scholarly journals Time Dependence of Various Cosmological Parameters in the Framework of Kaluza-Klein Space-Time

2019 ◽  
pp. 211-220
Author(s):  
Sudipto Roy ◽  
Anirban Sarkar ◽  
Pritha Ghosh
Keyword(s):  
Cosmological Constant ◽  
Time Dependence ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Field Equations ◽  
Eos Parameter ◽  
Klein Theory ◽  
Time Variations ◽  
Kaluza Klein

A theoretical model, regarding the time dependence of several cosmological parameters, has been constructed in the present study, in the framework of Kaluza-Klein theory, using its field equations for a spatially flat metric. Time dependent empirical expressions of the cosmological constant and the equation of state (EoS) parameter have been substituted into the field equations to determine the time dependence of various cosmological parameters. Time variations of these parameters have been shown graphically. The cosmological features obtained from this model are found to be in agreement with the observed characteristics of the accelerating universe. Interestingly, the signature flipping of the deceleration parameter, from positive to negative, is predicted by this model, indicating a transformation of the universe from a state of decelerated expansion to accelerated expansion, as obtained from astrophysical observations. Time dependence of the gravitational constant (G), energy density (?), cosmological constant (?) and the EoS parameter (?) have been determined and depicted graphically in the present study.

Kaluza–Klein minimally interacting dark energy model in the presence of massive scalar field

2021 ◽  
Vol 36 (08) ◽  
pp. 2150054
Author(s):  
K. Dasu Naidu ◽  
Y. Aditya ◽  
R. L. Naidu ◽  
D. R. K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Eos Parameter ◽  
Massive Scalar Field ◽  
The Universe ◽  
Kaluza Klein

In this paper, our purpose is to discuss the dynamical aspects of Kaluza–Klein five-dimensional cosmological model filled with minimally interacting baryonic matter and dark energy (DE) in the presence of an attractive massive scalar field. We obtain a determinate solution of the Einstein field equations using (i) a relation between the metric potentials and (ii) a power law relation between the average scale factor of the universe and the massive scalar field. We have determined scalar field, matter energy density, DE density, equation of state (EoS) [Formula: see text], deceleration [Formula: see text] and statefinder [Formula: see text] parameters of our model. We also develop [Formula: see text]–[Formula: see text] phase, squared sound speed, statefinders and [Formula: see text]–[Formula: see text] planes in the evolving universe. It is observed that the EoS parameter exhibits quintom-like behavior from quintessence to phantom epoch by crossing the vacuum era of the universe. The squared speed of sound represents the instability of the model, whereas the [Formula: see text]–[Formula: see text] plane shows both thawing and freezing regions. The [Formula: see text]CDM limit is attained in both [Formula: see text]–[Formula: see text] and statefinder planes. We have also discussed the cosmological importance of the above parameters with reference to modern cosmology. It is found that the dynamics of these cosmological parameters indicate the accelerated expansion of the universe which is consistent with the current cosmological observations.

scholarly journals Time Dependence of Cosmological Parameters in the Framework of Brans-Dicke Theory

2019 ◽  
pp. 242-254
Author(s):  
Sudipto Roy ◽  
Avik Ghosh ◽  
Adrika Dasgupta
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Time Dependence ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Scale Factor ◽  
Accelerated Expansion ◽  
Eos Parameter ◽  
Expansion Time ◽  
Time Variations

In the framework of Brans-Dicke (BD) theory of gravitation, the time dependence of some cosmological parameters have been determined in the present study, for an universe having a FRW space-time with zero spatial curvature. The time variations of the energy density, BD parameter, equation of state (EoS) parameter have been determined, from the field equations of the BD theory, in the initial part of this model. For this purpose, we have used ansatzes relating the scalar field with the scale factor and also linking the BD parameter with the scalar field. For these calculations, an empirical expression for the scale factor has been used. This scale factor has been so chosen that it leads to a signature flip of the deceleration parameter from positive to negative in the course of its evolution with time, indicating a change of phase from decelerated expansion to accelerated expansion. Time dependence of the density parameters for matter and dark energy has also been studied here. Using their expressions we have determined the time dependence of the densities of matter and dark energy. The time variations of all these parameters have been shown graphically. Apart from them, we have also shown the variations of the deceleration parameter and the BD parameter as functions of the scalar field graphically.

scholarly journals THE COSMOLOGICAL CONSTANT PROBLEM AND KALUZA–KLEIN THEORY

2001 ◽  
Vol 10 (06) ◽  
pp. 905-912 ◽  
Author(s):  
PAUL S. WESSON ◽  
HONGYA LIU
Keyword(s):  
Field Theory ◽  
General Relativity ◽  
Energy Density ◽  
Cosmological Constant ◽  
Field Equations ◽  
Cosmological Constant Problem ◽  
Klein Theory ◽  
Kaluza Klein

We present technical results which extend previous work and show that the cosmological constant of general relativity is an artefact of the reduction to 4D of 5D Kaluza–Klein theory (or 10D superstrings and 11D supergravity). We argue that the distinction between matter and vacuum is artificial in the context of ND field theory. The concept of a cosmological "constant" (which measures the energy density of the vacuum in 4D) should be replaced by that of a series of variable fields whose sum is determined by a solution of ND field equations in a well-defined manner.

scholarly journals Physical Acceptability of the Renyi, Tsallis and Sharma-Mittal Holographic Dark Energy Models in the f(T,B) Gravity under Hubble’s Cutoff

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 67
Author(s):  
Salim Harun Shekh ◽  
Pedro H. R. S. Moraes ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Two Fluids ◽  
Gravitational Field Equations ◽  
Energy Models ◽  
Different Types ◽  
The Universe

In the present article, we investigate the physical acceptability of the spatially homogeneous and isotropic Friedmann–Lemâitre–Robertson–Walker line element filled with two fluids, with the first being pressureless matter and the second being different types of holographic dark energy. This geometric and material content is considered within the gravitational field equations of the f(T,B) (where T is the torsion scalar and the B is the boundary term) gravity in Hubble’s cut-off. The cosmological parameters, such as the Equation of State (EoS) parameter, during the cosmic evolution, are calculated. The models are stable throughout the universe expansion. The region in which the model is presented is dependent on the real parameter δ of holographic dark energies. For all δ≥4.5, the models vary from ΛCDM era to the quintessence era.

scholarly journals DARBOUX CLASS OF COSMOLOGICAL FLUIDS WITH TIME-DEPENDENT ADIABATIC INDICES

2000 ◽  
Vol 15 (15) ◽  
pp. 979-990 ◽  
Author(s):  
H. C. ROSU
Keyword(s):  
Mathematical Method ◽  
Cosmological Constant ◽  
Time Dependence ◽  
Adiabatic Index ◽  
Time Dependent ◽  
Accelerating Universe ◽  
Constant Parameter ◽  
Darboux Transformations ◽  
Scale Factors ◽  
Experimental Findings

A one-parameter family of time-dependent adiabatic indices is introduced for any given type of cosmological fluid of constant adiabatic index by a mathematical method belonging to the class of Darboux transformations. The procedure works for zero cosmological constant at the price of introducing a new constant parameter related to the time dependence of the adiabatic index. These fluids can be the real cosmological fluids that are encountered at cosmological scales and they could be used as a simple and efficient explanation for the recent experimental findings regarding the present day accelerating universe. In addition, new types of cosmological scale factors, corresponding to these fluids, are presented.

COSMOLOGICAL SOLUTIONS AND THEIR EFFECTIVE PROPERTIES OF MATTER IN KALUZA-KLEIN THEORY

1994 ◽  
Vol 03 (03) ◽  
pp. 627-637 ◽  
Author(s):  
HONGYA LIU ◽  
PAUL S. WESSON
Keyword(s):  
Globular Clusters ◽  
Effective Properties ◽  
Plane Waves ◽  
Big Bang ◽  
Field Equations ◽  
Fifth Dimension ◽  
Cosmological Solutions ◽  
Klein Theory ◽  
The Universe ◽  
Kaluza Klein

We derive a “wave-like” class of exact cosmological solutions of the apparently empty 5D Kaluza-Klein field equations. Here by “wave-like” we mean that the solutions look like plane waves propagating in the fifth dimension. In the interpretation that the fifth dimension in Kaluza-Klein theory may induce matter in four dimensions, we then calculate the effective energy density ρ and pressure p, and study in detail the case for which the equation of state is p=γρ (where γ is an arbitrary constant). We show that for both the matter-dominated (γ=0) and radiation-dominated (γ=1/3) eras of the universe, the 4D spacetime defined by hypersurfaces of the 5D metrics are just the same as those of the standard Friedmann-Robertson-Walker models of general relativity. However, in our models the big bang is like a shock wave propagating along the fifth dimension, and different observers can measure different ages for the universe. This property may be tested using the spread in ages of astrophysical objects such as globular clusters.

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.

Wormhole in 5D Kaluza–Klein cosmology

2017 ◽  
Vol 32 (07) ◽  
pp. 1750023 ◽  
Author(s):  
Gargi Biswas ◽  
B. Modak
Keyword(s):  
Boundary Conditions ◽  
Cosmological Constant ◽  
Dimensional Reduction ◽  
Dimensional Space ◽  
Field Equations ◽  
Positive Cosmological Constant ◽  
Euclidean Field ◽  
Pure Gravity ◽  
Imaginary Field ◽  
Kaluza Klein

We present wormhole as a solution of Euclidean field equations as well as the solution of the Wheeler–deWitt (WD) equation satisfying Hawking–Page wormhole boundary conditions in (4 + 1)-dimensional Kaluza–Klein cosmology. The wormholes are considered in the cases of pure gravity, minimally coupled scalar (imaginary) field and with a positive cosmological constant assuming dynamical extra-dimensional space. In above cases, wormholes are allowed both from Euclidean field equations and WD equation. The dimensional reduction is possible.

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.

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