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.

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 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.

Anisotropic minimally interacting dark energy models with cosmic strings and a massive scalar field

2021 ◽  
Author(s):  
M. P. V. V. Bhaskara Rao ◽  
Y. Aditya ◽  
U. Y. Divya Prasanthi ◽  
D. R. K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Massive Scalar Field ◽  
Anisotropic Dark Energy

This paper deals with the construction of locally rotationally symmetric (LRS) Bianchi type-II (B-II) cosmological models obtained by solving Einstein field equations coupled with an attractive massive scalar field (MSF) when the source of gravitation is the mixture of cosmic string cloud and anisotropic dark energy (DE) fluid which are minimally interacting. We have obtained exact cosmological models by using (i) shear scalar is proportional to the scalar expansion of the space–time and (ii) a power-law relation between the average scale factor of the universe and the scalar field. Our models represent string cosmological model and DE model in the presence of MSF. Using our model, we determine cosmological parameters such as energy densities, deceleration parameter, statefinders and equation of state parameter. We, also, present the tension density and energy density of the string. We discuss the physical aspects of these cosmological parameters. It is observed that our models represent accelerated expansion phenomenon of our universe as confirmed by Supernova Ia experiment.

scholarly journals Barrow holographic dark energy with hubble horizon as IR cutoff

2020 ◽  
Vol 18 (01) ◽  
pp. 2150014
Author(s):  
Shikha Srivastava ◽  
Umesh Kumar Sharma
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Density Parameter ◽  
Eos Parameter ◽  
History Of ◽  
Hubble Horizon ◽  
Flrw Universe ◽  
The Stability

In this work, we propose a non-interacting model of Barrow holographic dark energy (BHDE) using Barrow entropy in a spatially flat FLRW Universe considering the IR cutoff as the Hubble horizon. We study the evolutionary history of important cosmological parameters, in particular, deceleration parameter, equation of state (EoS) parameter, the BHDE and matter density parameter, and also observe satisfactory behaviors in the BHDE model. The stability of the BHDE model has been examined by squared sound speed [Formula: see text]. In addition, to describe the accelerated expansion of the Universe, the correspondence of the BHDE model with the quintessence scalar field has been reconstructed.

scholarly journals REQUIRED CONDITIONS FOR LATE TIME ACCELERATION AND EARLY TIME DECELERATION IN GENERALIZED SCALAR–TENSOR THEORIES

2003 ◽  
Vol 18 (04) ◽  
pp. 651-671 ◽  
Author(s):  
L. M. DIAZ-RIVERA ◽  
LUIS O. PIMENTEL
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Cosmological Parameters ◽  
Early Time ◽  
Weak Field ◽  
Scale Factor ◽  
Coupling Function ◽  
Accelerated Expansion ◽  
Late Time ◽  
Cosmological Constants

We consider a generalized scalar–tensor theory, where we let the coupling function ω(ϕ) and the effective cosmological constants Λ(ϕ) be undetermined. We obtain general expressions for ω(ϕ) and Λ(ϕ) in terms of the scalar field and the scale factor, and show that ω(ϕ) depends on the scalar field and the scale factor in a complicated way. In order to study the conditions for an accelerated expansion at the present time and a decelerated expansion in the past, we assume a power law evolution for the scalar field and the scale factor. We analyze the required conditions that allow our model to satisfy the weak field limits on ω(ϕ), and at the same time, to obtain the correct values of cosmological parameters, as the energy density Ωm0 and cosmological constant Λ(t0). We also study the conditions for a decelerated expansion at an early time dominated by radiation. We find values for ω(ϕ) and Λ(ϕ) consistent with the expectations of a where the cosmological constant decreases with the time and the coupling function increases until the values are accepted today.

Entropy corrected holographic dark energy models in modified gravity

2017 ◽  
Vol 26 (04) ◽  
pp. 1750040 ◽  
Author(s):  
Abdul Jawad ◽  
Nadeem Azhar ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Cold Dark Matter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Second Law Of Thermodynamics ◽  
Accelerated Expansion ◽  
Eos Parameter ◽  
Generalized Second Law ◽  
Expansion Of The Universe

We consider the power law and the entropy corrected holographic dark energy (HDE) models with Hubble horizon in the dynamical Chern–Simons modified gravity. We explore various cosmological parameters and planes in this framework. The Hubble parameter lies within the consistent range at the present and later epoch for both entropy corrected models. The deceleration parameter explains the accelerated expansion of the universe. The equation of state (EoS) parameter corresponds to quintessence and cold dark matter ([Formula: see text]CDM) limit. The [Formula: see text] approaches to [Formula: see text]CDM limit and freezing region in both entropy corrected models. The statefinder parameters are consistent with [Formula: see text]CDM limit and dark energy (DE) models. The generalized second law of thermodynamics remain valid in all cases of interacting parameter. It is interesting to mention here that our results of Hubble, EoS parameter and [Formula: see text] plane show consistency with the present observations like Planck, WP, BAO, [Formula: see text], SNLS and nine-year WMAP.

Cosmological study in loop quantum cosmology through dark energy model

2017 ◽  
Vol 26 (02) ◽  
pp. 1750007
Author(s):  
Abdul Jawad ◽  
Shamaila Rani ◽  
Ines G. Salako ◽  
Faiza Gulshan
Keyword(s):  
Dark Energy ◽  
Quantum Cosmology ◽  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
Loop Quantum Cosmology ◽  
Eos Parameter ◽  
Pilgrim Dark Energy ◽  
Expansion Of The Universe

The interacting generalized ghost version of pilgrim dark energy (GGPDE) is discussed in the framework of loop quantum cosmology (LQC). We analyze the behavior of cosmological parameters (Hubble, equation of state (EoS), deceleration) and cosmological planes ([Formula: see text] and [Formula: see text]-[Formula: see text]) in the present scenario ([Formula: see text] represents the EoS parameter and [Formula: see text] indicates the evolution of the EoS parameter, [Formula: see text],[Formula: see text] are statefinder parameters). It is observed that the deceleration parameter corresponds to the accelerated expansion of the universe. The EoS parameter lies in vacuum and phantom regions for all cases of [Formula: see text] (pilgrim dark energy (PDE) parameter). The [Formula: see text] plane lies in thawing region for all cases of [Formula: see text]. The [Formula: see text] plane corresponds to [Formula: see text] cold dark matter (CDM) and Chaplygin gas model. We have also mentioned the constraints on calculated cosmological parameters and found that all the trajectories of cosmological parameters and planes show the consistence behavior with the observational schemes.

Tsallis holographic dark energy models in axially symmetric space time

2020 ◽  
Vol 17 (01) ◽  
pp. 2050011 ◽  
Author(s):  
Vipin Chandra Dubey ◽  
Ambuj Kumar Mishra ◽  
Shikha Srivastava ◽  
Umesh Kumar Sharma
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Holographic Dark Energy ◽  
Field Potential ◽  
Accelerated Expansion ◽  
Anisotropic Universe ◽  
Axially Symmetric ◽  
Eos Parameter ◽  
Quintessence Field ◽  
The Universe

In this work, we have examined the behavior of Bianchi-I (axially symmetric) matter-dominated and the anisotropic Universe with the proposed dark energy, Tsallis holographic dark energy (THDE), with the Hubble horizon as infrared cut-off [Tavayef et al., Tsallis holographic dark energy, Phys. Lett. B 781 (2018) 195–200]. The Universe evolution from matter-dominated epoch to dark energy dominated epoch is described by our proposed THDE model. The EoS parameter in our THDE model explains the evolution of the Universe according to the value of nonextensive or Tsallis parameter [Formula: see text], phantom era ([Formula: see text]) or quintom (phantom line crossing) and the quintessence era ([Formula: see text]), before reaching to completely dark energy-dominated era in the future. Additionally, we also plan to reconcile the dark energy by the method of reconstructing the evolution of the scalar field potential. For the analysis, we take into account the quintessence field and phantom scalar field for this reconstruction, which at present shows the accelerated expansion.

Kantowski–Sachs universe with dark energy fluid and massive scalar field

2020 ◽  
Vol 98 (11) ◽  
pp. 993-998
Author(s):  
K. Deniel Raju ◽  
M.P.V.V. Bhaskara Rao ◽  
Y. Aditya ◽  
T. Vinutha ◽  
D.R.K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Massive Scalar Field ◽  
Anisotropic Dark Energy ◽  
Expansion Of The Universe ◽  
The Universe

This study is mainly concerned with a spatially homogeneous and anisotropic Kantowski–Sachs cosmological model with anisotropic dark energy fluid and massive scalar field. We solve the field equations using (i) the shear scalar proportionality to the expansion scalar and (ii) a mathematical condition that is a consequence of the power law between the scalar field and the average scale factor of the universe, and the corresponding dark energy model is presented. The cosmological parameters of the model are computed and discussed, as well as the relevance of its dynamical aspects to the recent scenario of the accelerated expansion of the universe.

Rényi holographic dark energy in the Brans–Dicke cosmology

2020 ◽  
Vol 35 (34) ◽  
pp. 2050281
Author(s):  
Umesh Kumar Sharma ◽  
Vipin Chandra Dubey
Keyword(s):  
Dark Energy ◽  
Stability Analysis ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Density Parameter ◽  
Eos Parameter ◽  
Hubble Horizon ◽  
The Stability

In this paper, we construct a holographic dark energy (HDE) model considering the IR cut-off as Hubble horizon, holographic hypothesis, and using the generalized Rényi entropy, and investigate its cosmological outcomes in Brans–Dicke gravity without interaction. We observe the suitable behavior for the cosmological parameters, involving the deceleration parameter, the equation of state (EoS) parameter, and the density parameter in both flat and non-flat Universes. It is also concluded by the stability analysis that the Rényi holographic dark energy (RHDE) model is classically stable at present and future for the Rényi parameter [Formula: see text] in both flat and non-flat Universe.

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