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 GENERALIZED MODEL FOR Λ DARK ENERGY

2009 ◽  
Vol 18 (03) ◽  
pp. 389-396 ◽  
Author(s):  
UTPAL MUKHOPADHYAY ◽  
P. C. RAY ◽  
SAIBAL RAY ◽  
S. B. DUTTA CHOUDHURY
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
A Priori ◽  
State Parameter ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Two Fluid

Einstein field equations under spherically symmetric space–times are considered here in connection with dark energy investigation. A set of solutions is obtained for a kinematic Λ model, viz. [Formula: see text], without assuming any a priori value for the curvature constant and the equation-of-state parameter ω. Some interesting results, such as the nature of cosmic density Ω and deceleration parameter q, have been obtained with the consideration of two-fluid structure instead of the usual unifluid cosmological model.

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 Analytical model of dark energy stars

2020 ◽  
Vol 35 (10) ◽  
pp. 2050071
Author(s):  
Ayan Banerjee ◽  
M. K. Jasim ◽  
Anirudh Pradhan
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Equation ◽  
Vacuum Solution ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Interior Solution ◽  
Field Equations ◽  
Star Models

In this paper, we study the structure and stability of compact astrophysical objects which are ruled by the dark energy equation of state (EoS). The existence of dark energy is important for explaining the current accelerated expansion of the universe. Exact solutions to Einstein field equations (EFE) have been found by considering particularized metric potential, Finch and Skea ansatz. 1 The obtained solutions are relevant to the explanation of compact fluid sphere. Further, we have observed at the junction interface that the interior solution is matched with the Schwarzschild’s exterior vacuum solution. Based on that, we have noticed the obtained solutions are well in agreement with the observed maximum mass bound of [Formula: see text], namely, PSR J1416-2230, Vela X-1, 4U 1608-52, Her X-1 and PSR J1903+327, whose predictable masses and radii are not compatible with the standard neutron star models. Also, the stability of the stellar configuration has been discussed briefly, by considering the energy conditions, surface redshift, compactness, mass-radius relation in terms of the state parameter [Formula: see text]. Finally, we demonstrate that the features so obtained are physically acceptable and consistent with the observed/reported data.[Formula: see text] Thus, the present dark energy equation of state appears talented regarding the presence of several exotic astrophysical matters.

scholarly journals GHOST DARK ENERGY IN f(R) MODEL OF GRAVITY

2012 ◽  
Vol 21 (06) ◽  
pp. 1250057 ◽  
Author(s):  
KH. SAAIDI ◽  
A. AGHAMOHAMMADI ◽  
B. SABET ◽  
O. FAROOQ
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dynamical Evolution ◽  
State Parameter ◽  
Jordan Frame ◽  
Density Parameter ◽  
Eos Parameter ◽  
Phantom Divide ◽  
Equation Of State Parameter ◽  
Phantom Divide Line

We study a correspondence between f(R) model of gravity in the Jordan frame and a phenomenological kind of dark energy (DE), which is known as QCD ghost DE. Since this kind of DE is not stable in the context of Einsteinian theory of gravity and Brans–Dicke model of gravity, we consider two kinds of correspondence between modified gravity and DE. By studding the dynamical evolution of model and finding relevant quantities such as, equation of state parameter, deceleration parameter, dimensionless density parameter, we show that the model can describe the present Universe and also the EoS parameter can cross the phantom divide line without needs to any kinetic energy with negative sign. Furthermore, by obtaining the adiabatic squared sound speed of the model for different cases of interaction, we show that this model is stable. Finally, we fit this model with supernova observational data in a noninteraction case and we find the best values of parameter at 1σ confidence interval as; [Formula: see text], [Formula: see text] and [Formula: see text]. These best-fit values show that DE equation of state parameter, ωd0, can cross the phantom divide line at the present time.

Study of Tsallis, Rényi and Sharma–Mittal holographic dark energies for entropy corrected modified field equations in Hořava–Lifshitz gravity

2020 ◽  
Vol 17 (11) ◽  
pp. 2050170
Author(s):  
Sayani Maity ◽  
Ujjal Debnath
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Cold Dark Matter ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Frw Universe ◽  
Equation Of State Parameter ◽  
The Universe

The purpose of this work is to study the Tsallis, Rényi and Sharma–Mittal holographic dark energy models in order to evaluate the accelerated expansion of the Universe. In this regard, we consider the modified field equations for logarithmic and power law versions of entropy corrected models in FRW Universe filled with interacting dark energy and cold dark matter within the framework of Hořava–Lifshitz gravity. Employing the Nojiri and Odintsov (NO) cut-off as infrared cutoff, we explore the nature of the different cosmological quantities like the equation of state parameter, squared speed of sound and [Formula: see text]–[Formula: see text] cosmological plane during the cosmic evolution. The equation of state parameter shows the different stages of the evolution of the Universe for the considered models. By analyzing the cosmological plane [Formula: see text]–[Formula: see text], we obtain the freezing region for these models. Also, due to the study of squared speed of sound, we show the classically stable behavior of the considered models.

FRW viscous fluid cosmological model with time-dependent inhomogeneous equation of state

2017 ◽  
Vol 15 (01) ◽  
pp. 1830001 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Quadratic Form ◽  
State Parameter ◽  
The Other ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Viscous Models

In this paper, we present two viscous models of non-perfect fluid by avoiding the introduction of exotic dark energy. We consider the first model in terms of deceleration parameter [Formula: see text] has a viscosity of the form [Formula: see text] and the other model in quadratic form of [Formula: see text] of the type [Formula: see text]. In this framework we find the solutions of field equations by using inhomogeneous equation of state of form [Formula: see text] with equation of state parameter [Formula: see text] is constant and [Formula: see text].

scholarly journals Interaction of Bianchi type-I anisotropic cloud string cosmological model universe with electromagnetic field

2020 ◽  
Vol 17 (09) ◽  
pp. 2050133
Author(s):  
Kangujam Priyokumar Singh ◽  
Mahbubur Rahman Mollah ◽  
Rajshekhar Roy Baruah ◽  
Meher Daimary
Keyword(s):  
Electromagnetic Field ◽  
Cosmological Model ◽  
Bianchi Type ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Rest Energy ◽  
Model Universe ◽  
Bianchi Type I ◽  
String Cosmological Model

Here, we have investigated the interaction of Bianchi type-I anisotropic cloud string cosmological model universe with electromagnetic field in the context of general relativity. In this paper, the energy-momentum tensor is assumed to be the sum of the rest energy density and string tension density with an electromagnetic field. To obtain exact solution of Einstein’s field equations, we take the average scale factor as an integrating function of time. Also, the dynamics and significance of various physical parameters of model are discussed.

scholarly journals Dark Energy Stars with Quadratic Equation of State

2019 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Kasmaei
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Condition ◽  
Scalar Fields ◽  
Quadratic Equation ◽  
Accelerated Expansion ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Quadratic Equation Of State

Recent astronomical observations with respect to measurements in distant supernovas, cosmic microwave background and weak gravitational lensing confirm that the Universe is undergoing a phase of accelerated expansion and it has been proposed that this cosmological behavior is caused by a hypothetical dark energy which has a strong negative pressure that allows explain the expanding universe. Several theoretical ideas and models related dark the energy includes the cosmological constant, quintessence, Chaplygin gas, braneworld and tachyonic scalar fields. In this paper, we have obtained new relativistic stellar configurations considering an anisotropic fluid distribution with a charge distribution which could represents a potential model of a dark energy star. In order to investigate the effect of a quadratic equation of state in this anisotropic model we specify particular forms for the gravitational potential that allow solving the Einstein-Maxwell field equations. For these new solutions we checked that the radial pressure, metric coefficients, energy density, anisotropy factor, charge density , mass function are well defined and are regular in the interior of the star. The solutions found can be used in the development of dark energy stars models satisfying all physical acceptability conditions but the causality condition and strong energy condition are violated. We expect that these models have multiple applications in astrophysics and cosmology.

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