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.

scholarly journals GRAVITATIONAL LENSING STATISTICS AS A PROBE OF DARK ENERGY

2000 ◽  
Vol 15 (16) ◽  
pp. 1023-1029 ◽  
Author(s):  
ZONG-HONG ZHU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Cosmological Model ◽  
Gravitational Lensing ◽  
Mass Density ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Analytic Expression ◽  
Cosmic Mass

By using the comoving distance, we derive an analytic expression for the optical depth of gravitational lensing, which depends on the redshift to the source and the cosmological model characterized by the cosmic mass density parameter Ωm, the dark energy density parameter Ωm and its equation of state ωx = px/ρx. It is shown that, the larger the dark energy density and the more negative its pressure, the higher is the gravitational lensing probability. This fact can provide an independent constraint for dark energy.

scholarly journals Non-Extensive Thermodynamics Effects in the Cosmology of f(T) Gravity

Symmetry ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 75
Author(s):  
Asmaa G. Shalaby ◽  
Vasilis K. Oikonomou ◽  
Gamal G. L. Nashed
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Energy Equation ◽  
State Parameter ◽  
Gravitational Theory ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Equation Of State Parameter ◽  
Relativistic Matter

Using f(T) gravitational theory, we construct modified cosmological models via the first law of thermodynamics by using the non-extensive thermodynamics framework, the effects of which are captured by the parameter δ. The resulting cosmological equations are modified compared to the standard Einstein-Hilbert ones, with the modifications coming from the f(T) gravitational theory and from the non-extensive parameter which quantifies the non-extensive thermodynamics effects quantified by the parameter δ, which when is set equal to unity, one recovers the field equations of f(T) gravity. We study in detail the cosmological evolution of the model in the presence of collisionless non-relativistic matter case, and we derive the exact forms of the dark energy density parameter and of the dark energy equation of state parameter, from which we impose constraints on the non-extensive thermodynamics parameter, δ, by using the Planck 2018 data on cosmological parameters. Accordingly, we repeat our calculations after including the relativistic matter along with the non-relativistic one, and we derive the new forms of the dark energy density parameter and of the dark energy equation of state parameter. Our study shows that the inclusion of non-extensive thermodynamic effects, quantified by the parameter δ, for a flat Friedmann-Robertson-Walker Universe, has measurable differences compared with the normal thermodynamics case. We confront our results with Type Ia supernovae observations for z≥0.4 and we obtain reasonably agreement with the observational data.

scholarly journals PARAMETRIZATION OF THE DARK ENERGY EQUATION OF STATE

2007 ◽  
Vol 16 (10) ◽  
pp. 1581-1591 ◽  
Author(s):  
VINOD B. JOHRI ◽  
P. K. RATH
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Comparative Study ◽  
Energy Equation ◽  
Critical Evaluation ◽  
Density Parameter ◽  
Dark Energy Density ◽  
History Of ◽  
The Universe

A comparative study of various parametrizations of the dark energy equation of state is made. Astrophysical constraints from LSS, CMB and BBN are laid down to test the physical viability and cosmological compatibility of these parametrizations. A critical evaluation of the four-index parametrizations reveals that Hannestad–Mörtsell as well as Lee parametrizations are simple and transparent in probing the evolution of the dark energy during the expansion history of the universe and they satisfy the LSS, CMB and BBN constraints on the dark energy density parameter.

Chaplygin scalar field reconstruction of the modified ghost dark energy model

2015 ◽  
Vol 93 (8) ◽  
pp. 855-861
Author(s):  
Kayoomars Karami
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Energy Density ◽  
Dark Energy Model ◽  
State Parameter ◽  
Energy Model ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Ghost Dark Energy

Within the framework of Einstein gravity, we establish a correspondence between the Chaplygin scalar field model and the modified ghost dark energy model. We consider a spatially non-flat Friedmann–Robertson–Walker universe containing modified ghost dark energy and dark matter that are in interaction with each other. We solve the differential equation governing the dimensionless modified ghost dark energy density parameter numerically. Then we obtain the evolutionary behaviors of both the energy density and equation of state parameters of the modified ghost dark energy. More interesting is that the equation of state parameter at the present time can cross the phantom divide line provided the interaction parameter b2 > 0.15 is compatible with the observations. Furthermore, we reconstruct both the Chaplygin gas scalar field and potential according to the evolutionary behavior of the modified ghost dark energy model.

Holographic dark energy in a vector field cosmology

2015 ◽  
Vol 12 (10) ◽  
pp. 1550119 ◽  
Author(s):  
S. Davood Sadatian
Keyword(s):  
Dark Energy ◽  
Vector Field ◽  
Equation Of State ◽  
Energy Density ◽  
Holographic Dark Energy ◽  
Lorentz Invariance ◽  
Holographic Model ◽  
Dark Energy Density ◽  
Invariance Violation ◽  
Lorentz Invariance Violation

We obtain interacting holographic dark energy density in the framework of vector field cosmology (LIV). We consider possible modification of equation of state for the holographic energy density in lorentz invariance violation cosmology. In this case we select Jeans length as the IR cut-off in the holographic model. Then we consider the interaction between holographic energy densities ρΛ and ρm in this framework.

scholarly journals CAN THE EXISTENCE OF DARK ENERGY BE DIRECTLY DETECTED?

2009 ◽  
Vol 24 (18n19) ◽  
pp. 3426-3436 ◽  
Author(s):  
MARTIN L. PERL
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Total Mass ◽  
Mass Density ◽  
Mass Energy ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
Expansion Of The Universe ◽  
The Universe

Over the last decade, astronomical observations show that the acceleration of the expansion of the universe is greater than expected from our understanding of conventional general relativity, the mass density of the visible universe, the size of the visible universe and other astronomical measurements. The additional expansion has been attributed to a variety of phenomenon that have been given the general name of dark energy. Dark energy in the universe seems to comprise a majority of the energy in the visible universe amounting to about three times the total mass energy. But locally the dark energy density is very small. However it is not zero. In this paper I describe the work of others and myself on the question of whether dark energy density can be directly detected. This is a work-in-progress and I have no answer at present.

scholarly journals Tsallis holographic model of dark energy: Cosmic behavior, statefinder analysis and ωD–ωD′ pair in the nonflat universe

2019 ◽  
Vol 28 (15) ◽  
pp. 1950164 ◽  
Author(s):  
Vipin Chandra Dubey ◽  
Umesh Kumar Sharma ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Density Parameter ◽  
Holographic Model ◽  
Spatial Curvature ◽  
Present Value ◽  
Evolutionary Trajectories

This paper investigates the Tsallis holographic dark energy (THDE) model in accordance with the apparent horizon as an infrared cut-off, in a non flat universe. The cosmological evolution of the deceleration parameter and equation of state of THDE model are calculated. The evolutionary trajectories are plotted for the THDE model for distinct values of the Tsallis parameter [Formula: see text] besides distinct spatial curvature contributions, in the statefinder [Formula: see text] parameter-pairs and [Formula: see text] plane, considering the present value of dark energy (DE) density parameter [Formula: see text], [Formula: see text], in the light of [Formula: see text] observational data. The statefinder and [Formula: see text] plane plots specify the feature of the THDE and demonstrate the separation between this framework and other models of DE.

scholarly journals Viscous generalized Chaplygin gas interacting with f(R,T) gravity

2017 ◽  
Vol 14 (04) ◽  
pp. 1750051 ◽  
Author(s):  
E. H. Baffou ◽  
M. J. S. Houndjo ◽  
I. G. Salako
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Graphical Representation ◽  
Input Parameter ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Generalized Chaplygin Gas ◽  
Accelerating Expansion

In this paper, we study in Friedmann–Robertson–Walker universe the interaction between the viscous generalized Chaplygin gas with [Formula: see text] gravity, which is an arbitrary function of the Ricci scalar [Formula: see text] and the trace [Formula: see text] of the energy–momentum tensor. Assuming that the contents of universe are dominated by a generalized Chaplygin gas and dark energy, we obtained the modified Friedmann equations and also the time-dependent energy density and pressure of dark energy due to the shear and bulk viscosities for three interacting models depending on an input parameter [Formula: see text]. Within the simple form of scale factor (power-law), we discuss the graphical representation of dark energy density parameter and investigate the shear and bulk viscosities effects on the accelerating expansion of the universe for each interacting model.

scholarly journals A Study on Ricci Dark Energy in Bulk-Brane Interaction

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Surajit Chattopadhyay
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Power Law ◽  
Ricci Dark Energy ◽  
Dark Energy Density ◽  
Evolution Of The Universe ◽  
The Impact ◽  
The Universe ◽  
Matter Fields

We have investigated the effects of the interaction between a brane universe and the bulk in which it is embedded. Considering the effects of the interaction between a brane universe and the bulk, we have obtained the equation of state for the interacting holographic Ricci dark energy density ρΛ=3c2(H˙+2H2) in the flat universe. We have investigated the impact of c2 on the equation of state ωΛ. Also, considering the power law for of the scale factor, we have observed that nontrivial contributions of dark energy which differ from the standard matter fields confined to the brane are increasing with the evolution of the universe.

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