A Theoretical Study of the Cosmic Expansion in the Framework of Brans-Dicke Theory

Roy, Sudipto

doi:10.9790/4861-0803030412

Cited by 4 publications

(10 citation statements)

References 41 publications

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“…In these two figures we find to become more and more negative with time, at a gradually decreasing rate. Figures 1 and 2 show that the negative values of are more consistent with the requirement expressed by equation (20). According to equations (8) and (19), a negative value of means a decrease of scalar field ( ) with time or equivalently an increase in gravitational constant with time.…”

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confidence: 62%

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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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confidence: 62%

“…According to equations (8) and (19), a negative value of means a decrease of scalar field ( ) with time or equivalently an increase in gravitational constant with time. There are several studies that show a decrease of scalar field with time [14,[17][18][19][20].…”

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confidence: 99%

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

Roy¹

2017

IJAR

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“…5) has been chosen on the basis of some previous studies on Brans-Dicke theory of gravitation [13,14,18]. The empirical expression of BD parameter (eqn.…”

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confidence: 99%

“…For this purpose, empirical expressions of the scale factor ( ), and have been assumed. 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]. Here has been chosen as a function of , in accordance with the requirement of generalized BD theory.…”

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confidence: 99%

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A Model of Time Dependent Equation-of-State Parameter in the Framework of Brans-Dicke Theory

Roy

2017

IJCRR

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Abstract:The characteristics of a time varying equation-of-state (EoS) parameter have been determined on the basis of a simple model, using Brans-Dicke (BD) field equations for an isotropic and homogeneous universe of spatial curvature zero. The scale factor, scalar field and the dimensionless BD parameter have been represented by empirical expressions assumed for the present study. The scale factor has been so chosen that it would generate a time dependent deceleration parameter that shows a signature flip, indicating a change of phase from deceleration to acceleration. Expressions, representing the time dependence of the density of matter, EoS parameter and the BD parameter, have been derived. The nature of time dependence of all these cosmological parameters have been found to depend upon an empirically chosen constant parameter whose value governs the dependence of the scalar field upon the scale factor. For larger values of this parameter, the EoS parameter increases with time approaching a constant negative value and, for more negative values of that constant parameter the EoS parameter decreases with time at a gradually decreasing rate. There are cases where the density of matter initially increases with time to attain a peak value before beginning to fall at a gradually decreasing rate.

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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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A Theoretical Study of the Cosmic Expansion in the Framework of Brans-Dicke Theory

Abstract: On the basis of an assumption of inter-conversion of matter and dark energy, a theoretical model

Cited by 4 publications

References 41 publications

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

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

A Model of Time Dependent Equation-of-State Parameter in the Framework of Brans-Dicke Theory

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

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