scholarly journals The growth of the density fluctuations in the scale-invariant vacuum theory

2019 ◽  
Vol 25 ◽  
pp. 100315 ◽  
Author(s):  
Andre Maeder ◽  
Vesselin G. Gueorguiev
Keyword(s):  
Density Fluctuations ◽  
Scale Invariant ◽  
Vacuum Theory

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.

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 Dynamical attractors in contracting spacetimes dominated by kinetically coupled scalar fields

2021 ◽  
Vol 2021 (12) ◽  
pp. 030
Author(s):  
Anna Ijjas ◽  
Frans Pretorius ◽  
Paul J. Steinhardt ◽  
David Garfinkle
Keyword(s):  
Scalar Field ◽  
Initial Conditions ◽  
Scalar Fields ◽  
Density Fluctuations ◽  
Microwave Background ◽  
Scale Invariant ◽  
Linear Evolution ◽  
Kinetic Coupling ◽  
Wide Range ◽  
Non Linear

Abstract We present non-perturbative numerical relativity simulations of slowly contracting spacetimes in which the scalar field driving slow contraction is coupled to a second scalar field through an exponential non-linear σ model-type kinetic interaction. These models are important because they can generate a nearly scale-invariant spectrum of super-Hubble density fluctuations fully consistent with cosmic microwave background observations. We show that the non-linear evolution rapidly approaches a homogeneous, isotropic and flat Friedmann-Robertson-Walker (FRW) geometry for a wide range of inhomogeneous and anisotropic initial conditions. Ultimately, we find, the kinetic coupling causes the evolution to deflect away from flat FRW and towards a novel Kasner-like stationary point, but in general this occurs on time scales that are too long to be observationally relevant.

scholarly journals The Scale-Invariant Vacuum (SIV) Theory: A Possible Origin of Dark Matter and Dark Energy

Universe ◽  
2020 ◽  
Vol 6 (3) ◽  
pp. 46 ◽  
Author(s):  
Andre Maeder ◽  
Vesselin G. Gueorguiev
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Empty Space ◽  
Field Approximation ◽  
Weak Field ◽  
Density Fluctuations ◽  
Scale Invariant ◽  
Newtonian Approximation ◽  
Age Of The Universe ◽  
The Universe

The Scale Invariant Vacuum (SIV) theory rests on the basic hypothesis that the macroscopic empty space is scale invariant. This hypothesis is applied in the context of the Integrable Weyl Geometry, where it leads to considerable simplifications in the scale covariant cosmological equations. After an initial explosion and a phase of braking, the cosmological models show a continuous acceleration of the expansion. Several observational tests of the SIV cosmology are performed: on the relation between H 0 and the age of the Universe, on the m − z diagram for SNIa data and its extension to z = 7 with quasars and GRBs, and on the H ( z ) vs. z relation. All comparisons show a very good agreement between SIV predictions and observations. Predictions for the future observations of the redshift drifts are also given. In the weak field approximation, the equation of motion contains, in addition to the classical Newtonian term, an acceleration term (usually very small) depending on the velocity. The two-body problem is studied, showing a slow expansion of the classical conics. The new equation has been applied to clusters of galaxies, to rotating galaxies (some proximities with Modifies Newtonian Dynamics, MOND, are noticed), to the velocity dispersion vs. the age of the stars in the Milky Way, and to the growth of the density fluctuations in the Universe. We point out the similarity of the mechanical effects of the SIV hypothesis in cosmology and in the Newtonian approximation. In both cases, it results in an additional acceleration in the direction of motions. In cosmology, these effects are currently interpreted in terms of the dark energy hypothesis, while in the Newtonian approximation they are accounted for in terms of the dark matter (DM) hypothesis. These hypotheses appear no longer necessary in the SIV context.

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.

scholarly journals Scale invariant density perturbations from cyclic cosmology

2016 ◽  
Vol 31 (13) ◽  
pp. 1650076 ◽  
Author(s):  
Paul Howard Frampton
Keyword(s):  
Large Scale ◽  
Quantum Fluctuations ◽  
Large Scale Structure ◽  
Density Fluctuations ◽  
Scale Structure ◽  
Invariant Density ◽  
Scale Invariant ◽  
Density Perturbations

It is shown how quantum fluctuations of the radiation during the contraction era of a comes back empty (CBE) cyclic cosmology can provide density fluctuations which re-enter the horizon during the subsequent expansion era and at lowest order are scale invariant, in a Harrison–Zel’dovich–Peebles sense. It is necessary to be consistent with observations of large scale structure.

ON THE ORIGIN OF DENSITY FLUCTUATIONS IN THE UNIVERSE

1993 ◽  
Vol 08 (14) ◽  
pp. 1285-1290 ◽  
Author(s):  
M. D. POLLOCK
Keyword(s):  
Background Radiation ◽  
Density Fluctuations ◽  
Microwave Background ◽  
Superstring Theory ◽  
Scale Invariant ◽  
Order Unity ◽  
Microwave Background Radiation ◽  
Axion Decay Constant ◽  
Axion Decay ◽  
The Universe

It has been shown by Harrison that quantum fluctuations of the metric at the Planck era lead to a scale-invariant spectrum of density fluctuations ξ ≡ δρ/ρ at all subsequent times of the expansion of a Friedmann universe, irrespective of whether there is inflation. For the vacuum Einstein theory, ξ is of order unity, and thus is too large. But for the dimensionally reduced, heterotic superstring, ξ ≈ πfα/M P ≈ 6 × 10−4, where M P is the Planck mass and fa ≈ 2 × 10−4M P is the axion decay constant. This result is in approximate agreement with the observations of the temperature fluctuations in the cosmic microwave background radiation by COBE, δT/T ≈ 6 × 10−6, and thus constitutes evidence in favor of the superstring theory.

scholarly journals EFFECTS OF THE GENERALIZED UNCERTAINTY PRINCIPLE ON THE INFLATION PARAMETERS

2010 ◽  
Vol 19 (05) ◽  
pp. 513-521 ◽  
Author(s):  
KOUROSH NOZARI ◽  
SIAMAK AKHSHABI
Keyword(s):  
Quantum Gravity ◽  
Spectral Index ◽  
Early Universe ◽  
Uncertainty Principle ◽  
Generalized Uncertainty Principle ◽  
Density Fluctuations ◽  
Scale Invariant ◽  
Gravitational Effects ◽  
Gravity Effects

We investigate the effects of the generalized uncertainty principle on the inflationary dynamics of the early universe from both the standard and the braneworld viewpoint. We choose the Randall–Sundrum II model as our underlying braneworld scenario. We find that the quantum-gravitational effects lead to a spectral index which is not scale-invariant. Also, the amplitude of density fluctuations is reduced by increasing the strength of quantum-gravitational corrections. However, the tensor-to-scalar ratio increases by incorporation of these quantum gravity effects. We outline possible manifestations of these quantum gravity effects in the recent and future observations.

scholarly journals H i column density statistics of the cold neutral medium from absorption studies

2019 ◽  
Author(s):  
Pavan Kumar Vishwakarma ◽  
Prasun Dutta
Keyword(s):  
Thermal Properties ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Density Fluctuations ◽  
Neutral Medium ◽  
Spin Temperature ◽  
Scale Invariant ◽  
Absorption Studies ◽  
Scale Structures ◽  
Invariant Properties

Abstract Physical properties of the tiny scale structures in the cold neutral medium (CNM) of galaxies is a long-standing puzzle. Only a few lines of sights in our Galaxy have been studies with mixed results on the scale-invariant properties of such structures. Moreover, since these studies measure the variation of neutral hydrogen optical depth, they do not directly constrain the density structures. In this letter, we investigate the possibility of measuring the properties of density and spin temperature structures of the H i from absorption studies of H i . Our calculations show that irrespective of the thermal properties of the clouds, the scale structure of the H i column density can be estimated, whereas, H i absorption studies alone cannot shed much light on either the amplitude of the density fluctuations and their temperature structures. Detailed methodology and calculations with some fiducial examples are presented.

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