COSMOLOGICAL MODELS OF GLOBAL UNIVERSE EVOLUTION AND DECOMPOSITION OF PERTURBATIONS

2002 ◽  
Vol 17 (29) ◽  
pp. 4451-4456 ◽  
Author(s):  
SERGEI V. CHERVON
Keyword(s):  
Sigma Model ◽  
Cosmological Models ◽  
Linear Sigma Model ◽  
Cosmological Perturbations ◽  
Frw Universe ◽  
Global Evolution ◽  
Two Component ◽  
The Universe ◽  
Universe Evolution ◽  
Friedmann Robertson Walker

It is shown that cosmological models, based on the self-interacting scalar field theory or on the theory of the chiral non-linear sigma model. Can describe the global evolution of the Universe, extending from an inflationary stage to the present time epoch. The method of cosmological perturbations decomposition for inflaton and non-inflaton ones is applied for two-component chiral cosmological model in the spatially flat Friedmann-Robertson-Walker (FRW) Universe. New non-inflaton mode of cosmological perturbations is found.

Transit cosmological models in FRW universe under the two-fluid scenario

2019 ◽  
Vol 16 (01) ◽  
pp. 1950007 ◽  
Author(s):  
Pryanka Garg ◽  
Rashid Zia ◽  
Anirudh Pradhan
Keyword(s):  
Cosmological Models ◽  
Observational Cosmology ◽  
Accelerating Universe ◽  
Frw Universe ◽  
Two Fluids ◽  
Slowing Down ◽  
Two Fluid Scenario ◽  
The Universe ◽  
Two Fluid ◽  
Friedmann Robertson Walker

This paper is an attempt to revisit the Friedmann–Robertson–Walker (FRW) cosmological models under the new scenario of observational cosmology, which has established that the current universe is expanding with an increasing rate, in contrast to the earlier belief that the rate of expansion is constant or slowing down. This paper represents a model which encompasses both, earlier decelerating and the current accelerating universe, passing through a transition phase. The universe is assumed to be filled with two fluids, barotropic and dark energy. We have considered two cases; first, when these fluids are assumed to be non-interacting and second, when they interact with each other. Some physical, kinematic and geometric properties of the model are also discussed along with the acceptability and stability of the solution. The results found are very compatible with the established results as well as recent observations.

scholarly journals The cosmological behavior and the statefinder diagnosis for the New Tsallis agegraphic dark energy

2020 ◽  
Vol 35 (38) ◽  
pp. 2050318
Author(s):  
Umesh Kumar Sharma ◽  
Shikha Srivastava
Keyword(s):  
Dark Energy ◽  
Dynamical Analysis ◽  
Current Phase ◽  
Statefinder Parameters ◽  
Frw Universe ◽  
Eos Parameter ◽  
Agegraphic Dark Energy ◽  
Evolutionary Trajectories ◽  
The Universe ◽  
Friedmann Robertson Walker

In this work, we have considered the recently proposed new Tsallis agegraphic dark energy (NTADE) model [Mod. Phys. Lett. A 34, 1950086 (2019)] within the framework of a flat Friedmann–Robertson–Walker (FRW) Universe by taking various values of the parameter [Formula: see text]. The NTADE model shows the current phase transition of the Universe from decelerated to accelerated phase. The NTADE equation of state (EoS) parameter shows a rich behavior as it can be quintessence-like or phantom-like depending on the value of [Formula: see text]. For discriminating the NTADE model from [Formula: see text]CDM, we have plotted the statefinder parameters [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] pair. The NTADE model shows distinct evolutionary trajectories of their evolution in ([Formula: see text]) and ([Formula: see text]) plane. An analysis using the snap parameter and the [Formula: see text] pair dynamical analysis have also been performed.

The condensation of the matter in the linear sigma model of the two-component mixing system

2019 ◽  
Vol 64 (3) ◽  
pp. 36-44
Author(s):  
Hoa Le Viet ◽  
◽  
Anh Nguyen Tuan ◽  
Hue Dang Thi Minh ◽  
Tam Dinh Thanh ◽  
...  
Keyword(s):  
Sigma Model ◽  
Linear Sigma Model ◽  
Two Component

scholarly journals Unified universe history through phantom extended Chaplygin gas

2016 ◽  
Vol 94 (7) ◽  
pp. 659-670 ◽  
Author(s):  
B. Pourhassan
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Late Time ◽  
Two Component ◽  
Equation Of State Parameter ◽  
Phantom Scalar ◽  
The Universe ◽  
Phantom Scalar Field ◽  
Universe Evolution

The universe evolution from inflation to late-time acceleration is investigated in a unified way, using a two-component fluid constituted from extended Chaplygin gas alongside a phantom scalar field. We extract solutions for the various cosmological eras, focusing on the behavior of the scale factor, the various density parameters and the equation-of-state parameter. Furthermore, we extract and discuss bouncing solutions. Finally, we examine the perturbations of the model, ensuring their stability and extracting the predictions for the tensor-to-scalar ratio.

A unified picture of cosmological entropy on apparent horizon in F(R, G) gravity

2017 ◽  
Vol 32 (33) ◽  
pp. 1750182 ◽  
Author(s):  
Ali İhsan Keskin ◽  
Irfan Acikgoz
Keyword(s):  
Apparent Horizon ◽  
Second Law Of Thermodynamics ◽  
Hawking Temperature ◽  
Second Law ◽  
Field Equations ◽  
Frw Universe ◽  
Generalized Second Law ◽  
History Of ◽  
The Universe ◽  
Friedmann Robertson Walker

In this study, the validity of the generalized second law of thermodynamics (GSLT) has been investigated in F(R, G) gravity. We consider that the boundary of the universe is surrounded by an apparent horizon in the spatially flat Friedmann–Robertson–Walker (FRW) universe, and we take into account the Hawking temperature on the horizons. The unified solutions of the field equations corresponding to gravity theory have been applied to the validity of the GSLT frame, and in this way, both the solutions have been verified and all the expansion history of the universe has been shown in a unified picture.

scholarly journals ENERGY–MOMENTUM IN VISCOUS KASNER-TYPE UNIVERSE IN BERGMANN–THOMSON FORMULATIONS

2005 ◽  
Vol 20 (10) ◽  
pp. 2169-2177 ◽  
Author(s):  
MUSTAFA SALTI ◽  
ALI HAVARE
Keyword(s):  
Total Energy ◽  
Space Time ◽  
Cosmological Models ◽  
Energy And Momentum ◽  
Momentum Complex ◽  
The Universe ◽  
Friedmann Robertson Walker

Using the Bergmann–Thomson energy–momentum complex and its tele-parallel gravity version, we obtain the energy and momentum of the universe in viscous Kasner-type cosmological models. The energy and momentum components (due to matter plus field) are found to be zero and this agree with a previous work of Rosen and Johri et al. who investigated the problem of the energy in Friedmann–Robertson–Walker universe. The result that the total energy and momentum components of the universe in these models is zero supports the viewpoint of Tryon. Rosen found that the energy of the Friedmann–Robertson–Walker space–time is zero, which agrees with the studies of Tryon.

scholarly journals Inflation in terms of a viscous van der Waals coupled fluid

2018 ◽  
Vol 15 (09) ◽  
pp. 1850150 ◽  
Author(s):  
I. Brevik ◽  
V. V. Obukhov ◽  
A. V. Timoshkin
Keyword(s):  
Van Der Waals ◽  
Accelerated Expansion ◽  
Frw Universe ◽  
Slow Roll ◽  
Analytic Expressions ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Gravitational Equations ◽  
Friedmann Robertson Walker ◽  
Planck Satellite

We propose to describe the acceleration of the universe by introducing a model of two coupled fluids. We focus on the accelerated expansion at the early stages. The inflationary expansion is described in terms of a van der Waals equation of state for the cosmic fluid, when account is taken of bulk viscosity. We assume that there is a weak interaction between the van der Waals fluid and the second component (matter). The gravitational equations for the energy densities of the two components are solved for a homogeneous and isotropic Friedmann–Robertson–Walker (FRW) universe, and analytic expressions for the Hubble parameter are obtained. The slow-roll parameters, the spectral index, and the tensor-to-scalar ratio are calculated and compared with the most recent astronomical data from the Planck satellite. Given reasonable restriction on the parameters, the agreement with observations is favorable.

FRW universe in f(R,T) gravity

2021 ◽  
pp. 2150104
Author(s):  
R. K. Tiwari ◽  
D. Sofuoğlu ◽  
A. Beesham
Keyword(s):  
Phase Transition ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Field Equations ◽  
Frw Universe ◽  
Expansion Phase ◽  
Age Of The Universe ◽  
The Universe ◽  
Modified Theory ◽  
Friedmann Robertson Walker

In this study, Friedmann–Robertson–Walker space-time filled with a perfect fluid in [Formula: see text] modified theory, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the energy–momentum tensor of matter, has been considered. The investigation of the phase transition of the universe from the decelerating expansion phase to the accelerating one has been made by adopting a special form of the varying deceleration parameter that is inversely proportional to the Hubble parameter. The exact solution of the field equations has been derived. The kinematic and dynamical quantities of the model have been obtained and their evolutions have been discussed by means of their graphs. The statefinder diagnostic has been used and the age of the universe has been computed for testing the validity of the model. It has been shown that the dominant energy of the model is ordinary matter which behaves as the SCDM model at the beginning and it is a quintessence like fluid which behaves as the [Formula: see text]CDM model at late times.

scholarly journals THE MINIMAL CURVATURE OF THE UNIVERSE IN MODIFIED GRAVITY AND CONFORMAL ANOMALY RESOLUTION OF THE INSTABILITIES

2004 ◽  
Vol 19 (08) ◽  
pp. 627-638 ◽  
Author(s):  
SHIN'ICHI NOJIRI ◽  
SERGEI D. ODINTSOV
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Cosmic Acceleration ◽  
Conformal Anomaly ◽  
Frw Universe ◽  
Conformal Fields ◽  
Acceleration Of The Universe ◽  
Minimal Curvature ◽  
The Universe ◽  
Universe Evolution

We discuss the modified gravity which may produce the current cosmic acceleration of the universe and eliminate the need for dark energy. It is shown that such models where the action quickly grows with the decrease of the curvature define the FRW universe with the minimal curvature. Infinite time is required to reach the minimal curvature during the universe evolution. It is demonstrated that quantum effects of conformal fields may strongly suppress the instabilities discovered in modified gravity. We also briefly speculate on the modification of gravity combined with the presence of the cosmological constant dark energy.

scholarly journals THERMODYNAMIC OF THE GHOST DARK ENERGY UNIVERSE

2012 ◽  
Vol 27 (31) ◽  
pp. 1250182 ◽  
Author(s):  
CHAO-JUN FENG ◽  
XIN-ZHOU LI ◽  
XIAN-YONG SHEN
Keyword(s):  
Dark Energy ◽  
Vacuum Energy ◽  
Hawking Temperature ◽  
Frw Universe ◽  
Energy Component ◽  
Ghost Dark Energy ◽  
Dark Energy Component ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

Recently, the vacuum energy of the QCD ghost in a time-dependent background is proposed as a kind of dark energy candidate to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter H, which is the Hawking temperature on the Hubble horizon of the Friedmann–Robertson–Walker (FRW) Universe. In this paper, we generalized this model and chose the Hawking temperature on the so-called trapping horizon, which will coincide with the Hubble temperature in the context of flat FRW Universe dominated by the dark energy component. We study the thermodynamics of Universe with this kind of dark energy and find that the entropy-area relation is modified, namely, there is another new term besides the area term.

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