Cosmological Model with Cosmic Transit Behavior in Brans-Dicke Theory

Anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans-Dicke theory with a self interacting potential. Wet dark fluid characterized by a linear equation of state is considered as the source of dark energy. Shear scalar is considered to be proportional to the expansion scalar simulating an anisotropic relationship among the directional expansion rates. The dynamics of the universe in presence of wet dark fluid in anisotropic background have been discussed. The presence of evolving scalar field makes it possible to get accelerating phase of expansion even for a linear relationship among the directional Hubble rates. It is found that, the anisotropy in expansion rates does not affect the scalar field, self interacting potential but it controls the non-evolving part of the Brans- Dicke parameter.

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.

Unified dark fluid and cosmic transit models in Brans–Dicke theory

In this study, we search for a new class of wormhole solutions in the framework of Brans–Dicke (BD) theory in the presence of anisotropic matter distribution. Considering a linear equation of state (EoS) between radial pressure and energy density profile we find exact static spherically symmetric solutions to the BD field equations which represent wormhole configurations. The solutions we obtain include both cases with zero and nonzero redshift functions, for which, the conditions on wormhole geometry together with the weak (WEC) and null (NEC) energy conditions put constraints on model parameters such as, the BD coupling and EoS parameters. These constraints also depend on other model parameters such as, the value of BD scalar field and energy density at the wormhole throat. The regularity of the obtained solutions is verified by calculating the Kretschmann scalar in order to ensure that curvature singularities are absent in the wormhole spacetime. We then find that BD wormholes in the presence of anisotropic matter can exist without violating NEC and WEC, either at the throat or across the entire spacetime.

Recently, it has been shown that a four-dimensional (4D) Brans–Dicke (BD) theory with an effective matter field and a self-interacting potential can be achieved from the vacuum 5D BD field equations, where we refer to as a modified Brans–Dicke theory (MBDT). We investigate a generalized Bianchi type I anisotropic cosmology in 5D BD theory, and by employing the obtained formalism, we derive the induced matter on any 4D hypersurface in the context of the MBDT. We illustrate that if the usual spatial scale factors are functions of the time while the scale factor of extra dimension is constant, and the scalar field depends on the time and the fifth coordinate, then, in general, one will encounter inconsistencies in the field equations. Then, we assume that the scale factors and the scalar field depend on the time and the extra coordinate as separated variables in the power-law forms. Hence, we find a few classes of solutions in 5D spacetime through which we probe the one which leads to a generalized Kasner relation among the Kasner parameters. The induced scalar potential is found to be in the power law or in the logarithmic form; however, for a constant scalar field and even when the scalar field only depends on the fifth coordinate, it vanishes. The conservation law is indeed valid in this MBDT approach for the derived induced energy–momentum tensor (EMT). We proceed our investigations for a few cosmological quantities, where for simplicity we assume that the metric and the scalar field are functions of the time. Hence, the EMT satisfies the barotropic equation of state, and the model indicates that the constant mean Hubble parameter is not allowed. Thus, by appealing to the variation of the Hubble parameter, we assume a fixed deceleration parameter, and set the evolution of the quantities with respect to the fixed deceleration, the BD coupling and the state parameters. The WEC allows a shrinking extra dimension for a decelerating expanding universe that, in the constant scalar field, evolves the same way as the flat FRW spacetime in GR. The quantities for the stiff fluid and the radiation-dominated universe indicate an expanding universe commenced with a big bang. There is a horizon for each of the fluids, and the rate of expansion slows down by the time. The allowed ranges of the deceleration and the BD coupling parameters have been obtained, and the model gives an empty universe when the time goes to infinity.

In this paper, we solve Brans–Dicke (BD) theory (Phys. Rev. D, 24, 925) field equations for anisotropic Bianchi type VI0 space–time and discuss evolution of the expanding Universe. Here, we consider pressureless fluid and isotropic generalized ghost pilgrim dark energy as the source of matter and dark energy, respectively. To get the determinate solution of the field equations we have used (i) scalar expansion proportional to the shear scalar and (ii) scalar field (in BD theory) proportional to average scale factor of the model. Some physical and geometrical properties of the model are also discussed.

We show that Friedmann-Robertson-Walker (FRW) geometry with flat spatial section in quantized (Wheeler deWitt quantization) Brans Dicke (BD) theory reveals a rich phase structure owing to anomalous breaking of a classical symmetry, which maps the scale factor $a\mapsto\lambda a$ for some constant $\lambda$. In the weak coupling ($\omega$) limit, the theory goes from a symmetry preserving phase to a broken phase. The existence of phase boundary is an obstruction to another classical symmetry [arXiv:gr-qc/9902083] (which relates two BD theory with different coupling) admitted by BD theory with scale invariant matter content i.e $T^{\mu}{}_{\mu}=0$. Classically, this prohibits the BD theory to reduce to General Relativity (GR) for scale invariant matter content. We show that strong coupling limit of BD and GR both preserves the symmetry involving scale factor. We also show that with a scale invariant matter content (radiation i.e $P=\frac{1}{3}\rho$), the quantized BD theory does reduce to GR as $\omega\rightarrow\infty$, which is in sharp contrast to classical behavior. This is a first known illustration of a scenario, where quantized BD theory provides example of anomalous symmetry breaking and resulting binary phase structure. We make a conjecture regarding strong coupling limit of BD theory in generic scenario.

Rip behaviour in Brans–Dicke theory

In this paper, we have generalized the behaviors of transit cosmological model under the observational data with Barrow holographic dark energy. We consider the scale factor field as [Formula: see text] to get exact solutions for the field equations in a non-flat FRW universe in Brans–Dicke theory. The values of the model parameters [Formula: see text] and [Formula: see text] are obtained by best fitting of 46 observational Hubble data (OHD) points in the range [Formula: see text]. The derived model exhibits a transition scenario for open, flat and closed universe. The EoS parameter shows a quintom-like behavior, lies both quintessence ([Formula: see text]) and phantom ([Formula: see text]) regions and crosses the phantom divide. The matter and dark energy density parameters [Formula: see text], scalar field [Formula: see text] and other cosmological parameters provide the results consistent with the recent observational datasets. Some other physical and geometrical behaviors of BHDE are also described and the satisfactory behaviors are found with current observations (OHD+JLA).

Dark energy with the usually used equation of state p = wρ, where w = const < 0, is hydrodynamically unstable. To overcome this drawback, we consider the cosmology of a perfect fluid with a linear equation of state of a more general form p = α(ρ − ρ0), where the constants α and ρ0 are free parameters. This non-homogeneous linear equation of state provides the description of both hydrodynamically stable (α > 0) and unstable (α < 0) fluids. In particular, the considered cosmological model describes the hydrodynamically stable dark (and phantom) energy. The possible types of cosmological scenarios in this model are determined and classified in terms of attractors and unstable points by using phase trajectories analysis. For the dark energy case, some distinctive types of cosmological scenarios are possible: (i) the universe with the de Sitter attractor at late times, (ii) the bouncing universe, (iii) the universe with the big rip and with the anti-big rip. In the framework of a linear equation of state the universe filled with a phantom energy, w < −1, may have either the de Sitter attractor or the big rip.

The evolution of universe in Brans-Dicke (BD) theory is discussed in this paper. Considering a parameterized scenario for BD scalar field $\phi=\phi_{0}a^{\alpha}$ which plays the role of gravitational "constant" $G$, we apply the Markov Chain Monte Carlo method to investigate a global constraints on BD theory with a self-interacting potential according to the current observational data: Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. It is shown that an expanded universe from deceleration to acceleration is given in this theory, and the constraint results of dimensionless matter density $\Omega_{0m}$ and parameter $\alpha$ are, $\Omega_{0m}=0.286^{+0.037+0.050}_{-0.039-0.047}$ and $\alpha=0.0046^{+0.0149+0.0171}_{-0.0171-0.0206}$ which is consistent with the result of current experiment exploration, $\mid\alpha\mid \leq 0.132124$. In addition, we use the geometrical diagnostic method, jerk parameter $j$, to distinguish the BD theory and cosmological constant model in Einstein's theory of general relativity.

Geodesic deviation equation in Brans–Dicke theory in arbitrary dimensions

A linear relationship between the Hubble expansion parameter and the time derivative of the scalar field is explored in order to derive exact cosmological, attractor-like solutions, both in Einstein's theory and in Brans–Dicke gravity with two fluids: a background fluid of ordinary matter and a self-interacting scalar-field fluid accounting for the dark energy in the universe. A priori assumptions about the functional form of the self-interaction potential or about the scale factor behaviour are not necessary. These are obtained as outputs of the assumed relationship between the Hubble parameter and the time derivative of the scalar field. A parametric class of scaling quintessence models given by a self-interaction potential of a peculiar form, a combination of exponentials with dependence on the barotropic index of the background fluid, arises. Both normal quintessence described by a self-interacting scalar field minimally coupled to gravity and Brans–Dicke quintessence given by a non-minimally coupled scalar field are then analysed and the relevance of these models for the description of the cosmic evolution is discussed in some detail. The stability of these solutions is also briefly commented on.

This paper is devoted to study Bianchi type I cosmological model in Brans–Dicke theory with self-interacting potential by using perfect, anisotropic and magnetized anisotropic fluids. We assume that the expansion scalar is proportional to the shear scalar and also take a power law ansatz for the scalar field. The physical behavior of the resulting models are discussed through different parameters. We conclude that contrary to the universe model, the anisotropic fluid approaches isotropy at later times in all cases, which is consistent with observational data.

In this paper, we study the behavior of non-interacting and interacting pilgrim dark energy (DE) for non-flat FRW model in Brans–Dicke (BD) theory. We consider the future event horizon as well as logarithmic form of BD scalar field [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] is the scale factor. We evaluate some well-known cosmological parameters such as equation of state as well as deceleration parameter and [Formula: see text] plane as well as statefinder parameters. We discuss graphical behavior of these parameters through pilgrim DE parameter [Formula: see text] for both non-interacting as well as interacting case with interacting parameter [Formula: see text]. It is found that the equation of state parameter gives consistent results with the current cosmic behavior while the deceleration parameter represents transition from decelerated to accelerated phase. The cosmological planes represent different DE regions. Finally, we discuss stability of the model through squared speed of sound in both cases.