Transit dark energy string cosmological models with perfect fluid in F(R,T)-gravity

2018 ◽  
Vol 15 (10) ◽  
pp. 1850168 ◽  
Author(s):  
Rashid Zia ◽  
Dinesh Chandra Maurya ◽  
Anirudh Pradhan
Keyword(s):  
Dark Energy ◽  
Early Time ◽  
Momentum Tensor ◽  
Late Time ◽  
Field Equations ◽  
Accelerating Expansion ◽  
Type Ia ◽  
Dynamical Parameters ◽  
The Stability ◽  
The Universe

In this paper, spatially homogeneous and anisotropic Bianchi type-[Formula: see text] dark energy (DE) cosmological transit models with string fluid source in [Formula: see text] gravity [T. Harko et al., Phys. Rev. D 84 (2011) 024020], where [Formula: see text] is the Ricci scalar and [Formula: see text] the trace of the stress energy–momentum tensor, have been studied in the context of early time decelerating and late-time accelerating expansion of the Universe as suggested by the recent observations. The exact solutions of the field equations are obtained first by using generalized hybrid expansion law (HEL) [Formula: see text] which yields a time-dependent deceleration parameter [Formula: see text] and second by considering the metric coefficient [Formula: see text]. By using recent constraints from supernovae type-Ia union data [Cunha, arXiv:0811.2379[astro-ph]], we obtain [Formula: see text] and [Formula: see text] for transit model [Formula: see text]. The Universe has an initial singularity and is anisotropic closed and it tends to be flat at the late time, i.e. our Universe is in accelerating expansion. Our model shows a phase transition property from decelerating to accelerating. It is remarkable to mention here that our Universe is homogeneous and anisotropic in the early phase whereas it becomes homogeneous and isotropic for [Formula: see text]. We have also discussed the stability of the background solution with respect to perturbations of the metric along with the properties of future singularities in the Universe dominated by DE including the phantom-type fluid. Various physical and dynamical parameters are also calculated and investigated in terms of time and redshift both.

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.

Phase transition of LRS Bianchi type-I cosmological model in f(R,T) gravity

2020 ◽  
Vol 17 (12) ◽  
pp. 2050187
Author(s):  
R. K. Tiwari ◽  
D. Sofuoğlu ◽  
V. K. Dubey
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Early Time ◽  
Momentum Tensor ◽  
Late Time ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Accelerating Expansion ◽  
Acceleration Of The Universe

In this work, LRS Bianchi type-I cosmological model with perfect fluid source in [Formula: see text] gravity theory, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the stress energy-momentum tensor, has been studied in order to investigate early time deceleration and late time acceleration of the universe. By proposing a new special form of time-varying deceleration parameter in terms of Hubble parameter, the exact solution of the field equations has been obtained. The physical and geometric quantities of the model have been derived and their evolution has been discussed. Our model has an initial singularity and initially exhibits decelerating expansion and transits to accelerating expansion phase at last eras. The nature of the matter source of the model is consistent with the standard model in frame of the structure formation.

scholarly journals Accelerating cosmology in modified gravity: From convenient F(R) or string-inspired theory to bimetric F(R) gravity

2014 ◽  
Vol 11 (02) ◽  
pp. 1460006 ◽  
Author(s):  
Shin'ichi Nojiri ◽  
Sergei D. Odintsov
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Early Time ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Reconstruction Method ◽  
Free Theory ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Unified Description

We consider modified gravity which may describe the early-time inflation and/or late-time cosmic acceleration of the universe. In particular, we discuss the properties of F(R), F(G), string-inspired and scalar-Einstein–Gauss–Bonnet gravities, including their FRW equations and fluid or scalar-tensor description. Simplest accelerating cosmologies are investigated and possibility of unified description of the inflation with dark energy is described. The cosmological reconstruction program which permits to get the requested universe evolution from modified gravity is developed. As some extension, massive F(R) bigravity which is ghost-free theory is presented. Its scalar-tensor form turns out to be the easiest formulation. The cosmological reconstruction method for such bigravity is presented. The unified description of inflation with dark energy in F(R) bigravity turns out to be possible.

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.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
Author(s):  
P.K. SAHOO ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

A five dimensional Kaluza-Klein space time is considered with wet dark fluid (WDF) source in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D \textbf{84}, 024020, (2011)). A new equation of state in the form of WDF has been used for dark energy (DE) component of the universe. It is modeled on the equation of state p=\omega(\rho-\rho^*) which can be describing a liquid, for example water. The exact solutions to the corresponding field equations are obtained for power law and exponential law of the volumetric expansion. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and the very late time of the universe. This model obtained here shows that even in the presence of wet dark fluid, the universe indicates accelerated expansion of the universe.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
pp. 1062-1067 ◽  
Author(s):  
P. K. Sahoo ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

In this paper, we have investigated the five-dimensional Kaluza–Klein space time with wet dark fluid (WDF), which is a candidate for dark energy (DE), in the framework of f(R, T) gravity. R and T denote the Ricci scalar and the trace of the energy–momentum tensor, respectively (Harko et al. Phys. Rev. D, 84, 024020 (2011)). We have used equation of state in the form of WDF for the DE component of the universe. It is modeled on the equation of state p = ω(ρ – ρ*). With the help of the power law and exponential law of volumetric expansion, we have derived the exact solutions of the corresponding field equations. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and very late time of the universe. It is concluded that the model obtained here shows that even in the presence of WDF, the universe indicates accelerated expansion of the universe.

scholarly journals Kantowski–Sachs Tsallis holographic dark energy model with sign-changeable interaction

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Y. Sobhanbabu ◽  
M. Vijaya Santhi
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Deceleration Parameter ◽  
Graphical Representation ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Field Equations ◽  
Dynamical Parameters ◽  
Frame Work ◽  
The Stability

AbstractIn this work devoted to the investigation of the Tsallis holographic dark energy (IR cut-off is Hubble radius) in homogeneous and anisotropic Kantowski–Sachs Universe within the frame-work of Saez–Ballester scalar tensor theory of gravitation. We have constructed non-interacting and interacting Tsallis holographic dark energy models by solving the field equations using the relationship between the metric potentials. This relation leads to a viable deceleration parameter model which exhibits a transition of the Universe from deceleration to acceleration. In interacting case, we focus on sign-changeable interaction between Tsallis holographic dark energy and dark matter. The dynamical parameters like equation of state parameter, energy densities of Tsallis holographic dark energy and dark matter, deceleration parameter, and statefinder parameters of the models are explained through graphical representation. And also, we discussed the stability analysis of the our models.

scholarly journals ACCELERATING DARK ENERGY MODELS IN BIANCHI TYPE-V SPACETIME

2011 ◽  
Vol 26 (30) ◽  
pp. 2261-2275 ◽  
Author(s):  
ANIRUDH PRADHAN ◽  
HASSAN AMIRHASHCHI
Keyword(s):  
Dark Energy ◽  
Bianchi Type ◽  
Late Time ◽  
Field Equations ◽  
Future Evolution ◽  
New Exact Solutions ◽  
Spatially Homogeneous ◽  
Type V ◽  
The Universe ◽  
Bianchi Type V

Some new exact solutions of Einstein's field equations in a spatially homogeneous and anisotropic Bianchi type-V spacetime with minimally interaction of perfect fluid and dark energy components have been obtained. To prevail the deterministic solution we choose the scale factor [Formula: see text], which yields a time-dependent deceleration parameter (DP), representing a model which generates a transition of the universe from the early decelerating phase to the recent accelerating phase. We find that for n ≥ 1, the quintessence model is reproducible with present and expected future evolution of the universe. The other models (for n < 1), we observe the phantom scenario. The quintessence as well as phantom models approach to isotropy at late time. For different values of n, we can generate a class of physically viable DE models. The cosmic jerk parameter in our descended model is also found to be in good concordance with the recent data of astrophysical observations under appropriate condition. The physical and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed.

scholarly journals Ghost Dark Energy in the DGP Braneworld

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi
Keyword(s):  
Dark Energy ◽  
Sound Speed ◽  
State Parameter ◽  
Late Time ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Stability ◽  
The Universe ◽  
Dgp Braneworld

We investigate the ghost model of dark energy in the framework of DGP braneworld. We explore the cosmological consequences of this model by determining the equation of state parameter, ωD, the deceleration, and the density parameters. We also examine the stability of this model by studying the squared of the sound speed in the presence/absence of interaction term between dark energy and dark matter. We find out that in the absence of interaction between two dark sectors of the universe we have ωD→-1 in the late time, while in the presence of interaction ωD can cross the phantom line -1. In both cases the squared of sound speed vs2 does not show any signal of stability. We also determine the statefinder diagnosis of this model as well as the ωD-ωD′ plane and compare the results with the ΛCDM model. We find that ωD-ωD′ plane meets the freezing region in the absence of interaction between two dark sectors, while it meets both the thawing and the freezing regions in the interacting case.

BULK VISCOUS BRANS–DICKE COSMOLOGICAL MODELS AND LATE-TIME ACCELERATION OF THE UNIVERSE

2003 ◽  
Vol 12 (05) ◽  
pp. 925-939 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Energy Density ◽  
Momentum Tensor ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Bulk Viscous ◽  
Order Of Magnitude ◽  
Viscous Pressure ◽  
The Universe ◽  
Matter Energy

We consider the dynamics of a causal bulk viscous cosmological fluid filled flat homogeneous Universe in the framework of the Brans–Dicke theory. Three classes of exact solutions of the field equations are obtained and the behavior of the physical parameters is considered in detail. In this model the energy density associated to the Brans–Dicke scalar field is of the same order of magnitude as the matter energy density. The inclusion of the bulk viscous pressure term in the matter energy-momentum tensor leads to a non-decelerating evolution of the Universe.

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