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.

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.

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.

scholarly journals Accelerating dark energy cosmological model in two fluids with hybrid scale factor

2017 ◽  
Vol 14 (09) ◽  
pp. 1750124 ◽  
Author(s):  
B. Mishra ◽  
P. K. Sahoo ◽  
Pratik P. Ray
Keyword(s):  
Dark Energy ◽  
Late Phase ◽  
Scale Factor ◽  
Accelerating Universe ◽  
Late Time ◽  
Field Equations ◽  
Geometrical Properties ◽  
Two Fluids ◽  
The Universe

In this paper, we have investigated the anisotropic behavior of the accelerating universe in Bianchi V spacetime in the framework of General Relativity (GR). The matter field we have considered is of two non-interacting fluids, i.e. the usual string fluid and dark energy (DE) fluid. In order to represent the pressure anisotropy, the skewness parameters are introduced along three different spatial directions. To achieve a physically realistic solutions to the field equations, we have considered a scale factor, known as hybrid scale factor, which is generated by a time-varying deceleration parameter. This simulates a cosmic transition from early deceleration to late time acceleration. It is observed that the string fluid dominates the universe at early deceleration phase but does not affect nature of cosmic dynamics substantially at late phase, whereas the DE fluid dominates the universe in present time, which is in accordance with the observations results. Hence, we analyzed here the role of two fluids in the transitional phases of universe with respect to time which depicts the reason behind the cosmic expansion and DE. The role of DE with variable equation of state parameter (EoS) and skewness parameters, is also discussed along with physical and geometrical properties.

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.

Friedmann–Robertson–Walker (FRW) cosmological model in the present perspective

2019 ◽  
Vol 97 (6) ◽  
pp. 588-595 ◽  
Author(s):  
G.K. Goswami
Keyword(s):  
Cosmological Model ◽  
Perfect Fluid ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
State Parameter ◽  
Accelerating Universe ◽  
Frw Cosmological Model ◽  
The Universe ◽  
Friedmann Robertson Walker

In this paper, we have presented a cosmological model that represents spatially homogenous and isotropic accelerating universe from the perspective of the latest developments begun by Perlmutter and Riess in cosmology. For this, Friedmann–Robertson–Walker (FRW) space–time metric is considered and our universe is assumed to be filled with two types of fluids. One is ordinary baryonic perfect fluid and the other one is mysterious and bizarre dark energy perfect fluid with negative pressure. This creates a repulsive field that produces acceleration in the universe. We have used 581 Union 2.1 compilation data to statistically estimate present values of cosmological parameters Ωde, Ωm, Ωk and equation of state parameter ωde for our model. We have used 31 datasets of observed values of Hubble constant for various redshifts to estimate the present value of Hubble constant H0. On the basis of these we have calculated the present age of the universe, densities, and deceleration parameter. Evolution of deceleration parameter shows that our universe has gone through an accelerating phase two times. In the beginning, and at present. We have also calculated Particle horizon and the time at which acceleration began. Our results are close to latest surveys.

scholarly journals Generalized entropies and corresponding holographic dark energy models

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
H. Moradpour ◽  
A. H. Ziaie ◽  
M. Kord Zangeneh
Keyword(s):  
Black Holes ◽  
Dark Energy ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Tsallis Entropy ◽  
Accelerating Universe ◽  
Frw Universe ◽  
Energy Models ◽  
Generalized Entropies ◽  
The Universe

Abstract Using Tsallis statistics and its relation with Boltzmann entropy, the Tsallis entropy content of black holes is achieved, a result in full agreement with a recent study (Mejrhit and Ennadifi in Phys Lett B 794:24, 2019). In addition, employing Kaniadakis statistics and its relation with that of Tsallis, the Kaniadakis entropy of black holes is obtained. The Sharma-Mittal and Rényi entropy contents of black holes are also addressed by employing their relations with Tsallis entropy. Thereinafter, relying on the holographic dark energy hypothesis and the obtained entropies, two new holographic dark energy models are introduced and their implications on the dynamics of a flat FRW universe are studied when there is also a pressureless fluid in background. In our setup, the apparent horizon is considered as the IR cutoff, and there is not any mutual interaction between the cosmic fluids. The results indicate that the obtained cosmological models have (i) notable powers to describe the cosmic evolution from the matter-dominated era to the current accelerating universe, and (ii) suitable predictions for the universe age.

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