scholarly journals Universe Models with a Variable Cosmological “Constant” and a “Big Bounce”

2001 ◽  
Vol 562 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Hongya Liu ◽  
Paul S. Wesson
Keyword(s):  
Cosmological Constant ◽  
Variable Cosmological Constant ◽  
Universe Models ◽  
Big Bounce

scholarly journals ACCELERATING UNIVERSE IN A BIG BOUNCE MODEL

2004 ◽  
Vol 19 (06) ◽  
pp. 449-456 ◽  
Author(s):  
BEILI WANG ◽  
HONGYA LIU ◽  
LIXIN XU
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Early Time ◽  
Accelerating Universe ◽  
Late Time ◽  
Total Energy Density ◽  
Variable Cosmological Constant ◽  
Type Ia ◽  
The Universe ◽  
Big Bounce

Recent observations of Type Ia supernovae provide evidence for the acceleration of our universe, which leads to the possibility that the universe is entering an inflationary epoch. We simulate it under a "big bounce" model, which contains a time variable cosmological "constant" that is derived from a higher dimension and manifests itself in 4D spacetime as dark energy. By properly choosing the two arbitrary functions contained in the model, we obtain a simple exact solution in which the evolution of the universe is divided into several stages. Before the big bounce, the universe contracts from a Λ-dominated vacuum, and after the bounce, the universe expands. In the early time after the bounce, the expansion of the universe is decelerating. In the late time after the bounce, dark energy (i.e. the variable cosmological "constant") overtakes dark matter and baryons, and the expansion enters an accelerating stage. When time tends to infinity, the contribution of dark energy tends to two thirds of the total energy density of the universe, qualitatively in agreement with observations.

scholarly journals ANISOTROPIC COMPACT STARS WITH VARIABLE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 21 (13) ◽  
pp. 1250088 ◽  
Author(s):  
SK. MONOWAR HOSSEIN ◽  
FAROOK RAHAMAN ◽  
JAYANTA NASKAR ◽  
MEHEDI KALAM ◽  
SAIBAL RAY
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Compact Star ◽  
Compact Stars ◽  
Radial Dependence ◽  
Regularity Conditions ◽  
Variable Cosmological Constant ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Surface Redshift

Recently, the small value of the cosmological constant and its ability to accelerate the expansion of the universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose, we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited 4U 1820-30 as a specific example of that kind of star.

scholarly journals Influence of the cosmological constant in closed-universe models containing matter and radiation

1970 ◽  
Vol 66 (2) ◽  
pp. 202-216 ◽  
Author(s):  
A. Agnese ◽  
M. La Camera ◽  
A. Wataghin
Keyword(s):  
Cosmological Constant ◽  
Closed Universe ◽  
Universe Models

scholarly journals Dynamical Chern–Simons modified gravity, Gödel Universe and variable cosmological constant

2010 ◽  
Vol 693 (4) ◽  
pp. 494-497 ◽  
Author(s):  
C. Furtado ◽  
J.R. Nascimento ◽  
A.Yu. Petrov ◽  
A.F. Santos
Keyword(s):  
Cosmological Constant ◽  
Modified Gravity ◽  
Variable Cosmological Constant ◽  
Chern Simons ◽  
Gödel Universe

EARLY HOMOGENEOUS UNIVERSE WITH VARIABLE COSMOLOGICAL CONSTANT: KINEMATICS TESTS

2007 ◽  
Vol 22 (13) ◽  
pp. 2415-2431 ◽  
Author(s):  
C. P. SINGH
Keyword(s):  
Cosmological Constant ◽  
Cosmic Time ◽  
Field Equations ◽  
Variable Cosmological Constant ◽  
Angular Diameter Distance ◽  
Proper Distance ◽  
Inflationary Phase ◽  
Homogeneous Universe ◽  
Gamma Law ◽  
The Look

A spatially homogeneous cosmological model with flat geometry filled with perfect fluid is studied in the presence of a variable cosmological "constant." Einstein's field equations are solved by using the "gamma-law" equation of state p = (γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe with variable cosmological "constant." A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. It has been observed that the solutions are compatible with the result of recent observations. Exact expressions for the look-back time, proper distance, luminosity distance and angular diameter distance versus redshift are derived and their meaning are discussed in detail. The various physical aspects of the models are also discussed.

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