scholarly journals COASTING COSMOLOGIES WITH TIME DEPENDENT COSMOLOGICAL CONSTANT

1999 ◽  
Vol 14 (10) ◽  
pp. 1523-1529 ◽  
Author(s):  
LUIS O. PIMENTEL ◽  
LUZ M. DIAZ-RIVERA
Keyword(s):  
Cosmological Constant ◽  
Perfect Fluid ◽  
Gravitational Constant ◽  
Linear Expansion ◽  
Cosmological Models ◽  
Time Dependent ◽  
Expansion Factor ◽  
Fluid Matter ◽  
Friedmann Robertson Walker

The effect of a time dependent cosmological constant is considered in a family of scalar-tensor theories. Friedmann–Robertson–Walker cosmological models for vacuum and perfect fluid matter are found. They have a linear expansion factor, the so-called coasting cosmology, the gravitational "constant" decreases inversely with time; that is these models satisfy the Dirac Hypotheses. The cosmological "constant" decreases inversely with the square of time, therefore we can have a very small value for it at present time.

scholarly journals Five-Dimensional Space-Times with a Variable Gravitational and Cosmological Constant

2014 ◽  
Vol 2014 ◽  
pp. 1-4 ◽  
Author(s):  
Sanjay Oli
Keyword(s):  
Cosmological Constant ◽  
Perfect Fluid ◽  
Gravitational Constant ◽  
Dimensional Space ◽  
Space Time ◽  
Time Dependent ◽  
Field Equations ◽  
Current Observation ◽  
Kinematical Parameters ◽  
Kaluza Klein

We have presented cosmological models in five-dimensional Kaluza-Klein space-time with a variable gravitational constant (G) and cosmological constant (Λ). We have investigated Einstein’s field equations for five-dimensional Kaluza-Klein space-time in the presence of perfect fluid with time dependent G and Λ. A variety of solutions have been found in which G increases and Λ decreases with time t, which matches with current observation. The properties of fluid and kinematical parameters have been discussed in detail.

scholarly journals AN EARLY UNIVERSE MODEL WITH STIFF MATTER AND A COSMOLOGICAL CONSTANT

2011 ◽  
Vol 03 ◽  
pp. 254-265 ◽  
Author(s):  
G. OLIVEIRA-NETO ◽  
G. A. MONERAT ◽  
E. V. CORRÊA SILVA ◽  
C. NEVES ◽  
L. G. FERREIRA FILHO
Keyword(s):  
Cosmological Constant ◽  
Perfect Fluid ◽  
Scale Factor ◽  
Initial Singularity ◽  
Discrete Energy ◽  
Classical Level ◽  
Stiff Matter ◽  
Expectation Value ◽  
Variational Formalism ◽  
Friedmann Robertson Walker

In the present work, we study the quantum cosmology description of a Friedmann-Robertson-Walker model in the presence of a stiff matter perfect fluid and a negative cosmological constant. We work in the Schutz's variational formalism and the spatial sections have constant negative curvature. We quantize the model and obtain the appropriate Wheeler-DeWitt equation. In this model the states are bounded therefore we compute the discrete energy spectrum and the corresponding eigenfunctions. In the present work, we consider only the negative eigenvalues and their corresponding eigenfunctions. This choice implies that the energy density of the perfect fluid is negative. A stiff matter perfect fluid with this property produces a model with a bouncing solution, at the classical level, free from an initial singularity. After that, we use the eigenfunctions in order to construct wave packets and evaluate the time-dependent expectation value of the scale factor. We find that it oscillates between maximum and minimum values. Since the expectation value of the scale factor never vanishes, we confirm that this model is free from an initial singularity, also, at the quantum level.

scholarly journals Noncommutative cosmological models coupled to a perfect fluid and a cosmological constant

2012 ◽  
Vol 2012 (5) ◽  
Author(s):  
E. M. C. Abreu ◽  
M. V. Marcial ◽  
A. C. R. Mendes ◽  
W. Oliveira ◽  
G. Oliveira-Neto
Keyword(s):  
Cosmological Constant ◽  
Perfect Fluid ◽  
Cosmological Models

scholarly journals Quasilocal conservation laws in cosmology: A first look

2020 ◽  
Vol 29 (14) ◽  
pp. 2043029
Author(s):  
Marius Oltean ◽  
Hossein Bazrafshan Moghaddam ◽  
Richard J. Epp
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Conservation Laws ◽  
Perfect Fluid ◽  
Vacuum Energy ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Stress Energy ◽  
Fluid Matter ◽  
Stress Energy Momentum Tensor

Quasilocal definitions of stress-energy–momentum—that is, in the form of boundary densities (in lieu of local volume densities) — have proven generally very useful in formulating and applying conservation laws in general relativity. In this Essay, we take a basic look into applying these to cosmology, specifically using the Brown–York quasilocal stress-energy–momentum tensor for matter and gravity combined. We compute this tensor and present some simple results for a flat FLRW spacetime with a perfect fluid matter source. We emphasize the importance of the vacuum energy, which is almost universally underappreciated (and usually “subtracted”), and discuss the quasilocal interpretation of the cosmological constant.

scholarly journals Kaluza-Klein FRW cosmological models in Lyra manifold

2009 ◽  
Vol 36 (2) ◽  
pp. 157-166 ◽  
Author(s):  
G. Mohanty ◽  
G.C. Samanta ◽  
K.L. Mahanta
Keyword(s):  
Perfect Fluid ◽  
Displacement Field ◽  
Arbitrary Constant ◽  
Matter Field ◽  
Cosmological Models ◽  
Time Dependent ◽  
Infinite Time ◽  
Lyra Manifold ◽  
Kaluza Klein

We have constructed five dimensional FRW cosmological models for k=-1,1,0 in Lyra manifold with time dependent displacement field. The matter field is considered in the form of a perfect fluid with isotropic matter pressure. It is found that the model for k=-1 is inflationary. For k=1, the model is inflationary for set of values of arbitrary constant n and decelerates in the standard way for another set of values of n. Moreover the concept of Lyra manifold does not exist at infinite time.

scholarly journals SCALAR FIELD COSMOLOGIES WITH PERFECT FLUID IN ROBERTSON-WALKER METRIC

1996 ◽  
Vol 05 (01) ◽  
pp. 71-84 ◽  
Author(s):  
LUIS P. CHIMENTO ◽  
ALEJANDRO S. JAKUBI
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Perfect Fluid ◽  
Cosmological Models ◽  
Asymptotically Stable ◽  
Fluid Source ◽  
Homogeneous Cosmological Models ◽  
Walker Metric ◽  
Stable Solutions

Several isotropic, homogeneous cosmological models containing a self-interacting minimally coupled scalar field, a perfect fluid source and cosmological constant are solved. New exact, asymptotically stable solutions with an inflationary regime or a final Friedmann stage are found for some simple, interesting potentials. It is shown that the fluid and the curvature may determine how these models evolve for large times.

scholarly journals Doubleverse entanglement in third quantized non-minimally coupled varying constants cosmologies

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Adam Balcerzak ◽  
Konrad Marosek
Keyword(s):  
Perfect Fluid ◽  
Gravitational Constant ◽  
Cosmic Strings ◽  
Scalar Fields ◽  
Time Dependent ◽  
Speed Of Light ◽  
The Third ◽  
Varying Constants ◽  
Two Parameters ◽  
Varying Gravitational Constant

Abstract In this paper we consider a third quantized cosmological model with varying speed of light c and varying gravitational constant G both represented by non-minimally coupled scalar fields. The third quantization of such a model leads to a scenario of the doubleverse with the two components being quantum mechanically entangled. We calculate the two parameters describing the entanglement, namely: the energy and the entropy of entanglement where the latter appears to be a proper measure of the entanglement. We consider a possibility that the entanglement can manifests itself as an effective perfect fluid characterized by the time dependent barotropic index $$w_{eff}$$weff, which for some specific case corresponds to the fluid of cosmic strings. It seems that such an entanglement induced effective perfect fluid may generate significant backreaction effect at early times.

scholarly journals Study of Antigravity in an F(R) Model and in Brans-Dicke Theory with Cosmological Constant

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
V. K. Oikonomou ◽  
N. Karagiannakis
Keyword(s):  
Cosmological Constant ◽  
Lagrange Multipliers ◽  
Gravitational Constant ◽  
Time Dependent ◽  
Jordan Frame ◽  
Scalar Tensor Theory ◽  
Initial Model ◽  
Tensor Theory ◽  
Multipliers Method ◽  
Dicke Model

We study antigravity, that is, having an effective gravitational constant with a negative sign, in scalar-tensor theories originating from F(R) theory and in a Brans-Dicke model with cosmological constant. For the F(R) theory case, we obtain the antigravity scalar-tensor theory in the Jordan frame by using a variant of the Lagrange multipliers method and we numerically study the time dependent effective gravitational constant. As we will demonstrate by using a specific F(R) model, although there is no antigravity in the initial model, it might occur or not in the scalar-tensor counterpart, mainly depending on the parameter that characterizes antigravity. Similar results hold true in the Brans-Dicke model.

Sign in / Sign up

Export Citation Format

Share Document