Time Evolution of Various Cosmological Parameters and Their Inter-Dependence in the Framework of Brans-Dicke Theory

Roy, Sudipto

doi:10.9790/5728-1203072735

Cited by 3 publications

(16 citation statements)

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“…Nordtvedt proposed a more useful form of this theory which can predict these observations [17,18]. In the generalized form of BD theory, the dimensionless BD parameter ( ) is regarded as a function of the scalar field ( ), and thus it should be regarded as a function of time [18].…”

Section: Introductionmentioning

confidence: 99%

“…For this purpose, empirical expressions for the scale factor, scalar field and the BD parameter have been used. The scale factor has been chosen in a manner such that it generates a time dependent deceleration parameter that changes sign with time, from positive to negative, indicating a transition of the expanding universe from a phase of deceleration to acceleration, as per several recent observations [13,18]. As a step towards generalization, a linear combination of the two field equations has been taken and the ratio of the corresponding constant coefficients has been varied to see its effect on the time dependence of the EoS parameter.…”

Section: Introductionmentioning

confidence: 99%

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Time Dependence of Density Parameters for a Variable EoS Parameter in Brans-Dicke Framework

Roy¹

2017

IOSR JAP

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time Dependence of Density Parameters for a Variable EoS Parameter in Brans-Dicke Framework

Roy¹

2017

IOSR JAP

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“…Using equation (19), one may determine the value of the parameter from the experimental values of and ( ̇ ) . This parameter controls the rate of change of with time.…”

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confidence: 99%

“…The value of should be so chosen that |( ̇ ) | (Weinberg, 1972) [15]. Therefore, using equation (19), one may express this requirement as | | taking .…”

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A Study of the Time Variation of Brans-Dicke Parameter (Ω)

Roy¹

2017

IJAR

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The explicit dependence of the dimensionless Brans-Dicke (BD) parameter ( ) upon time and also upon the equation of state (EoS) parameter (γ) has been determined, by solving BD field equations for a space of zero curvature and also the wave equation for the scalar field (φ). Empirical expressions of the scale factor and the scalar field have been used for this purpose. Dependence of the present value of the BD parameter ( ) upon a parameter controlling the time variation of the scalar field has been obtained and shown graphically. Time variation of the BD parameter, for different values of the EoS parameter, characterizing cosmological eras, has been depicted graphically.Copy Right, IJAR, 2016, All rights reserved. …………………………………………………………………………………………………….... Introduction:-It has been confirmed by high precision observational data and their interpretations that the universe has been expanding with acceleration [1]. This accelerated expansion is said to be caused and controlled by an entity, known as dark energy, whose true nature has not yet been determined. In theoretical calculations, this dark energy is often represented by the cosmological constant (Λ), found in General Relativity (GR). Although it accounts for the experimental observations quite well, it has its own limitations [2]. A large number of alternative theoretical models have emerged to explain gravitational observations. The strengths as well as weaknesses of these models can be found in scientific literature [3]. Non-minimally coupled scalar field theories, particularly in the framework of Brans-Dicke (BD) theory, have been found to be highly useful in explaining the phenomenon of accelerated expansion, although they have failed to explain local astronomical experiments. A quintessence scalar field in BD theory has been shown to generate an accelerated expansion of the universe [4]. Introducing a potential term in BD theory, which is a function of BD scalar field, also allows one to predict an accelerated expansion of the universe [5]. There are major shortcomings of these models. Contrary to the recent observations and theoretical requirements, these models show the matter dominated universe to have an ever accelerating expansion [6,7]. The dimensionless parameter ω in BD theory plays a very important role in the prediction of observational results. The local astronomical observations are explained very well by GR and demands a high (a few hundreds) value of ω [8]. In several models in BD theory, the accelerated expansion is found to be generated by a small value of ω, typically of the order of unity. A study has shown that if an interaction of BD scalar field with dark matter is taken into consideration, a generalized BD theory predicts an accelerated expansion even with a high value of ω [9]. In all these studies, either the BD theory is changed to suit the present requirement or a quintessence scalar field is used to generate sufficient acceleration. Only an interaction between the BD scalar field and the dark matter was used to explain obs...

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A Study of the Time Evolution of Brans-Dicke Parameter and its Role in Cosmic Expansion

Roy

Chowdhury²

2017

IJCRR

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The dependence of Brans-Dicke (BD) parameter upon the scalar field, for different cosmological era of the expanding universe, has been explored. The time dependence of the scalar field has been determined and thereby the explicit time dependence of the BD parameter has been obtained. Experimental observations regarding the time dependence of the gravitational constant has been considered for this study. The scale factor, Hubble parameter, deceleration parameter, matter density, gravitational constant and the density parameters for matter and dark energy have been expressed in terms of the BD parameter and its time derivatives, showing its role in cosmic expansion. for matter and dark energy. PACS Numbers: 98.80.Jk, 95.30.Sf, 95.30.Ft, 91.10.Op, 95.36.+x

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Time Evolution of Various Cosmological Parameters and Their Inter-Dependence in the Framework of Brans-Dicke Theory

Cited by 3 publications

References 13 publications

Time Dependence of Density Parameters for a Variable EoS Parameter in Brans-Dicke Framework

Time Dependence of Density Parameters for a Variable EoS Parameter in Brans-Dicke Framework

A Study of the Time Variation of Brans-Dicke Parameter (Ω)

A Study of the Time Evolution of Brans-Dicke Parameter and its Role in Cosmic Expansion

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