Models In Brans-Dicke Theory Research Articles

Cosmic Aspects of Sharma-Mittal Holographic Dark Energy Model in Brans-Dicke Theory of Gravity

We investigate the cosmological scenario involving spatially homogeneous and anisotropic Bianchi type-V I0 space-time in the context of the Sharma-Mittal holographic dark energy model within the framework of Brans-Dicke’s theory of gravitation. In order to achieve this objective, the Hubble, deceleration, equation-of-state parameters have been discussed. The deceleration parameter (q) is used to measure the pace at which the expansion of the universe is accelerating. The equation-of-state parameter (ωsmhde) characterizes the quintessence and vacuum areas of the universe. All the parameters demonstrate consistent behaviour following the Planck 2018 data. We assess the dynamical stability by defining the squared speed of sound and examining its behaviour. In addition, the energy conditions and the variation of ωsmhde and ω′smhde in the model indicate the present accelerating expansion of the universe.

Brans–Dicke cosmology with cosmological term [formula omitted

In this paper, we study the dynamics of a flat Friedmann–Lemaître–Robertson–Walker (FLRW) cosmological model by considering varying vacuum energy density (VED) in Brans–Dicke (BD) cosmology. For this purpose, we consider the well-motivated VED of the form Λ(H)=c0+3νH2, where c0 and ν are dimensionless constants. We first adopt a theoretical method to find the exact solutions for various cosmological parameters of two models, namely ΛRG1 and ΛRG2. In ΛRG1 model, the scale factor evolves as a power-law expansion which gives the deceleration parameter a constant value. Hence, this type of model does not show the transition phase. The second model ΛRG2 describes the transition phase from deceleration to acceleration. In the second part, we perform two joint likelihood analysis in order to find the constrain on the main free parameters of the ΛRG2 model using the latest observational data sets including SNe Pantheon, H(z) data, BAO/CMB data and local H0 by SH0ES. Performing the two different combination of datasets, we find that the model shows prior decelerated epoch followed by late time accelerated epoch. We also compare the decaying VED with traditional Λ cosmology, which help us to define the evolution of the VED model. The results show that varying VED model in BD theory is consistent with data and the cosmic evolutions are in good agreement with the concordance ΛCDM and BD with constant Λ models. The AIC and BIC selection criteria are also discussed.

Constraining the time-varying vacuum energy models in Brans-Dicke theory

Constraining the time-varying vacuum energy models in Brans-Dicke theory

Observational data analysis for generalized cosmic Chaplygin gas in the background of Brans–Dicke theory

In this paper, we have considered the generalized cosmic Chaplygin gas (GCCG) in the background of Brans–Dicke (BD) theory and also assumed that the Universe is filled in GCCG, dark matter and radiation. To investigate the data fitting of model parameters, we have constrained the model using recent observations. Using [Formula: see text] minimum test, the best-fit values of the model parameters are determined by OHD+CMB+BAO+SNIa joint data analysis. We have drawn the contour figures for different confidence levels [Formula: see text], [Formula: see text] and [Formula: see text]. To examine the viability of the GCCG model in BD theory, we have also determined △AIC and △BIC using the information criteria (AIC and BIC). Graphically, we have analyzed the natures of the equation of state parameter and deceleration parameter for our best-fit values of model parameters. Also, we have studied the square speed of sound [Formula: see text] which lies in the interval [Formula: see text] for expansion of the Universe. So, our considered model is classically stable by considering the best-fit values of the model parameters due to the data analysis.

Anisotropic dark energy models in Brans Dicke theory of gravitation with different expansion laws: A comparative study

In this paper, we have derived the general solutions of the field equations of the Scalar–Tensor theory of gravitation, proposed by Brans and Dicke (1961) within the framework of a locally rotationally symmetric (LRS) metric. We have discussed the anisotropic dark energy models by assuming the time-dependent general scale factor [Formula: see text]. Further, we have discussed the physical and geometric behaviors of the model using different forms of the scale factors. We have also performed a comparative study of the results obtained in various cases. We have observed that the solutions obtained using Hybrid Expansion Law (HEL) are more consistent with recent observations as compared to the rest. Stability of the solutions is also compared using metric perturbations.

Probing bulk viscous matter-dominated model in Brans-Dicke theory

We explore a matter-dominated model with bulk viscosity in Brans-Dicke theory to interpret the observed cosmic accelerating expansion phenomena. We obtain the exact solution of the field equations by taking constant bulk viscous coefficient (which potentially could explain the present accelerated expansion of the Universe) and Brans-Dicke scalar field proportional to some power of the scale factor. The model is studied statistically using the available astronomical data and then compare using the tools taken from information criterion. Using the best-fit values of model parameters we find that the model shows transition from decelerated phase to accelerated phase. The effective equation of state parameter is within the quintessence region ($-1\leq \omega <0$). Thus, the model shows quintessence behavior and approaches to $\varLambda $CDM model in late time. It does not cross the phantom divide line and hence it is free from big-rip singularity. The viscous model also alleviates the age problem. We discuss two diagnostic parameters, namely statefinder and $Om(z)$ and compare the model with the existing models by plotting the trajectories. We also apply Akaike information criterion $(\mathit{AIC})$ and Bayesian information criterion $(\mathit{BIC})$ to discriminate the viscous model based on the penalization associated to the number of parameters. The analyses based on the $\mathit{AIC}$ indicates that there is less support for the viscous model when compared to the $\varLambda $CDM model, while those based on the $\mathit{BIC}$ indicates that there is strong evidence against it in favor of the $\varLambda $CDM model.

Dynamics of axially symmetric anisotropic modified holographic Ricci dark energy model in Brans-Dicke theory of gravitation

In this paper, we have derived field equations of Brans-Dicke (Phys. Rev. 124, 925 (1961)) theory of gravitation with the help of an axially symmetric anisotropic Bianchi-type space-time in the presence of dark matter and anisotropic modified holographic Ricci dark energy. We have presented a cosmological model solving the field equations. We have used i) the hybrid expansion law, ii) a relation between metric potentials and iii) the modified holographic Ricci dark energy defined by Chen and Jing (Phys. Lett. B 679, 144 (2009)) to solve the field equations. We have determined the cosmological parameters, namely, EoS parameter, matter energy density, anisotropic dark energy density, Skewness parameter, deceleration and jerk parameters. A detailed physical discussion of these dynamical parameters is presented through a graphical representation. We observe that we have a quintessence model which exhibits a smooth transition from decelerated phase to an accelerated phase of the universe. This situation is quite in agreement with the scenario of modern cosmology.

A new holographic dark energy model in Brans-Dicke theory with logarithmic scalar field

We study a holographic dark energy model in the framework of Brans-Dicke (BD) theory with taking into account the interaction between dark matter and holographic dark energy. We use the recent observational data sets, namely SN Ia compressed Joint Light-Analysis(cJLA) compilation, Baryon Acoustic Oscillations (BAO) from BOSS DR12 and the Cosmic Microwave Background (CMB) of Planck 2015. After calculating the evolution of the equation of state as well as the deceleration parameters, we find that with a logarithmic form for the BD scalar field the phantom crossing can be achieved in the late time of cosmic evolution. Unlike the conventional theory of holographic dark energy in standard cosmology ($\omega_D=0$), our model results a late time accelerated expansion. It is also shown that the cosmic coincidence problem may be resolved in the proposed model. We execute the statefinder and Om diagnostic tools and demonstrate that interaction term does not play a significant role. Based on the observational data sets used in this paper it seems that the best value with $1\sigma$ and $2\sigma$ confidence interval are $\Omega_m=0.268^{+0.008~+0.010}_{-0.007~-0.009}$, $ \alpha=3.361^{+0.332~+0.483}_{-0.401~-0.522}$, $\beta=5.560^{+0.541~+0.780}_{-0.510~-0.729}$, $c=0.777^{+0.023~+0.029}_{-0.017~-0.023}$ and $b^2 =0.045$, according to which we find that the proposed model in the presence of interaction is compatible with the recent observational data.

New agegraphic dark energy model in Brans-Dicke theory with logarithmic form of scalar field

In a very recent paper, the current authors (arXiv:gr-qc/1609.01477) have proposed and analyzed in detail the logarithmic form of Brans-Dicke scalar field $\phi$ as $\phi \propto ln(\alpha+\beta a)$, where $\alpha$ and $\beta$ are positive constants, to alleviate the problems of interacting holographic dark energy models in Brans-Dicke theory. In this paper, the cosmological evolution of a new agegraphic dark energy (NADE) model within the framework of Friedmann-Robertson-Walker Universe is analyzed with the same form of scalar field in Brans-Dicke theory. We derive the equation of state parameter $w_D$ and deceleration parameter $q$ of NADE model. It is observed that $w_D\rightarrow -1$ when $a\rightarrow \infty$, i.e., the NADE mimics cosmological constant in the late time evolution. Indeed, due to the assumption of logarithmic form of Brans-Dicke scalar field the NADE in Brans-Dicke theory behaves like NADE in general relativity in the late time evolution. The NADE model shows a phase transition from matter dominated phase in early time to accelerated phase in late time. We further extend NADE model by including the interaction between dark matter and NADE. In this case, $w_D$ definitely crosses the phantom divide line ($w_D=-1$) in the late time evolution. The phase transition from matter dominated to NADE dominated phase may be achieved at early stage in interacting model. Further, we show that the interacting NADE model resolves the cosmic coincidence problem as the energy density ratio may evolve sufficiently slow at present.

Bulk Viscous Cosmological Model in Brans-Dicke Theory with New Form of Time Varying Deceleration Parameter

We have presented FRW cosmological model in the framework of Brans-Dicke theory. This paper deals with a new proposed form of deceleration parameter and cosmological constant Λ. The effect of bulk viscosity is also studied in the presence of modified Chaplygin gas equation of state (p=Aρ-B/ρn). Furthermore, we have discussed the physical behaviours of the models.

Two Fluid Scenario for Axially Symmetric Dark Energy Cosmological Models in Brans-Dicke Theory of Gravitation

Two Fluid Scenario for Axially Symmetric Dark Energy Cosmological Models in Brans-Dicke Theory of Gravitation

FRW cosmological models in Brans-Dicke theory of gravity with variable q $q$ and dynamical Λ $\varLambda$ -term

Exact solution of modified Einstein’s field equations are considered within the scope of spatially homogeneous and isotropic Fraidmann-Robertson-Walker (FRW) space-time filled with perfect fluid in the frame work of Brans-Dicke scalar-tensor theory of gravity. In this paper we have investigated the flat, open and closed FRW models and the effect of dynamic cosmological term on the evolution of the universe. Two types of FRW cosmological models are obtained by setting the power law between the scalar field $\phi$ and the scale factor $a$ and deceleration parameter (DP) $q$ as a time dependent. The concept of time dependent DP with some proper assumptions yield two type of the average scale factors (i) $a(t)=[\sinh(\alpha t)]^{\frac{1}{n}}$ and (ii) $a(t)=[t^{\alpha}e^{t}]^{\frac{1}{n}}$ , $\alpha$ and $n\neq 0$ are arbitrary constants. In case (i), for $0 < n \leq 1$ , it generates a class of accelerating models while for $n > 1$ , the models of the universe exhibit phase transition from early decelerating to present accelerating phase and the transition redshift $z_{t}$ has been calculated and found to be in good agreement with the results from recent astrophysical observations. In case (ii), for $n \geq 2$ and $\alpha = 1$ , we obtain a class of transit models of the universe from early decelerating to present accelerating phase. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time. The physical and geometric properties of the models are also discussed with the help of graphical presentations.

Five dimensional spherically symmetric cosmological model in Brans-Dicke theory of gravitation

In this paper, we consider the spherically symmetric space-time in five dimensions in Brans-Dicke (Phys. Rev. 124:925, 1961) theory of gravitation in the presence of perfect fluid distribution. A determinate solution of the highly non-linear field equations is presented using (i) relation between metric potentials and (ii) an equation of state which represents disordered radiation in five dimensional universe. The solution obtained describes five dimensional radiating model in Brans-Dicke theory. Some physical and kinematical properties of the model are also discussed.

Minimally interacting holographic Dark energy model in Brans-Dicke theory

In this paper, we have studied the anisotropic and homogeneous Bianchi type-V universe filled with two minimally interacting fields, matter and holographic dark energy components in the frame work of Brans and Dicke (Phys. Rev. 124:925, 1961) theory of gravitation. To obtain a determinate solution of the field equations we have used (i) the scalar expansion is proportional to the shear scalar and (ii) special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:182, 1983). Some physical and kinematical properties of the model are also discussed.

Five dimensional radiating model in Brans-Dicke theory of gravitation

A five dimensional Kaluza-Klein space-time is considered in the presence of perfect fluid source in a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). A cosmological model with a negative constant deceleration parameter is presented using a relation between the metric potentials and an equation of state. The model obtained can be considered as a five dimensional radiating universe in this theory. Some physical and kinematical properties of the model are also discussed.

Two fluid scenario for dark energy model in Brans-Dicke theory of gravitation

In this paper, we study the evolution of the dark energy parameter in the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy in the scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 24:925, 1961). A determinate solution is presented using (i) the special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:183, 1983) and (ii) trace free energy momentum tensor of the two fluid. Two cases of interacting and non-interacting fluid (barotropic and dark energy) scenario is considered and general results are obtained. The physical aspects of the results obtained are, also, discussed.

Bianchi type-II, VIII &amp; IX perfect fluid magnetized cosmological models in Brans-Dicke theory of gravitation

Spatially homogeneous Bianchi type-II, VIII & IX charged perfect fluid cosmological models in Brans-Dicke theory of gravitation are obtained and presented. Various physical and geometrical features of the models are also discussed.

Axially symmetric string cosmological models in Brans-Dicke theory of gravitation

Axially symmetric string cosmological models are obtained in a scalar- tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). Some physical and geometrical properties of the models are also discussed. The models are anisotropic and free from singularities.

Five dimensional Bianchi type-I string cosmological model in Brans-Dicke theory

A Bianchi type-I string cosmological model in Brans-Dicke theory in five dimension space-time has been investigated. For the determinate solution it has been assumed that the sum of energy density and tension density of the cosmic string dust source vanishes. Some physical and kinematical parameters are also discussed.

Axially Symmetric String Cosmological Model In Brans-Dicke Theory of Gravitation

By adopting the co-moving coordinate system, an exact axially symmetric cosmological model with string dust cloud source is obtained in the framework of Brans-Dicke [Phys. Rev. 124, 925, (1961) Scalar – tensor theory of gravitation. Some physical and kinematical properties of the model are also discussed.