scholarly journals TIME VARIABLE COSMOLOGICAL CONSTANT OF HOLOGRAPHIC ORIGIN WITH INTERACTION IN BRANS–DICKE THEORY

2012 ◽  
Vol 21 (01) ◽  
pp. 1250005 ◽  
Author(s):  
JIANBO LU ◽  
LINA MA ◽  
MOLIN LIU ◽  
YABO WU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Deceleration Parameter ◽  
Diagnostic Method ◽  
Time Variable ◽  
Accelerating Universe ◽  
Variable Cosmological Constant ◽  
Phantom Divide ◽  
Jerk Parameter

Time variable cosmological constant (TVCC) of holographic origin with interaction in Brans–Dicke theory is discussed in this paper. We investigate some characters for this model, and show the evolutions of deceleration parameter and equation of state (EOS) for dark energy. It is shown that in this scenario an accelerating universe can be obtained and the evolution of EOS for dark energy can cross over the boundary of phantom divide. In addition, a geometrical diagnostic method, jerk parameter, is applied to this model to distinguish it with cosmological constant.

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 DARK ENERGY WITH DARK SPINORS

2010 ◽  
Vol 25 (02) ◽  
pp. 101-110 ◽  
Author(s):  
CHRISTIAN G. BÖHMER ◽  
JAMES BURNETT
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Time Frame ◽  
Accelerating Universe ◽  
Phantom Divide ◽  
The Past ◽  
Big Rip ◽  
Reasonable Time Frame ◽  
Spinor Model ◽  
The Universe

Ever since the first observations that we are living in an accelerating universe, it has been asked what dark energy is. There are various explanations, all of which have various drawbacks or inconsistencies. Here we show that using a dark spinor field it is possible to have an equation of state that crosses the phantom divide, becoming a dark phantom spinor which evolves into dark energy. This type of equation of state has been mildly favored by experimental data, however, in the past there were hardly any theories that satisfied this crossing without creating ghosts or causing a singularity which results in the universe essentially ripping. The dark spinor model converges to dark energy in a reasonable time frame avoiding the big rip and without attaining negative kinetic energy as it crosses the phantom divide.

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 A Magnetized Dark Energy Type R/W Model with Polytropic Equation of State in Brans-Dicke Theory

2020 ◽  
Vol 12 (3) ◽  
pp. 251-257
Author(s):  
M. Dewri
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Variable Cosmological Constant ◽  
Volumetric Expansion ◽  
Dynamical Behaviors ◽  
Tensor Theory ◽  
Polytropic Equation ◽  
Theory Of Gravitation ◽  
Energy Type ◽  
Physical Quantities

In this paper, we study the spatially homogeneous Robertson-Walker cosmological models with magnetized isotropic dark energy like fluid in the scalar-tensor theory of gravitation proposed by Brans-Dicke. Variable cosmological constant ᴧ and Polytropic equation of state have been used to find exact solutions of the models with volumetric expansion and power-law relation. The Physical and dynamical behaviors of the models have been discussed using some physical quantities like energy density, pressure, and coefficient of bulk viscosity.

Anisotropic Dark Energy Cosmological Model with Cosmic Strings

2020 ◽  
Author(s):  
T. Vinutha ◽  
V.U.M. Rao ◽  
Molla Mengesha
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Eos Parameter ◽  
Phantom Divide

The present study deals with a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type-I dark energy cosmological model containing one dimensional cosmic string fluid source. The Einstein's field equations are solved by using a relation between the metric potentials and hybrid expansion law of average scale factor. We discuss accelerated expansion of our model through equation of state (ωde) and deceleration parameter (q). We observe that in the evolution of our model, the equation of state parameter starts from matter dominated phase ωde > -1/3 and ultimately attains a constant value in quintessence region (-1 < ωde < -1/3). The EoS parameter of the model never crosses the phantom divide line (ωde = 1). These facts are consistent with recent observations. We also discuss some other physical parameters.

scholarly journals Analysis off(R)Theory Corresponding to NADE and NHDE

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
M. Sharif ◽  
M. Zubair
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Future Evolution ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Effective Description

We develop the connection off(R)theory with new agegraphic and holographic dark energy models. The functionf(R)is reconstructed regarding thef(R)theory as an effective description for these dark energy models. We show the future evolution offand conclude that these functions represent distinct pictures of cosmological eras. The cosmological parameters such as equation of state parameter, deceleration parameter, statefinder diagnostic, andw−w′analysis are investigated which assure the evolutionary paradigm off.

scholarly journals THEORETICAL ASPECTS OF QUINTOM MODELS

2010 ◽  
Vol 25 (11n12) ◽  
pp. 909-921 ◽  
Author(s):  
TAOTAO QIU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Early Universe ◽  
Dark Energy Model ◽  
Phenomenological Study ◽  
Energy Model

Quintom models, with its Equation of State being able to cross the cosmological constant boundary w = -1, turns out to be attractive for phenomenological study. It can not only be applicable for dark energy model for current universe, but also lead to a bounce scenario in the early universe.

scholarly journals DARK ENERGY IN GLOBAL BRANE UNIVERSE

2007 ◽  
Vol 16 (10) ◽  
pp. 1633-1640 ◽  
Author(s):  
YONGLI PING ◽  
LIXIN XU ◽  
CHENGWU ZHANG ◽  
HONGYA LIU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Exact Solutions ◽  
Deceleration Parameter ◽  
Mass Density ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Friedmann Equations

We discuss the exact solutions of brane universes and the results indicate that the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain that the new term varies with the redshift z. Finally, the evolutions of the mass density parameter Ω2, dark energy density parameter Ωx and deceleration parameter q2 are studied.

DARK MATTER AND DARK ENERGY - FACT OR FANTASY?

2004 ◽  
Vol 19 (31) ◽  
pp. 5333-5333
Author(s):  
PHILIP MANNHEIM
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Einstein Gravity ◽  
Fine Tuning ◽  
Accelerating Universe ◽  
Conformal Invariant ◽  
Invariant Metric ◽  
Conformal Theory

We show that the origin of the dark matter and dark energy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the global induced one which is effective for cosmology being altogether weaker than the local induced one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then it is not the cosmological constant which is quenched but rather the amount of gravity that it produces.

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