scholarly journals Comparative Analysis of Standard ΛCDM and ΛCS Models

2021 ◽  
Vol 57 (11) ◽  
pp. 1169
Author(s):  
V.E. Kuzmichev ◽  
V.V. Kuzmichev
Keyword(s):  
Cosmological Constant ◽  
Semiclassical Approximation ◽  
Cosmic Strings ◽  
Cosmological Parameters ◽  
Einstein Equations ◽  
Scale Transformation ◽  
De Sitter ◽  
Field Equations ◽  
Low Velocity ◽  
Sitter Model

We draw a comparison of time-dependent cosmological parameters calculated in the standard ΛCDM model with those of the model of a homogeneous and isotropic Universe with non-zero cosmological constant filled with a perfect gas of low-velocity cosmic strings (ΛCS model). It is shown that pressure-free matter can obtain the properties of a gas of low-velocity cosmic strings in the epoch, when the global geometry and the total amount of matter in the Universe as a whole obey an additional constraint. This constraint follows from the quantum geometrodynamical approach in the semiclassical approximation. In terms of general relativity, its effective contribution to the field equations can be linked to the time evolution of the equation of state of matter caused by the processes of redistribution of the energy between matter components. In the present article, the exact solutions of the Einstein equations for the ΛCS model are found. It is demonstrated that this model is equivalent to the open de Sitter model. After the scale transformation of the time variable of the ΛCS model, the standard ΛCDM and ΛCS models provide the equivalent descriptions of cosmological parameters as functions of time at equal values of the cosmological constant. The exception is the behavior of the deceleration parameter in the early Universe.

scholarly journals Cosmological model favored by the holographic principle

2016 ◽  
Vol 41 ◽  
pp. 1660127
Author(s):  
Irina Dymnikova ◽  
Anna Dobosz ◽  
Bożena Sołtysek
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Space Time ◽  
Holographic Principle ◽  
Einstein Equations ◽  
Energy Tensor ◽  
De Sitter ◽  
Quantum Evaporation ◽  
Stress Energy ◽  
De Sitter Vacua

We present a regular spherically symmetric cosmological model of the Lemaitre class distinguished by the holographic principle as the thermodynamically stable end-point of quantum evaporation of the cosmological horizon. A source term in the Einstein equations connects smoothly two de Sitter vacua with different values of cosmological constant and corresponds to anisotropic vacuum dark fluid defined by symmetry of its stress-energy tensor which is invariant under the radial boosts. Global structure of space-time is the same as for the de Sitter space-time. Cosmological evolution goes from a big initial value of the cosmological constant towards its presently observed value.

scholarly journals THE NATURE OF Λ AND THE MASS OF THE GRAVITON: A CRITICAL VIEW

2011 ◽  
Vol 03 ◽  
pp. 3-26 ◽  
Author(s):  
J.-P. GAZEAU ◽  
M. NOVELLO
Keyword(s):  
Cosmological Constant ◽  
Einstein Equation ◽  
Universal Constant ◽  
Einstein Equations ◽  
Theoretical Interpretation ◽  
De Sitter ◽  
Current Estimate ◽  
Left Hand ◽  
Fundamental State ◽  
The Right

The observational evidence of a cosmological constant Λ raises natural questions. Is Λ a universal constant fixing the geometry of an empty universe, as fundamental as the Planck constant or the speed of light in the vacuum? Its natural place is then on the left-hand side of the Einstein equation. Is it instead something emerging from a perturbation calculation performed on the metric gμν solution of the Einstein equation and to which it might be given a material status of (dark or bright) "energy"? It should then be part of the content of the right-hand side of the Einstein equations. The purpose of this paper is to analyze some of the arguments in favor of each one of these interpretations of the cosmological constant. Recent estimates based on observational data give a bound on the graviton mass to be about 100 Mpc-1. If this value and the current estimate on the cosmological constant Λ are put into perspective, one faces the interesting coincidence that between the Compton wavelength of the graviton and the cosmological constant there exists the relation [Formula: see text]. Since a physical quantity like mass originates in a minkowskian conservation law, we proceed with a group theoretical interpretation of this relation in terms of the two possible Λ-deformations of the Poincaré group, namely the de Sitter and anti de Sitter groups. We use a very suitable formula, the so-called Garidi mass, and the typically dS/AdS dimensionless parameter ℏH/mc2 in order to make clear the asymptotic relations between minkowskian masses m and their possible dS/AdS counterparts. We conclude that if the fundamental state of the geometry of space-time is minkowskian, then the square of the mass of the graviton is proportional to Λ; otherwise, if the fundamental state is de Sitter, then the graviton is massless in the deSitterian sense.

scholarly journals Fingerprints of the Cosmological Constant: Folds in the Profiles of the Axionic Dark Matter Distribution in a Dyon Exterior

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 455 ◽  
Author(s):  
Alexander Balakin ◽  
Dmitry Groshev
Keyword(s):  
Dark Matter ◽  
Cosmological Constant ◽  
Electric Fields ◽  
Double Electric Layer ◽  
De Sitter ◽  
Electric Structure ◽  
Near Zone ◽  
Sitter Model ◽  
Dark Matter Distribution ◽  
The Right

We consider the magnetic monopole in the axionic dark matter environment (axionic dyon) in the framework of the Reissner-Nordström-de Sitter model. Our aim is to study the distribution of the pseudoscalar (axion) and electric fields near the so-called folds, which are characterized by the profiles with the central minimum, the barrier on the left, and the maximum on the right of this minimum. The electric field in the fold-like zones is shown to change the sign twice, i.e., the electric structure of the near zone of the axionic dyon contains the domain similar to a double electric layer. We have shown that the described fold-like structures in the profile of the gravitational potential, and in the profiles of the electric and axion fields can exist, when the value of the dyon mass belongs to the interval enclosed between two critical masses, which depend on the cosmological constant.

scholarly journals Null hypersurfaces in de Sitter and anti-de Sitter cosmologies

2018 ◽  
Vol 27 (04) ◽  
pp. 1850045
Author(s):  
P. A. Hogan
Keyword(s):  
Cosmological Constant ◽  
Gravitational Waves ◽  
Constant Curvature ◽  
Focus Attention ◽  
De Sitter ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Null Hypersurfaces ◽  
Einstein's Field Equations ◽  
Line Elements

The study of gravitational waves in the presence of a cosmological constant has led to interesting forms of the de Sitter and anti-de Sitter line elements based on families of null hypersurfaces. The forms are interesting because they focus attention on the geometry of null hypersurfaces in spacetimes of constant curvature. Two examples are worked out in some detail. The first originated in the study of collisions of impulsive gravitational waves in which the post-collision spacetime is a solution of Einstein’s field equations with a cosmological constant, and the second originated in the generalization of plane fronted gravitational waves with parallel rays to include a cosmological constant.

scholarly journals Designer de Sitter spacetimes

2008 ◽  
Vol 86 (4) ◽  
pp. 591-595
Author(s):  
K Schleich ◽  
D M Witt
Keyword(s):  
Cosmological Constant ◽  
Infinite Family ◽  
Einstein Equations ◽  
Global Dynamics ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Isotropic Solution ◽  
Accelerating Expansion ◽  
Sitter Spacetime ◽  
Expansion Of The Universe

Recent observations in cosmology indicate an accelerating expansion of the Universe postulated to arise from some form of dark energy, the paradigm being positive cosmological constant. De Sitter spacetime is the well-known isotropic solution to the Einstein equations with cosmological constant. However, as discussed here, it is not the most general, locally isotropic solution. One can construct an infinite family of such solutions, designer de Sitter spacetimes, which are everywhere locally isometric to a region of de Sitter spacetime. However, the global dynamics of these designer cosmologies is very different than that of de Sitter spacetime itself. The construction and dynamics of these designer de Sitter spacetimes is detailed along with some comments about their implications for the structure of our Universe.PACS Nos.: 04.20.–q, 04.20.Ex, 04.20.Gz, 98.80.–k

scholarly journals THE NATURE OF Λ AND THE MASS OF THE GRAVITON: A CRITICAL VIEW

2011 ◽  
Vol 26 (22) ◽  
pp. 3697-3720 ◽  
Author(s):  
J.-P. GAZEAU ◽  
M. NOVELLO
Keyword(s):  
Cosmological Constant ◽  
Einstein Equation ◽  
Universal Constant ◽  
Einstein Equations ◽  
Theoretical Interpretation ◽  
De Sitter ◽  
Current Estimate ◽  
Left Hand ◽  
Fundamental State ◽  
The Right

The observational evidence of a cosmological constant Λ raises natural questions. Is Λ a universal constant fixing the geometry of an empty universe, as fundamental as the Planck constant or the speed of light in the vacuum? Its natural place is then on the left-hand side of the Einstein equation. Is it instead something emerging from a perturbation calculation performed on the metric gμν solution of the Einstein equation and to which it might be given a material status of (dark or bright) "energy"? It should then be part of the content of the right-hand side of the Einstein equations. The purpose of this paper is to analyze some of the arguments in favor of each one of these interpretations of the cosmological constant. Recent estimates based on observational data give a bound on the graviton mass to be about 100 Mpc-1. If this value and the current estimate on the cosmological constant Λ are put into perspective, one faces the interesting coincidence that between the Compton wavelength of the graviton and the cosmological constant there exists the relation [Formula: see text]. Since a physical quantity like mass originates in a minkowskian conservation law, we proceed with a group theoretical interpretation of this relation in terms of the two possible Λ-deformations of the Poincaré group, namely the de Sitter and anti de Sitter groups. We use a very suitable formula, the so-called Garidi mass, and the typically dS/AdS dimensionless parameter ħH/mc2 in order to make clear the asymptotic relations between minkowskian masses m and their possible dS/AdS counterparts. We conclude that if the fundamental state of the geometry of space-time is minkowskian, then the square of the mass of the graviton is proportional to Λ; otherwise, if the fundamental state is de Sitter, then the graviton is massless in the deSitterian sense.

scholarly journals “MODULI SPACE” OF ASYMPTOTICALLY ANTI-DE-SITTER SPACE-TIMES IN 2+1 DIMENSIONS

1995 ◽  
Vol 10 (29) ◽  
pp. 4139-4160 ◽  
Author(s):  
KIYOSHI EZAWA
Keyword(s):  
Black Holes ◽  
General Solution ◽  
Power Series ◽  
Cosmological Constant ◽  
Moduli Space ◽  
Three Dimensional ◽  
Einstein Equations ◽  
Quadratic Differentials ◽  
De Sitter ◽  
Inverse Radius

Setting an ansatz that the metric is expressible by a power series of the inverse radius and taking a particular gauge choice, we construct a “general solution” of (2+1)-dimensional Einstein equations with a negative cosmological constant in the case where the space-time is asymptotically anti-de-Sitter. Our general solution turns out to be parametrized by two centrally extended quadratic differentials on S1. In order to include three-dimensional black holes naturally in our general solution, it is necessary to exclude the region inside the horizon. We also discuss the relation of our general solution to the moduli space of flat [Formula: see text] connections.

scholarly journals Bardeen–de Sitter black holes

2017 ◽  
Vol 26 (07) ◽  
pp. 1750071 ◽  
Author(s):  
Sharmanthie Fernando
Keyword(s):  
Black Hole ◽  
Cosmological Constant ◽  
Cross Sections ◽  
Einstein Equations ◽  
Nonlinear Electrodynamics ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
De Sitter ◽  
Third Order ◽  
Regular Black Hole

In this paper, we present a regular black hole with a positive cosmological constant. The regular black hole considered is the well known Bardeen black hole and it is a solution to the Einstein equations coupled to nonlinear electrodynamics with a magnetic monopole. The paper discusses the properties of the Bardeen–de Sitter black hole. We have computed the gray body factors and partial absorption cross-sections for massless scalar field impinges on this black hole with the third-order WKB approximation. A detailed discussion on how the behavior of the gray body factors depend on the parameters of the theory such as the mass, charge and the cosmological constant is given. Possible extensions of the work is discussed at the end of the paper.

scholarly journals Space-Time Second-Quantization Effects and the Quantum Origin of Cosmological Constant in Covariant Quantum Gravity

Symmetry ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 287 ◽  
Author(s):  
Claudio Cremaschini ◽  
Massimo Tessarotto
Keyword(s):  
Gravitational Field ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Proper Time ◽  
Theoretical Background ◽  
Space Time ◽  
Einstein Equations ◽  
Field Equations ◽  
Metric Tensor ◽  
Covariant Quantum

Space-time quantum contributions to the classical Einstein equations of General Relativity are determined. The theoretical background is provided by the non-perturbative theory of manifestly-covariant quantum gravity and the trajectory-based representation of the related quantum wave equation in terms of the Generalized Lagrangian path formalism. To reach the target an extended functional setting is introduced, permitting the treatment of a non-stationary background metric tensor allowed to depend on both space-time coordinates and a suitably-defined invariant proper-time parameter. Based on the Hamiltonian representation of the corresponding quantum hydrodynamic equations occurring in such a context, the quantum-modified Einstein field equations are obtained. As an application, the quantum origin of the cosmological constant is investigated. This is shown to be ascribed to the non-linear Bohm quantum interaction of the gravitational field with itself in vacuum and to depend generally also on the realization of the quantum probability density for the quantum gravitational field tensor. The emerging physical picture predicts a generally non-stationary quantum cosmological constant which originates from fluctuations (i.e., gradients) of vacuum quantum gravitational energy density and is consistent with the existence of quantum massive gravitons.

THEOREM TO GENERATE NON-SPHERICAL RADIATING BLACK HOLE SOLUTIONS

2008 ◽  
Vol 23 (15) ◽  
pp. 1115-1127
Author(s):  
V. S. MOROZOVA ◽  
S. G. GHOSH
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmological Constant ◽  
Einstein Equations ◽  
Energy Conditions ◽  
Type I ◽  
De Sitter ◽  
Sitter Background ◽  
Two Parameter ◽  
Black Hole Solutions

We prove a theorem that characterizes a two-parameter family of solutions to Einstein equations with a negative cosmological constant, representing, in general, non-spherical radiating black holes in an anti-de Sitter background. It is shown that the best known non-spherical radiating black hole solutions are particular cases and static non-spherical black hole solutions, for Type I fluid, are also retrieved. A brief discussion on the energy conditions, singularities and horizons is provided.

Sign in / Sign up

Export Citation Format

Share Document