scholarly journals String Theory Explanation of Galactic Rotation Found Using the Geodesic Constraint

2019 ◽  
Vol 2019 ◽  
pp. 1-4
Author(s):  
Mark D. Roberts
Keyword(s):  
String Theory ◽  
Low Energy ◽  
Galactic Rotation ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
De Sitter ◽  
Energy Limit ◽  
Field Equations ◽  
Tensor Theory ◽  
Spherically Symmetric Metric

The unique spherically symmetric metric which has vanishing Weyl tensor, is asymptotically de-Sitter, and can model constant galactic rotation curves is presented. Two types of field equations are shown to have this metric as an exact solution. The first is Palatini varied scalar-tensor theory. The second is the low energy limit of string theory modified by inclusion of a contrived potential.

Expanding and nonexpanding conformal wormholes, in scalar–tensor theory

2015 ◽  
Vol 24 (08) ◽  
pp. 1550064 ◽  
Author(s):  
Melis Ulu Dogru ◽  
İhsan Yilmaz
Keyword(s):  
Casimir Effect ◽  
Lyra Geometry ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Geometrical Properties ◽  
Big Rip ◽  
Tensor Theory ◽  
Big Crunch

We study spherically symmetric spacetime with anisotropic fluid in the scalar–tensor theory of gravity based on Lyra geometry. We suggest two different solutions of field equations for the theory by using Casimir effect. Obtained static and nonstatic solutions are similar to nonexpanding Lorentzian wormhole and expanding FRW-type wormhole, respectively. Furthermore, we study singularities of obtained solutions. We emphasize whether the expanding and nonexpanding wormholes conform with Big Rip or Big Crunch scenarios. Also, physical and geometrical properties of the solutions have been discussed.

A SCALAR-TENSOR THEORY FOR INDUCED GRAVITY

1987 ◽  
Vol 02 (01) ◽  
pp. 179-194 ◽  
Author(s):  
H. BOUTALEB-J. ◽  
A. L. MARRAKCH
Keyword(s):  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Gravitational Constant ◽  
Low Energy ◽  
Scalar Tensor Theory ◽  
Energy Limit ◽  
Potential Minimum ◽  
Induced Gravity ◽  
Tensor Theory ◽  
The Universe

A scalar-tensor theory for induced gravity is presented. Einstein's gravity appears as the low-energy limit of such a theory. It is shown that the spontaneous symmetry breaking can occur at any epoch of the universe and that this mechanism can also be responsible for breaking the unified gauge group SU(5) into SU (3) × SU (2) × U (1). Also, it is shown that, if the spontaneous symmetry breaking is accomplished by means of the Coleman-Weinberg potential minimum, the induced gravitational constant can, with a suitable choice of the coupling function, increase as one dates back.

scholarly journals Static solutions in the Freund – Nambu scalar-tensor theory of gravitation

2021 ◽  
Vol 57 (4) ◽  
pp. 464-469
Author(s):  
Yu. P. Vyblyi ◽  
O. G. Kurguzova
Keyword(s):  
Einstein Equations ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
Axially Symmetric ◽  
Field Equations ◽  
Tensor Theory ◽  
Static Solutions ◽  
Theory Of Gravitation

Herein, the system of Einstein equations and the equation of the Freund – Nambu massless scalar field for static spherically symmetric and axially symmetric fields are considered. It is shown that this system of field equations decouples into gravitational and scalar subsystems. In the second post-Newtonian approximation, the solutions for spherically symmetric and slowly rotating sources are obtained. The application of the obtained solutions to astrophysical problems is discussed.

scholarly journals PARAMETRIC INSTABILITY IN SCALAR GRAVITATIONAL FIELDS

2012 ◽  
Vol 27 (24) ◽  
pp. 1230023 ◽  
Author(s):  
TREVOR B. DAVIES ◽  
CHARLES H.-T. WANG ◽  
ROBERT BINGHAM ◽  
J. TITO MENDONÇA
Keyword(s):  
Gravitational Field ◽  
Field Effect ◽  
Strong Field ◽  
Parametric Instability ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
Subsequent Work ◽  
Dynamical Mechanism ◽  
Gravitational Fields ◽  
Tensor Theory

We present a brief review on a new dynamical mechanism for a strong field effect in scalar–tensor theory. Starting with a summary of the essential features of the theory and subsequent work by several authors, we analytically investigate the parametric excitation of a scalar gravitational field in a spherically symmetric radially pulsating neutron star.

scholarly journals Plane Symmetric Solutions of a Scalar-Tensor Theory of Gravitation

1977 ◽  
Vol 30 (1) ◽  
pp. 109 ◽  
Author(s):  
DRK Reddy
Keyword(s):  
General Relativity ◽  
Empty Space ◽  
Scalar Fields ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Plane Symmetric ◽  
Zero Mass ◽  
Tensor Theory ◽  
Special Cases ◽  
Theory Of Gravitation

Plane symmetric solutions of a scalar-tensor theory proposed by Dunn have been obtained. These solutions are observed to be similar to the plane symmetric solutions of the field equations corresponding to zero mass scalar fields obtained by Patel. It is found that the empty space-times of general relativity discussed by Taub and by Bera are obtained as special cases.

scholarly journals Extremal Cosmological Black Holes in Horndeski Gravity and the Anti-Evaporation Regime

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 210
Author(s):  
Ismael Ayuso ◽  
Diego Sáez-Chillón Gómez
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmological Constant ◽  
Linear Order ◽  
Scalar Tensor Theory ◽  
De Sitter ◽  
Tensor Theory ◽  
Effective Cosmological Constant ◽  
Cosmological Black Holes ◽  
Extremal Black Holes

Extremal cosmological black holes are analysed in the framework of the most general second order scalar-tensor theory, the so-called Horndeski gravity. Such extremal black holes are a particular case of Schwarzschild-De Sitter black holes that arises when the black hole horizon and the cosmological one coincide. Such metric is induced by a particular value of the effective cosmological constant and is known as Nariai spacetime. The existence of this type of solutions is studied when considering the Horndeski Lagrangian and its stability is analysed, where the so-called anti-evaporation regime is studied. Contrary to other frameworks, the radius of the horizon remains stable for some cases of the Horndeski Lagrangian when considering perturbations at linear order.

scholarly journals Non-Riemannian description of Robinson–Trautman spacetimes in Brans–Dicke theory of gravity

2019 ◽  
Vol 28 (04) ◽  
pp. 1950070
Author(s):  
Muzaffer Adak ◽  
Tekin Dereli ◽  
Yorgo Şenikoğlu
Keyword(s):  
Scalar Field ◽  
Differential Forms ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Exterior Differential ◽  
Tensor Theory ◽  
Theory Of Gravitation ◽  
Theory Of Gravity ◽  
Future Reference

The variational field equations of Brans–Dicke scalar-tensor theory of gravitation are given in a non-Riemannian setting in the language of exterior differential forms over four-dimensional spacetimes. A conformally rescaled Robinson–Trautman metric together with the Brans–Dicke scalar field are used to characterize algebraically special Robinson–Trautman spacetimes. All the relevant tensors are worked out in a complex null basis and given explicitly in an appendix for future reference. Some special families of solutions are also given and discussed.

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