Brans-Dicke Theory Of Gravitation Research Articles

Bianchi Types II, VIII and IX String Cosmological Models with Bulk Viscosity in Brans-Dicke Theory of Gravitation

We have obtained and presented spatially homogeneous Bianchi types II, VIII and IX string cosmological models with bulk viscosity in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). It is observed that in case of Bianchi type-IX universe, only bulk viscous cosmological model exists. Some physical and geometrical properties of the models are also discussed.

Bianchi type-II, VIII & 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.

Mach’s principle

The underlying idea in Mach’s principle is that the origin of inertia or mass of a particle is a dynamical quantity determined by the environment, in particular the rest of the matter in the universe. In this article, we discuss the role of this idea in the Brans-Dicke theory of gravitation and the Hoyle-Narlikar cosmology.

DILATON COSMOLOGY

In Brans–Dicke gravitational theory, an analytical accelerating expansion solution of the Universe is found at the dilaton dominated epoch. Both Einstein frame (EF) and Jordan frame (JF) are applied. We consider the form of exponential potential of dilaton field in EF while we consider the power law potential in JF. In matter and dilaton coexisting epoch, only the decelerating expansion solution without potential is considered with experimental constraint α2<0.001. If the power law potential of dilaton field is applied in JF, some authors found the dilaton field can act as quintessence based numerical method.1 We find that the influence of dilaton will not change the evolutionary law of density perturbation of baryon matter.

Fermions in Brans-Dicke cosmology

Using the Brans-Dicke theory of gravitation we put under investigation a hypothetical universe filled with a fermionic field (with a self interaction potential) and a matter constituent ruled by a barotropic equation of state. It is shown that the fermionic field (in combination with the Brans-Dicke scalar field) could be responsible for a final accelerated era, after an initial matter dominated period.

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.

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.

Q-stars in scalar–tensor gravitational theories

We study q-stars in Brans–Dicke gravitational theory. We find that when the Brans–Dicke constant, ωBD, tends to infinity, the results of general relativity are reproduced. For other values of ωBD, the particle number, mass and radius of the star and the absolute value of the matter field are a few percent larger than in the case of general relativity. We also investigate the general scalar–tensor gravitational theory and find that the star parameters are a few percent larger than in the case of general relativity.

A String cosmological model in Brans-Dicke theory of gravitation

A spatially homogeneous and anisotropic exact Bianchi type-I string cosmological model is investigated in Brans-Dicke (1961) scalar-tensor theory of gravitation. Some properties of the model are also discussed.

ON THE COSMOLOGICAL CONSTANT IN QUANTUM COSMOLOGY OF THE BRANS–DICKE THEORY

We study the issue of the cosmological constant in quantum cosmology combined with the Brans–Dicke gravitational theory. Using the minisuperspace approximation, we build up the Wheeler–De Witt equation and then obtain the wave function of the universe by further assuming the WKB approximation under the boundary condition proposed by Vilenkin. It is shown that the amplitude of the resulting wave function, which represents an expanding universe, reaches its peaks if the cosmological constant vanishes.

Critical Behavior in the Brans-Dicke Theory of Gravitation

The collapse of a massless scalar field in the Brans-Dicke theory of gravitation is studied in the analysis of both analytical solution and numerical one. By conformally transforming the Roberts's solution into the Brans-Dicke frame, we find for $\omega > -3/2$ that a continuous self-similarity continues and that the critical exponent does depend on $\omega$. By conformally transforming the Choptuik's solution into the Brans-Dicke frame, we find for $\omega > -3/2$ that at the critical solution shows discrete self-similarity, however, the critical exponent depends strongly on $\omega$ while the echoing parameter weakly on it.

Collapse to black holes in Brans-Dicke theory. I. Horizon boundary conditions for dynamical spacetimes.

We present a new numerical code that evolves a spherically symmetric configuration of collisionless matter in the Brans-Dicke theory of gravitation. In this theory the spacetime is dynamical even in spherical symmetry, where it can contain gravitational radiation. Our code is capable of accurately tracking collapse to a black hole in a dynamical spacetime arbitrarily far into the future, without encountering either coordinate pathologies or spacetime singularities. This is accomplished by truncating the spacetime at a spherical surface inside the apparent horizon, and subsequently solving the evolution and constraint equations only in the exterior region. We use our code to address a number of long-standing theoretical questions about collapse to black holes in Brans-Dicke theory.

Collapse to black holes in Brans-Dicke theory. II. Comparison with general relativity

We discuss a number of long-standing theoretical questions about collapse to black holes in the Brans-Dicke theory of gravitation. Using a new numerical code, we show that Oppenheimer-Snyder collapse in this theory produces black holes that are identical to those of general relativity in final equilibrium, but are quite different from those of general relativity during dynamical evolution. We find that there are epochs during which the apparent horizon of such a black hole passes {\it outside\/} the event horizon, and that the surface area of the event horizon {\it decreases\/} with time. This behavior is possible because theorems which prove otherwise assume $R_{ab}l^al^b \ge 0$ for all null vectors $l^a$. We show that dynamical spacetimes in Brans-Dicke theory can violate this inequality, even in vacuum, for any value of $\omega$.

Wormholes in the Brans-Dicke theory of gravitation.

It is shown that the static spherically symmetric solutions to the Brans-Dicke theory of gravitation give rise either to a naked singularity if the post Newtonian parameter \ensuremath{\gamma}1 or to a wormhole if \ensuremath{\gamma}>1.

Exact solutions in Brans-Dicke theory with bulk viscosity

The effect of bulk viscosity on the evolution of the homogeneous and isotropic cosmological models in the Brans-Dicke theory of gravitation is studied. Solutions are found, with a baratropic equation of state, a time-independent bulk viscosity, the gravitational “constant” inversely proportional to the age of the universe, and the mass of the universe (in the closed model) proportional to the square of its age; the expansion factor is a linear function of the cosmological time. For flat space, power law expansions are found, among them one that is related to extended inflation.

Evidence of chaotic behaviour in Jordan-Brans-Dicke cosmology

We study numerically the properties of solutions of spatially homogeneous Bianchi-type IX cosmological models in the Jordan- Brans-Dicke theory of gravitation. Solutions are obtained in which the scale factors undergo irregular oscillations. The estimate of the maximum Lyapunov exponent is found to be positive in the cases studied. These results seem to be the first pieces of evidence in the literature of chaotic behaviour in Jordan-Brans-Dicke cosmology. The range of values of the Jordan-Brans- Dicke coupling parameter considered is (-500,-1).

Lie group for the Jordan and Brans-Dicke cosmology

A method based on the invariace under a continuous Lie group of transformations is worked out to reduce the problem of finding solutions to the cosmological equations of Jordan and Brans-Dicke theory of gravitation for the Robertson-Walker metrics and the cases of the dust universe and the vacuum universe. The reduction consists in a first-order differential equation and a quadrature for each case. Previously known cosmological solutions are re-obtained. In particular, it becomes apparent during the development of this scheme that the flat-space solutions are indeed the general solution.

The quantum cosmology in the Brans-Dicke theory

In this paper, we try to establish the quantum cosmology based on the Brans-Dicke gravitational theory. The most remarkable property of it is that the scale factora(t) has a lower limit, where the cosmological wave function approaches zero.

Electromagnetic Brans-Dicke-Bianchi type-V solutions

We derive new solutions for the locally rotational-symmetric Bianchi type-V space-time in the Brans-Dicke theory of gravitation. The solutions represent anisotropic cosmological models filled with ‘stiff’ matter and an electromagnetic null field, including the vacuum case. It is shown that the scalar field ϕ is dynamically an essential factor, since it influences the structure of the singularities and the expansion of the models.

Some special non-flat BDT-FRW solutions with a cosmological constant

We consider the non-flatk2=1 Friedmann-Robertson-Walker models with a non-vanishing cosmological constant in the Brans-Dicke theory of gravitation. Some special solutions are given in case of Ω=0, which may be considered as exact solutions of the projective theory of Jordan and Thiry.