Waves ◽  
Conformal Invariance ◽  
Scale Invariance ◽  
Big Bang ◽  
Two Dimensional ◽  
Top Down ◽  
Scale Invariant ◽  
Primordial Power Spectrum ◽  
The Big Bang ◽  
The Universe

In this paper, we propose that at the beginning of the universe gravity existed in a limbo either because it was switched off or because it was only conformally coupled to all particles. This picture can be reverse-engineered from the requirement that the cosmological perturbations be (nearly) scale-invariant without the need for inflation. It also finds support in recent results in quantum gravity suggesting that spacetime becomes two-dimensional at super-Planckian energies. We advocate a novel top-down approach to cosmology based on the idea that gravity and the Big Bang Universe are relics from the mechanism responsible for breaking the fundamental conformal invariance. Such a mechanism should leave clear signatures in departures from scale-invariance in the primordial power spectrum and the level of gravity waves generated.

scholarly journals Bose–Einstein condensation as an alternative to inflation

2015 ◽  
Vol 24 (12) ◽  
pp. 1544001 ◽  
Author(s):  
Saurya Das
Keyword(s):  
Ground State ◽  
Large Scale ◽  
Small Mass ◽  
Einstein Condensate ◽  
Einstein Condensation ◽  
Scale Invariant ◽  
Bose Einstein Condensate ◽  
Density Perturbations ◽  
Bose Einstein ◽  
The Universe

It was recently shown that gravitons with a very small mass should have formed a Bose–Einstein condensate (BEC) in the very early universe, whose density and quantum potential can account for the dark matter (DM) and dark energy (DE) in the universe respectively. Here, we show that the condensation can also naturally explain the observed large scale homogeneity and isotropy of the universe. Furthermore, gravitons continue to fall into their ground state within the condensate at every epoch, accounting for the observed flatness of space at cosmological distance scales. Finally, we argue that the density perturbations due to quantum fluctuations within the condensate give rise to a scale invariant spectrum. This therefore provides a viable alternative to inflation, which is not associated with the well-known problems associated with the latter.

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