scholarly journals Remarks on cosmology

1959 ◽  
Vol 9 ◽  
pp. 533-535
Author(s):  
G. C. Mcvittie
Keyword(s):  
A Priori ◽  
Initial Instant ◽  
De Sitter ◽  
Relativistic Model ◽  
Space Curvature ◽  
Composite Models ◽  
History Of ◽  
Sitter Model ◽  
The Universe ◽  
De Sitter Model

First, I should like to say something about the use of highly specialized models in cosmology. The Einstein—de Sitter model is a relativistic model in which the cosmical constant and the space-curvature constant are both equated to zero. Likewise, the pressure is assumed to be zero throughout the history of the universe, except perhaps at the initial instant. It is well-known that the first two constants can be determined from observation, if not at present, at any rate as the data are refined in the future. Hence, I think it is a weakness to prejudge the issue and assign a priori values. Nor is it self-evident to me that the pressure must always have been zero even if it is zero now. Composite models, with nonzero pressure at first, followed by a zero-pressure condition, need to be examined.

Nonminimal derivative coupling: Some cosmological behaviors of John and George models

2014 ◽  
Vol 23 (08) ◽  
pp. 1450067
Author(s):  
A. Kanfon ◽  
G. Edah ◽  
E. Baloïtcha
Keyword(s):  
Exponential Function ◽  
Coupling Parameter ◽  
Big Bang ◽  
De Sitter ◽  
Stiff Matter ◽  
Derivative Coupling ◽  
Sitter Model ◽  
The Big Bang ◽  
The Universe ◽  
De Sitter Model

We examine some nonminimal derivative coupling models with a term of potential in front of the Ricci scalar–tensor. We limited ourselves to three models of this family: — the potential proportional to the square of the field — the potential proportional to the inverse of the field — the potential proportional to the exponential function of the field. The first one leads to an universe which closes a few moment after its creation. The two other models show an accelerated expanding universe after inflation. The model with a potential proportional to the exponential function of the field, pointed out, just after the big bang primordial, the predominance of dark energy guiding inflation. At the end of inflation, in its expansion, the universe tends to de Sitter model dominated by the stiff matter. These results are those obtained by using the potential which is a linear function of the field. What is interesting about this model is that these results are not very sensitive to variations of the coupling parameter and the initial velocity of the field.

Can the Einstein-de Sitter model adequately describe the Universe at any epoch?

1978 ◽  
Vol 58 (1) ◽  
pp. 181-188
Author(s):  
A. Gordon Emslie ◽  
Robin M. Green
Keyword(s):  
De Sitter ◽  
Sitter Model ◽  
The Universe ◽  
De Sitter Model

scholarly journals Gravitation with Cosmological Term, Expansion of the Universe as Uniform Acceleration in Clifford Coordinates

2021 ◽  
Author(s):  
Alexander Kritov
Keyword(s):  
Clifford Algebra ◽  
Cosmological Term ◽  
Two Dimensional ◽  
De Sitter ◽  
Time Coordinate ◽  
Dimensional Spacetime ◽  
Expansion Of The Universe ◽  
Sitter Model ◽  
The Universe ◽  
De Sitter Model

The paper briefly reviews the Clifford algebras of space Cl(3,0) and anti-space Cl(0,3) with a particular focus on the paravector representation, emphasizing the fact that both algebras have an isomorphic center represented just by two coordinates. Since the paravector representation allows assigning the scalar element of grade 0 to the time coordinate, we consider the relativity in such two-dimensional spacetime for a uniformly accelerated frame with the constant acceleration 3Hc. Using the Rindler coordinate transformations in two-dimensional spacetime and then applying it to Minkowski coordinates, we obtain the FLRW metric, which in the case of the Clifford algebra of space Cl(3,0) corresponds to the anti-de Sitter (AdS) flat (k=0) case, the negative cosmological term and an oscillating model of the universe. The approach with anti-Euclidean Clifford algebra Cl(0,3) leads to the de Sitter model with the positive cosmological term and the exact form of the scale factor used in modern cosmology.

scholarly journals On space and time in quantum cosmology

2002 ◽  
Vol 2 (4) ◽  
pp. 173-182 ◽  
Author(s):  
Ljubisa Nesic ◽  
Stojan Obradovic
Keyword(s):  
Quantum Cosmology ◽  
De Sitter ◽  
Real Numbers ◽  
Standard Quantum ◽  
Space And Time ◽  
Sitter Model ◽  
Basic Ideas ◽  
The Universe ◽  
Early Phases ◽  
De Sitter Model

The paper considers the properties of space and time in quantum cosmology. It presented the basic ideas of the substantial and relational conceptions of space and time, as well the basic ideas of the continuity and discreteness of space and time. The basics of standard quantum cosmology, i.e. quantum cosmology formulated over the field of real numbers R, have also been presented. Quantum cosmology is the application of the quantum theory to the universe as a whole in the early phases of its evolution, when the universe was very small so that all the four interactions were practically unified. In order to obtain the maximum possible information from quantum cosmology it is necessary that it be "complete". The concept "complete" refers here to the formulation of the theory over the field of real numbers and the field of p-adic numbers Qp. Since p-adic numbers are generally not well-known, the idea of their introduction has carefully been considered. Within the p-adic quantum cosmology representing quantum cosmology over the field of p-adic numbers Qp, the main results concerning the de Sitter model have been presented. The consequence of this (complete) formulation of the de Sitter model is the radius discreteness of the universe.

scholarly journals Historical and philosophical reflections on the Einstein-de Sitter model

2021 ◽  
Vol 46 (1) ◽  
Author(s):  
Cormac O’Raifeartaigh ◽  
Michael O’Keeffe ◽  
Simon Mitton
Keyword(s):  
De Sitter ◽  
Sitter Model ◽  
De Sitter Model

Is the Einstein de Sitter model actually ruled out?

2003 ◽  
Vol 124 ◽  
pp. 87-90
Author(s):  
A. Blanchard
Keyword(s):  
De Sitter ◽  
Sitter Model ◽  
De Sitter Model

scholarly journals Geometric Models of the Quantum Relativistic Rotating Oscillator

1997 ◽  
Vol 12 (10) ◽  
pp. 685-690 ◽  
Author(s):  
Ion I. Cotăescu
Keyword(s):  
Fine Structure ◽  
Harmonic Oscillator ◽  
Nonrelativistic Limit ◽  
Energy Spectra ◽  
De Sitter ◽  
Continuous Part ◽  
Geometric Models ◽  
Isotropic Harmonic Oscillator ◽  
Sitter Model ◽  
De Sitter Model

A family of geometric models of quantum relativistic rotating oscillator is defined by using a set of one-parameter deformations of the static (3+1) de Sitter or anti-de Sitter metrics. It is shown that all these models lead to the usual isotropic harmonic oscillator in the nonrelativistic limit, even though their relativistic behavior is different. As in the case of the (1+1) models,1 these will have even countable energy spectra or mixed ones, with a finite discrete sequence and a continuous part. In addition, all these spectra, except that of the pure anti-de Sitter model, will have a fine-structure, given by a rotator-like term.

scholarly journals 2D relativistic oscillators with a uniform magnetic field in anti-de Sitter space

2021 ◽  
pp. 2150113
Author(s):  
Lakhdar Sek ◽  
Mokhtar Falek ◽  
Mustafa Moumni
Keyword(s):  
Magnetic Field ◽  
Uniform Magnetic Field ◽  
Principal Quantum Number ◽  
Wave Functions ◽  
De Sitter ◽  
Energy Eigenvalues ◽  
Space Deformation ◽  
Klein Gordon ◽  
Sitter Model ◽  
De Sitter Model

We study analytically the two-dimensional deformed bosonic oscillator equation for charged particles (both spin 0 and spin 1 particles) subject to the effect of an uniform magnetic field. We consider the presence of a minimal uncertainty in momentum caused by the anti-de Sitter model and we use the Nikiforov–Uvarov (NU) method to solve the system. The exact energy eigenvalues and the corresponding wave functions are analytically obtained for both Klein–Gordon and scalar Duffin–Kemmer–Petiau (DKP) cases and we find that the deformed spectrum remains discrete even for large values of the principal quantum number. For spin 1 DKP case, we deduce the behavior of the DKP equation and write the nonrelativistic energies and we show that the space deformation adds a new spin-orbit interaction proportional to its parameter. Finally, we study the thermodynamic properties of the system and here we find that the effects of the deformation on the statistical properties are important only in the high-temperature regime.

scholarly journals Note On A Super-Horizon-Scale Inhomogeneous Cosmological Model

1996 ◽  
Vol 173 ◽  
pp. 25-26
Author(s):  
K. Tomita
Keyword(s):  
Large Scale ◽  
Background Radiation ◽  
Theoretical Explanation ◽  
Cosmological Models ◽  
Low Density ◽  
De Sitter ◽  
Number Count ◽  
Microwave Background Radiation ◽  
Sitter Model ◽  
De Sitter Model

Many observations of large-scale and cosmological structures in the universe have been collected, but so far there is no consistent theoretical explanation. In the region within 100 Mpc from us, the observed two-point correlations of galaxies and clusters of galaxies can be described well by low-density homogeneous cosmological models (Bahcall & Cen 1993; Suto 1993). On the other hand, the observed anisotropies of the cosmic microwave background radiation have been explained well by comparatively high-density cosmological models such as the Einstein-de Sitter model (Bunn & Sugiyama 1994). In the intermediate scale, the angular sizes of the cores of quasars have been measured and their redshift dependence has been shown to be more consistent with the Einstein-de Sitter model than with the low-density models (Kellermann 1993). The number count-magnitude relation for remote galaxies supports low-density models with a nonzero cosmological constant (for example, Fukugita et al. 1990), but these models may be inconsistent with the observed distribution of Lyα clouds (Fukugita & Lahav 1991).

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