A higher-dimensional string cosmological model in Brans–Dicke theory of gravitation

Field equations in the presence of cosmic string source are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124, 925 (1961)) with the aid of a five-dimensional Kaluza–Klein metric. An exact string cosmological model is presented which represents a five-dimensional Reddy string (Astrophys. Space Sci. 286, 2003b) in Brans–Dicke theory. Some physical properties of the model are also discussed     

Bianchi type-III cosmological model in four- and five-dimensional bimetric theory of relativity

Four- and five-dimensional Bianchi type-III cosmological model in Rosen (1980) bimetric theory of gravitation is considered. Restricting to a particular type of background metric, it is observed that the Bianchi type-III cosmological model does not exist in case of both meson field and mesonic perfect fluid. Hence only vacuum model can be obtained.     

The linear problem for the five-dimensional projective field theory

A linear problem is given for the five-dimensional projective theory when the metric depends only on two coordinates. The symmetries of this problem are investigated.     

Particle motion in the field of a five-dimensional charged black hole

In this paper, we have investigated the geodesics of neutral particles near a five-dimensional charged black hole using a comparative approach. The effective potential method is used to determine the location of the horizons and to study radial and circular trajectories. This also helps us to analyze the stability of radial and circular orbits. The radius of the innermost stable circular orbits have also been determined. Contrary to the case of massive particles for which, the circular orbits may have up to eight possible values of specific radius, we find that the photons will only have two distinct values for the specific radii of circular trajectories. Finally we have used the dynamical systems analysis to determine the critical points and the nature of the trajectories for the timelike and null geodesics.     

A special-relativistic approach to gravitation and its astrophysical consequences

In the framework of Rastall's conservative program for the construction of gravitation theory we present a variant of modified classical gravitation theory based on Einstein's energy-mass equivalence principle. We pursue further the special-relativistic arguments and obtain a theory for the static spherically-symmetric gravitation field that is based only on the well-established physical principles and accounts for all experimental tests known in gravitation. Some astrophysical consequences of the modified classical gravitation theory (e.g., the non-existence of black holes, the creation of real particles in a strong gravitation field) are also discussed.     

The gravitation theory in bimetric formulation

The gravitation theory is considered in bimetric formulation with a Lagrangian of the most common type and quadratic with respect to the derivativesg _ik/l of the metric tensor. Restrictions on the dimensionless parameters of the theory are found, basing on the comparison with the Newtonian theory and the analysis of corresponding observational data in the vicinity of the solar system. Propagation of the weak gravitation waves is investigated in the outside gravitational field.     

Galactic rotation curves and brane-world models

In the present investigation, flat rotational curves of the galaxies are considered under the framework of brane-world models where the four-dimensional effective Einstein equation has extra terms which arise from the embedding of the 3-brane in the five-dimensional bulk. It has been shown here that these long-range bulk gravitational degrees of freedom can act as a mechanism to yield the observed galactic rotation curves without the need for dark matter. The present model has the advantage that the observed rotation curves result solely from well-established non-local effects of gravitation, such as dark radiation and dark pressure under a direct use of the condition of flat rotation curves and does not invoke any exotic matter field.     

Higher-dimensional vacuum Friedmann models in Dunn's theory of gravitation

The vacuum Friedmann-Robertson-Walker (FRW) models are investigated in Dunn's theory of gravitation with extra dimensions and some properties of the solutions are discussed.     

Friedmann cosmological models with bulk viscosity in a scale covariant theory

In the presence of perfect fluid with bulk viscosity homogeneous isotropic Friedmann Cosmologies are studied in the scale covariant theory of gravitation. Using special law of variation for Hubble’s parameter, a class of solutions is found. The physical properties of the model are also investigated.     

Variant of the Bimetric Theory of Gravitation. III. Gravitational Radiation

Gravitational radiation in a variant of the bimetric theory of gravitation is investigated in the case of slow motions and weak fields. Questions of the propagation velocity, polarization, and generation of a weak gravitational wave are considered. The Peters-Matthews coefficients and the dipole emission coefficient are determined.     

Post-Newtonian approximation of gravitation theory in flat space-time

The post-Newtonian approximation of the gravitational field of a perfect fluid for a previously stated theory of gravitation in flat space-time is studied. The conservation laws of energy-momentum and angular-momentum are derived and the equivalence of the conservation law of energy-momentum and the equations of motion is shown to the studied accuracy. The equations of motion are stated. All the results of the post-Newtonian approximation of the gravitation theory in flat space-time and of the general theory of relativity, as considered by Will in his famous book, agree to the studied accuracy.     

Post-newtonian gravitational radiation from binary systems in flat space-time theory of gravitation

For a previously studied theory of gravitation in flat space-time a general formula of the gravitational radiation at large distances from a system of bodies is derived. The calculations are carried out through post-Newtonian order within this theory of gravitation. A more explicit formula is given for a binary system. It agrees with the result of general relativity.     

Inertia and a fifth dimension—special relativity from a new perspective

The phenomenon of inertia is modeled by a new process, which semi-discretely changes the metrical scale of spacetime. This process explains inertia as a curved spacetime phenomenon, since all accelerating trajectories take place on geodesics of general relativity. By this approach inertial reference frames are Minkowskian manifolds imbedded in a five-dimensional space. It would imply a revised interpretation of special relativity, which preserves a universal temporal reference. If acceleration curves spacetime, it would also imply the existence of an energy-momentum tensor with net energy, which under certain conditions could become negative.     

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. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plane-symmetric vacuum in self-creation cosmology

Vacuum field equations for the static and non-static plane-symmetric metric are obtained in self-creation theory of gravitation proposed by Barber (1982). It is shown that, in both static and non-static cases, the only plane-symmetric solution in vacuum is the empty flat space-time of Einstein's theory. It is observed that this result is quite different from that of the Brans-Dicke and other scalar-tensor theories of gravitation.     

Dilaton Stabilization in String Cosmology. III. Models with Curved Space

Within the framework of the mechanism of dilaton stabilization proposed in Part I of the present work, an analysis of homogeneous and isotropic cosmological models of low-energy string gravitation with loop corrections is continued. The behavior of models with curved space is investigated by methods of the qualitative theory of dynamical systems for different values of the singularity index of the dilaton kinetic function and the barotropic index of nongravitational matter. The conditions under which dilaton stabilization occurs as a result of cosmological expansion are determined, and the corresponding phase diagrams are constructed.     

The Ω-field theory of gravitation and cosmology

The present paper presents, within the Einstein conceptual framework, a scalar field theory of gravitation. The -field, however, is not superimposed on the space-time manifold from outside the given geometry but is derived from the space-time torsion which is shown to be the generator of gravitation and inertia as well as spin. The theory predicts the three crucial tests of gravitation to the same degree of accuracy as does Einstein's theory. But it also predicts gravitational radiation emitted by a pulsating sphere and a singularity free cosmology in contradiction to Einstein's results. Above all, the scalar gravitational field can be easily quantized in the present context.     

Qualitative analysis of string cosmology with loop corrections. I

Homogeneous and Isotropic cosmological models of low-energy, string gravitation with loop corrections to the dilaton coupling functions are investigated by methods of the qualitative theory of dynamical systems. An ideal fluid with a barotropic equation of state is considered as the nongravitational source. In the general case of curved models, the cosmological equations are represented in the form of a third-order, autonomous, dynamical system. Phase portraits for different coupling functions are constructed for flat models. The asymptotic behavior of the general solution in limiting regions is investigated. The stabilization of the dilaton is analyzed using the Damour-Polyakov mechanism. Translated from Astrofizika, Vol. 42, No. 1, pp. 117–136, January–March, 1999.     

Number of information and its relation to the cosmological constant resulting from Landauer’s principle

In this study, we have investigated the geometrical and physical properties of stationary axisymmetric solutions. The expressions for the axial-vector and the gravitational energy and momentum densities are obtained in the context of teleparallel equivalent of general relativity. The obtained results are compared with that obtained previously in the context of Møller’s tetrad theory of gravitation. We discussed special cases of these solutions.     

Vacuum Friedmann models in self-creation cosmology

The vacuum Friedmann models are investigated in self-creation theory of gravitation proposed by Barber. New solutions are obtained forK=±1, and some properties of the solutions are discussed. Only theK=0 solution in self-creation cosmology was previously shown.