scholarly journals Scale factor dependent equation of state for curvature inspired dark energy, phantom barrier and late cosmic acceleration

2006 ◽  
Vol 643 (1) ◽  
pp. 1-4 ◽  
Author(s):  
S.K. Srivastava
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Scale Factor ◽  
Cosmic Acceleration ◽  
Phantom Barrier

Bouncing scenario in Brans–Dicke theory

2020 ◽  
Vol 17 (04) ◽  
pp. 2050056
Author(s):  
Sunil Kumar Tripathy ◽  
Subingya Pandey ◽  
Alaka Priyadarsini Sendha ◽  
Dipanjali Behera
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Linear Equation ◽  
Scale Factor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Dark Fluid

A bouncing scenario is studied in the framework of generalized Brans–Dicke theory. In order to have a dark energy (DE) driven late time cosmic acceleration, we have considered a unified dark fluid simulated by a linear equation of state (EoS). The evolutionary behavior of the DE equation of parameter derived from the unified dark fluid has been discussed. The effect of the bouncing scale factor on the Brans–Dicke parameter, self-interacting potential and the Brans–Dicke scalar field is investigated.

scholarly journals Unveiling cosmography from the dark energy equation of state

2019 ◽  
Vol 28 (12) ◽  
pp. 1950154 ◽  
Author(s):  
Celia Escamilla-Rivera ◽  
Salvatore Capozziello
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Equation ◽  
Cosmological Parameters ◽  
Cosmic Acceleration ◽  
Type Ia ◽  
State Formula ◽  
Cosmological Tests ◽  
Supernovae Type Ia ◽  
Straightforward Approach

Constraining the dark energy equation of state, [Formula: see text], is one of the main issues of current and future cosmological surveys. In practice, this requires making assumptions about the evolution of [Formula: see text] with redshift [Formula: see text], which can be manifested in a choice of a specific parametric form where the number of cosmological parameters play an important role in the observed cosmic acceleration. Since any attempt to constrain the EoS requires some prior fixing in one form or the other, settling a method to constrain cosmological parameters is of great importance. In this paper, we provide a straightforward approach to show how cosmological tests can be improved via a parametric methodology based on cosmography. Using Supernovae Type IA samplers, we show how by performing a statistical analysis of a specific dark energy parametrization can give directly the cosmographic parameters values.

Inhomogeneous early viscous fluid universe: A concrete model for dark energy

2016 ◽  
Vol 13 (04) ◽  
pp. 1650037
Author(s):  
G. S. Khadekar
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Bulk Viscosity ◽  
Scale Factor ◽  
Inhomogeneous Equation ◽  
Special Choice ◽  
Field Equations ◽  
Dependent Parameter ◽  
Frw Model ◽  
The Universe

In this paper the dynamical equation of the scale factor of the universe is investigated to describe the effect of bulk viscosity on the early evolution of the universe. We assume the inhomogeneous equation of state of the form [Formula: see text], where the adiabatic parameter [Formula: see text] varies with the scale factor [Formula: see text] proposed by Carvalho [Unified description of early universe, Int. J. Theor. Phys. 35 (1996) 2019] and [Formula: see text] is a time-dependent parameter in the framework of the flat FRW model. From this modified equation of state the exact solution of the field equations is obtained by considering the bulk viscosity is a linear combination of two terms of the form: [Formula: see text] and cosmological constant [Formula: see text], where [Formula: see text] and [Formula: see text] are constants, in which an inflationary phase is followed by the radiation dominated phase. For a special choice of the parameter we can explain the dark energy dominant universe and Friedmann equations are solved for two different phases of the universe and obtain the [Formula: see text]–[Formula: see text] relation.

Cosmological implications of Tsallis dark energy in modified Brans–Dicke theory

2019 ◽  
Vol 28 (11) ◽  
pp. 1950146 ◽  
Author(s):  
Abdul Jawad ◽  
Asma Aslam ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Cosmic Acceleration ◽  
Observation Data ◽  
Frw Universe ◽  
Om Diagnostic ◽  
Equation Of State Parameter ◽  
Graphical Presentation

Tsallis entropy has been widely applied to analyze the gravitational and cosmological setups. We discuss the dark energy (DE) model by its cosmological consequences using Tsallis holographic entropy in the framework of modified Brans–Dicke (BD) gravity. We consider the Hubble horizon as infrared cutoff to study the nature of DE that is responsible for current cosmic acceleration. We focus on flat FRW universe in interacting and noninteracting scenarios between DE and dark matter (DM). In this framework, we discuss the cosmological parameters like equation of state parameter, deceleration parameter, Om-diagnostic, squared speed of sound and planes like evolving equation of state parameter and statefinders. We discuss graphical presentation of these parameters and planes. We compare the results with observation data to check the consistency of results.

Scale factor — Cosmic time relation and occurrences of future cosmic singularities with different redshift parametrizations of dark energy EoS-s

2019 ◽  
Vol 34 (28) ◽  
pp. 1950228
Author(s):  
Swetalina Bhowmik ◽  
Ritabrata Biswas
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmic Time ◽  
Scale Factor ◽  
Late Time ◽  
Expanding Universe ◽  
Unknown Parameters ◽  
Time Relation

While modeling our late time cosmically accelerated universe, it is popular to involve different dark energy (DE) models, the equation of state (EoS) of which can be taken as a function of the redshift and some unknown parameters. Barboza and Alcaniz have proposed one such kind of DE EoS model. We use some new parametrizations like Feng, Shen, Li, Li I and II and Polynomial parametrizations to get more accurate concepts about the fate of our expanding universe. We try to find how the hypothesis of the fate of our universe behaves in the above background of DE models. Possibilities of occurrences of future cosmic singularities are studied.

scholarly journals LINEAR DARK ENERGY EQUATION OF STATE REVEALED BY SUPERNOVAE?

2014 ◽  
Vol 29 (02) ◽  
pp. 1450008 ◽  
Author(s):  
VINCENZO SALZANO ◽  
YUN WANG ◽  
IRENE SENDRA ◽  
RUTH LAZKOZ
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Linear Relation ◽  
Energy Equation ◽  
Scale Factor ◽  
Data Set ◽  
Significant Evidence ◽  
Type Ia ◽  
Energy Information ◽  
A Current

In this paper, we propose a test to detect the linearity of the dark energy equation of state, and apply it to the SNLS3 Type Ia Supernova (SN Ia) data set. We find that: (a) current SN Ia data are well described by a dark energy equation of state linear in the cosmic scale factor a, at least up to a redshift z = 1, independent of the pivot points chosen for the linear relation; (b) there is no significant evidence of any deviation from linearity. This apparent linearity may reflect the limit of dark energy information extractable from current SN Ia data.

A new potential for scalar field dark energy

2020 ◽  
Vol 17 (09) ◽  
pp. 2050139
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Hubble Parameter ◽  
Time Derivative ◽  
Field Potential ◽  
State Parameter ◽  
Simple Relation ◽  
Scale Factor ◽  
Equation Of State Parameter

In this paper, we have investigated some cosmological consequences of a quintessence dark energy model. In particular, we have obtained the forms of the equation of state parameter, the deceleration parameter and the field potential by considering a simple relation between the scale factor and the time derivative of the scalar field, instead of assuming any functional form for the scalar field potential or the scale factor or the equation of state parameter. We have found that the model provides the desired early deceleration followed by present acceleration of the universe. The potential derived numerically in this work in the form [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] are real constant parameters. It has also been found that our model mimics as the standard [Formula: see text]CDM model in future. Finally, we have also shown the evolution of the normalized Hubble parameter for our model and the [Formula: see text]CDM model and compared that with the latest Hubble parameter data.

Tsallis holographic dark energy in Bianchi type-III spacetime with scalar fields

2019 ◽  
Vol 34 (37) ◽  
pp. 1950310 ◽  
Author(s):  
Murat Korunur
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Bianchi Type ◽  
Holographic Dark Energy ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Acceleration Phase ◽  
Eos Parameter ◽  
Type Iii

In this paper, we study one of the new dark energy models named Tsallis holographic dark energy (THDE) model considering the Bianchi type-III spacetime model. Considering deceleration parameter, transition from deceleration to acceleration phase happens at [Formula: see text]. The equation of state (EoS) parameter has been found using the Granda–Oliveros (GO) scale. It is found that for [Formula: see text] values, EoS parameter behaves like the quintessence era; for [Formula: see text], EoS parameter behaves like the phantom dark energy and approaches [Formula: see text]CDM model at late-time cosmic acceleration phase. Also, we reconstructed a correspondence between THDE model and some well-known scalar fields, such as tachyon, quintessence and [Formula: see text]-essence. In addition, we evaluated equation of state parameter, kinetic energy and scalar potential versus time.

Bianchi type-III holographic dark energy model with quintessence

2018 ◽  
Vol 15 (09) ◽  
pp. 1850161 ◽  
Author(s):  
M. Vijaya Santhi ◽  
V. U. M. Rao ◽  
Daba Meshesha Gusu ◽  
Y. Aditya
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Bianchi Type ◽  
Holographic Dark Energy ◽  
Scale Factor ◽  
Holographic Dark Energy Model ◽  
The Universe ◽  
Average Scale Factor

In this study, we investigate an anisotropic Bianchi type-[Formula: see text] space-time in the presence of matter and holographic dark energy components within the framework of general relativity. We obtained the solution of the field equations by assuming (i) the expansion scalar [Formula: see text] in the model is proportional to shear scalar [Formula: see text], (ii) hybrid expansion law for average scale factor (keeping an eye on the recent scenario of accelerating nature of the universe). We develop cosmological parameters like deceleration and equation of state parameters. These parameters are plotted versus redshift [Formula: see text] for different values of power component of average scale factor [Formula: see text]. We observe that the equation of state varies in quintessence region ([Formula: see text]) and ultimately tends to [Formula: see text]CDM model ([Formula: see text]). The deceleration parameter exhibits a smooth transition from early decelerated epoch to present accelerated era. In addition, we establish the correspondence between our holographic dark energy model and quintessence scalar field. We also express the self-interacting potential [Formula: see text] and scalar field [Formula: see text] of quintessence model as functions of cosmic time [Formula: see text], which describes the accelerated expansion of the universe.

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