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.     

Is dark matter created in the gravitation field of galaxies?

Using the heuristic arguments of quantum physics we describe a new mechanism of the creation of short-living particles from the virtual ones in a stationary gravitation field. The mass of these particles is a function of the intensity of gravitation field. We suppose that the particles created in the gravitation field form a part of the non-baryonic dark matter. Having the intensity of gravitation field in a galaxy we can calculate the density of dark matter created in it by the vacuum quantum fluctuation. We calculate the distribution of this dark matter in a model galaxy and show that its total mass is comparable with the visible mass of the galaxy.     

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.     

Polteilchen in der TREDERSchen Tetradentheorie

In the framework of TREDERS ' tetrad theory of gravitation the interaction of pole-particles is considered in post-NEWTON ian approximation. The perihelion shift for the two-body problem is calculated for different matter-field-couplings. In general it depends not only from the sum of the masses but also from the reduced mass. The additional term is connected with the absorption of gravitation.     

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.     

Exact Bianchi type II, VIII and IX string cosmological models in General Relativity and self-creation theory of gravitation

Exact Bianchi type II, VIII and IX String cosmological models are obtained in Einstein’s theory of gravitation and Barber’s (1982) second self-creation theory of gravitation. Some physical and geometrical properties of the models are also discussed.     

Die Absorption der Schwerkraft und das SEELIGER-YUKAWA-Potential,Akademiker W. A. AMBARZUMJAN zum 65. Geburtstag zugeeignet

In our tetrad-formulation of the gravitation theory a potential-like interaction between the gravitationpotential and the matter-tensor is postulated. In the case of a dust-like matter from this interaction results a screening of the quasi-NEWTON ian potential by the matter-density given by a SEELIGER -YUKAWA -potential with the absorptionconstant approximately. — In the cosmological case from this screening of gravitation a finite effective gravitationradius R of the universe is resulting which radius R is given by the condition for an EINSTEIN -universe 4.     

On Some Bianchi Type Cosmological Models in a Bimetric Theory of Gravitation

Spatially-homogeneous and anisotropic Bianchi type-III, V, VI₀ cosmological models in Rosen's (1973) bimetric theory of gravitation are considered. It is shown that, in each case, when the soure of the gravitation field is a perfect fluid distribution Bianchi type cosmological models do not exist. Hence vacuum models are presented and studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sun-perturbed earth-to-moon transfers with low energy and moderate flight time

We construct a spacecraft transfer with low cost and moderate flight time from the Earth to the Moon. The motion of the spacecraft is modeled by the planar circular restricted three-body problem including a perturbation due to the solar gravitation. Our approach is to reduce computation of optimal transfers to a non-linear boundary value problem. Using a computer software called AUTO, we solve it and continue its solutions numerically to obtain the optimal transfers. Our result also shows that the use of the solar gravitation can further lower the transfer cost drastically.     

On new limits of the coefficient of gravitation shielding

New limits of the shielding coefficients in the supposed phenomenon of gravitation shielding have recently become available. The new values are briefly reviewed and discussed in order to update the state of art since some new limits for gravitation shielding are not necessarily the lowest ones which, instead, are those of interest when planning new experimental research or studying theoretically the possible effects of gravitation shielding.     

Bianchi type-V anisotropic cosmological models in certain theories of gravitation with perfect fluid distribution

Exact Bianchi type-V cosmological models are presented in Einstein’s theory of gravitation with cosmological constant Λ in case of perfect fluid distribution. Also obtained Bianchi type-V cosmological models in a scalar-tensor theory of gravitation proposed by Saez and Ballester (1986) in case of perfect fluid distribution using and without using negative constant deceleration parameter. Some physical and geometrical properties of the models are also discussed.     

The Post-post-Newtonian Amendments of Radar Echo Delay Test in Reissner-Nordström Field

Starting from the differential equation of motion of photons on equatorial plane and in spherically symmetric field of gravitation and adopting the post-Newtonian approximate method, the post-post-Newtonian amendments of radar echo delay test in the Reissner-Nordström metric field are investigated. Via calculations the post-Newtionian and post-post-Newtonian amendments are obtained. When the electric charge Q is equal to zero, these results are applicable to electrically neutral celestial bodies, and the amendments of post-Newtonian parts are consistent with those provided by classical literature. The approximate expansion used in this paper can also be adopted to probe the amendments of still higher orders. The high-order amendments for radar echo have important significance to the ongoing high-precision spatial gravitation tests.     

Bianchi type-VI0 cosmological model in the general scalar-tensor theory of gravitation

The exact Bianchi type-VI₀ stiff-fluid cosmological model is obtained in the Nordtvedt-Barker general scalar-tensor theory of gravitation. Some properties of the model are discussed.     

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.     

Accretion disks in bimetric theory of gravitation. A strong field test of general relativity?

The sensitivity of accretion disk models with respect to its inner boundary conditions, being located in the strong gravity region of a highly compact central body, is used to discuss a possibility of strong field tests of gravitation via compact source observations. Within the bimetric theory of gravitation the optically thin bremsstrahlung model is calculated as an example for this possibility. Using this model to describe the innermost region of the “bimetric disk”, significant differences with respect to the corresponding results in Einstein's theory were found. The more massiv and compact “bimetric disk” radiates softer with higher luminosity.     

Tidal gravitational redshifts of spectral lines in geometrodynamics

An alternative approach is proposed for the study of the non-cosmological redshifts. The approach is based on the radiation formulation of the tidal gravitation acceleration in geometrodynamics and the spacetime curvature around the massive objects. The resulting formalism can be used to study the object mass and the gravitation magnitude from the observed spectral lines with redshifts.     

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.     

Strong spherical shock wave propagation in a self-gravitating RMHD rotating interplanetary medium

In the present paper, we have discussed the propagation of spherical shock waves in a radiating magnetohydrodynamic rotating interplanetary medium. The effects of force of self-gravitation have been taken into account with the assumption that at the equilibrium position the effects of rotation on the force of gravitation are negligible. The combined effects of rotation and gravitation on the variation of flow variables have been shown in tables. The particular cases of the problem have been discussed and compared by considering effects of rotation and gravitation separately.     

On the gravitomagnetic origins of the anomalous flat rotation curves of spiral galaxies

We demonstrate that in-principle, one of the five solutions presented in the reading Nyambuya (2015b), i.e., a solution of the Four Poisson-Laplace equation of gravitation [or Nordström (1912) equation of gravitation] can be used to explain the anomalous flat rotation curves of spiral galaxies. The proposed solution does not invoke the exotic hypothesis of darkmatter but makes the assumption that our existing Laws of Gravitation need to be amended. Our proposed amendment falls well within the accepted domain of legitimate gravitational field equations.