Field equations in the neighbourhood of a particle in a conformal theory of gravitation

1968 ◽  
Vol 306 (1487) ◽  
pp. 487-501 ◽  
Keyword(s):  
Boundary Conditions ◽  
Special Solution ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Conformal Theory ◽  
Usual Form ◽  
Theory Of Gravitation ◽  
Spherically Symmetric Metric

The field equations in the neighbourhood of a particle for a spherically symmetric metric in the conformal theory of gravitation put forward by Hoyle & Narlikar are examined in detail. This metric is assumed to be of the usual form d s 2 = e v d t 2 —e λ d r 2 — r 2 (d θ 2 + sin 2 θ d ψ 2 ) where λ and v are functions of r only. Hoyle & Narlikar obtained a solution of the field equations under the assumption λ + v = 0. In this paper the case λ + v ǂ 0 is investigated, and it is shown that the only solution that satisfies all the boundary conditions is the special solution obtained by setting λ + v = 0. The significance of this result is discussed.

Field equations in the neighbourhood of a particle in a conformal theory of gravitation. II

1969 ◽  
Vol 313 (1512) ◽  
pp. 71-82 ◽  
Keyword(s):  
Local Geometry ◽  
Field Equations ◽  
Schwarzschild Solution ◽  
Conformal Theory ◽  
Conformally Invariant ◽  
Coordinate Singularity ◽  
Previous Solution ◽  
Theory Of Gravitation ◽  
Spherically Symmetric Metric ◽  
Radial Variable

The field equations in the neighbourhood of a particle for a spherically symmetric metric in the conformal theory of gravitation put forward by Hoyle & Narlikar are examined. As the theory is conformally invariant, one can use different but physically equivalent conformal frames to study the equations. Previously these equations were studied in a conformal frame which, though suitable far away from the isolated particle, turns out not to be suitable in the neighbourhood of the particle. In the present paper a solution in a conformal frame is obtained that is suitable for considering regions near the particle. The solution thus obtained differs from the previous one in several respects. For example, it has no coordinate singularity for any non-zero value of the radial variable, unlike the previous solution or the Schwarzschild solution. It is also shown with the use of this solution that in this theory distant matter has an effect on local geometry.

On a conformal theory of gravitation

1967 ◽  
Vol 63 (3) ◽  
pp. 809-817 ◽  
Author(s):  
Jamal N. Islam
Keyword(s):  
Explicit Solution ◽  
Special Form ◽  
Gravitational Constant ◽  
Special Solution ◽  
Field Equations ◽  
Conformal Theory ◽  
Theory Of Gravitation

AbstractRecently Hoyle and Narlikar(2) have put forward a conformal theory of gravitation in which they obtain an explicit solution of the field equations using certain approximations and assumptions of symmetry. To obtain the solution, the metric is assumed to have a special form. In the present paper a more general form of the metric is considered, and it is shown that many of the features of the special solution are shared by the solution in the more general case. In particular, the implications of the special solution as concerns the sign of the gravitational constant remain valid in the more general case under certain assumptions.

Equivalence principle for charged bodies in a theory of gravitation

1981 ◽  
Vol 59 (11) ◽  
pp. 1730-1733 ◽  
Author(s):  
R. B. Mann ◽  
J. W. Moffat
Keyword(s):  
Equivalence Principle ◽  
Maxwell Equations ◽  
Test Body ◽  
Spherically Symmetric ◽  
Point Particles ◽  
Symmetric Field ◽  
Static Spherically Symmetric Metric ◽  
Theory Of Gravitation ◽  
Spherically Symmetric Metric

The motion of a test body made of electromagnetically interacting point particles, falling in the static spherically symmetric field of the Hermitian theory of gravitation is shown to not disagree with the Eötvös–Dicke–Braginsky experiments for the equivalence principle. The modified Maxwell equations are calculated in the isotropic static spherically symmetric metric, and the role of the equivalence principle in the new theory is discussed in detail.

scholarly journals Dark Energy as a Cosmological Consequence of Existence of the Dirac Scalar Field in Nature

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
O. V. Babourova ◽  
B. N. Frolov
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Early Universe ◽  
Large Time ◽  
Field Equations ◽  
Conformal Theory ◽  
Effective Cosmological Constant ◽  
Theory Of Gravitation ◽  
Cosmological Consequence

The solution of the field equations of the conformal theory of gravitation with Dirac scalar field in Cartan-Weyl spacetime at the very early Universe is obtained. In this theory dark energy (described by an effective cosmological constant) is a function of the Dirac scalar field β. This solution describes the exponential decreasing of β at the inflation stage and has a limit to a constant value of the dark energy at large time. This can give a way to solving the fundamental cosmological constant problem as a consequence of the fields dynamics in the early Universe.

scholarly journals Metric-Affine Geometries with Spherical Symmetry

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 453 ◽  
Author(s):  
Manuel Hohmann
Keyword(s):  
Spherical Symmetry ◽  
Rotation Group ◽  
Spin Connection ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Comprehensive Overview ◽  
Pure Rotation ◽  
Affine Geometries ◽  
Spherically Symmetric Metric

We provide a comprehensive overview of metric-affine geometries with spherical symmetry, which may be used in order to solve the field equations for generic gravity theories which employ these geometries as their field variables. We discuss the most general class of such geometries, which we display both in the metric-Palatini formulation and in the tetrad/spin connection formulation, and show its characteristic properties: torsion, curvature and nonmetricity. We then use these properties to derive a classification of all possible subclasses of spherically symmetric metric-affine geometries, depending on which of the aforementioned quantities are vanishing or non-vanishing. We discuss both the cases of the pure rotation group SO ( 3 ) , which has been previously studied in the literature, and extend these previous results to the full orthogonal group O ( 3 ) , which also includes reflections. As an example for a potential physical application of the results we present here, we study circular orbits arising from autoparallel motion. Finally, we mention how these results can be extended to cosmological symmetry.

Experimental tests of a new theory of gravitation

1981 ◽  
Vol 59 (2) ◽  
pp. 283-288 ◽  
Author(s):  
J. W. Moffat
Keyword(s):  
Upper Bound ◽  
Symmetric Solution ◽  
Satellite Orbit ◽  
Experimental Tests ◽  
Spherically Symmetric ◽  
The Sun ◽  
Field Equations ◽  
Spherically Symmetric Solution ◽  
Perihelion Shift ◽  
Theory Of Gravitation

The predictions for the perihelion shift, the deflection of light, and the delay time of a light ray are calculated in the nonsymmetric theory of gravitation. An upper bound for the parameter l (that occurs as a constant of integration in the static, spherically symmetric solution of the field equations) is obtained for the sun for the experimental value of the perihelion shift of Mercury, yielding [Formula: see text]. The upper bound on [Formula: see text] obtained from the Viking spacecraft time-delay experiment is [Formula: see text]. For [Formula: see text], we find that the theory is consistent with the standard relativistic experiments for the solar system. The theory predicts that the perihelion of a satellite could reverse its direction of precession if it orbits close enough to the sun. The results for a highly eccentric satellite orbit are calculated in terms of the value [Formula: see text].

Static spherically symmetric solutions in f(G) gravity

2016 ◽  
Vol 25 (07) ◽  
pp. 1650083 ◽  
Author(s):  
M. Sharif ◽  
H. Ismat Fatima
Keyword(s):  
Equation Of State ◽  
State Parameter ◽  
Energy Conditions ◽  
Conformal Killing ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Anisotropic Matter ◽  
Physical Validity ◽  
Spherically Symmetric Metric ◽  
Anisotropic Case

We investigate interior solutions for static spherically symmetric metric in the background of [Formula: see text] gravity. We use the technique of conformal Killing motions to solve the field equations with both isotropic and anisotropic matter distributions. These solutions are then used to obtain density, radial and tangential pressures for power-law [Formula: see text] model. For anisotropic case, we assume a linear equation-of-state and investigate solutions for the equation-of-state parameter [Formula: see text]. We check physical validity of the solutions through energy conditions and also examine its stability. Finally, we study equilibrium configuration using Tolman–Oppenheimer–Volkoff equation.

scholarly journals CHARGED POLYTROPIC STARS AND A GENERALIZATION OF LANE–EMDEN EQUATION

2004 ◽  
Vol 13 (07) ◽  
pp. 1441-1445 ◽  
Author(s):  
RODRIGO PICANÇO ◽  
MANOEL MALHEIRO ◽  
SUBHARTHI RAY
Keyword(s):  
Equation Of State ◽  
Differential Equations ◽  
Electric Field ◽  
Boundary Conditions ◽  
Radial Component ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Emden Equation ◽  
Polytropic Equation ◽  
Structure Equations

In this paper we discuss charged stars with polytropic equation of state, where we derive an equation analogous to the Lane–Endem equation. We assume that these stars are spherically symmetric, and the electric field have only the radial component. First we review the field equations for such stars and then we proceed with the analog of the Lane–Emden equation for a polytropic Newtonian fluid and their relativistic equivalent (Tooper, 1964).1 These kind of equations are very interesting because they transform all the structure equations of the stars in a group of differential equations which are much more simple to solve than the source equations. These equations can be solved numerically for some boundary conditions and for some initial parameters. For this we assume that the pressure caused by the electric field obeys a polytropic equation of state too.

Charged perfect fluid gravitational collapse in f(R, T) gravity

2019 ◽  
Vol 34 (20) ◽  
pp. 1950153 ◽  
Author(s):  
G. Abbas ◽  
Riaz Ahmed
Keyword(s):  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Coupling Parameter ◽  
Apparent Horizon ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Apparent Horizons ◽  
Spherically Symmetric Metric

We explore the problem of charged perfect fluid spherically symmetric gravitational collapse in f(R, T) gravity (R is Ricci scalar and T is the trace of energy–momentum tensor). We have taken the interior boundary of a star as spherically symmetric metric filled with the charged perfect fluid. In order to study charged perfect fluid collapse, we have investigated the exact solutions of the Maxwell–Einstein field equations solutions using the most simplified form for f(R, T) model f(R, T) = R + 2[Formula: see text]T, where [Formula: see text] is model parameter. This study involves the effects of charge as well as coupling parameter on collapse of a star. We studied the nature of trapped surfaces, apparent horizon and singularity structure in detail. It has been found that singularity is formed earlier than the apparent horizons, so the end state of gravitational collapse in this case is black hole.

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