scholarly journals Static cylindrical symmetric solutions in the Einstein-Aether theory

2021 ◽  
Author(s):  
R. Chan ◽  
M. F. A. da Silva
Keyword(s):  
General Relativity ◽  
Cylindrical Symmetry ◽  
Maximum Radius ◽  
Cylindrically Symmetric ◽  
Test Particles ◽  
Symmetric Spacetime

In this work, we present all the possible solutions for a static cylindrical symmetric spacetime in the Einstein-Aether (EA) theory. As far as we know, this is the first work in the literature that considers cylindrically symmetric solutions in the theory of EA. One of these solutions is the generalization in EA theory of the Levi-Civita (LC) spacetime in General Relativity (GR) theory. We have shown that this generalized LC solution has unusual geodesic properties, depending on the parameter [Formula: see text] of the aether field. The circular geodesics are the same of the GR theory, no matter the values of [Formula: see text]. However, the radial and [Formula: see text]-direction geodesics are allowed only for certain values of [Formula: see text] and [Formula: see text]. The [Formula: see text]-direction geodesics are restricted to an interval of [Formula: see text] different from those predicted by the GR and the radial geodesics show that the motion is confined between the origin and a maximum radius. The latter is not affected by the aether field but the velocity and acceleration of the test particles are besides, for [Formula: see text], when the cylindrical symmetry is preserved, this spacetime is singular at the axis [Formula: see text], although for [Formula: see text] exists interval of [Formula: see text] where the spacetime is not singular, which is completely different from that one obtained with the GR theory, where the axis [Formula: see text] is always singular.

scholarly journals CYLINDRICALLY SYMMETRIC SPINNING BRANS–DICKE SPACE–TIMES WITH CLOSED TIMELIKE CURVES

1999 ◽  
Vol 14 (17) ◽  
pp. 1105-1111 ◽  
Author(s):  
LUIS A. ANCHORDOQUI ◽  
SANTIAGO E. PEREZ BERGLIAFFA ◽  
MARTA L. TROBO ◽  
GRACIELA S. BIRMAN
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Cylindrical Symmetry ◽  
Space Time ◽  
Rigid Rotation ◽  
Closed Timelike Curves ◽  
New Exact Solutions ◽  
Cylindrically Symmetric

We present here three new exact solutions of Brans–Dicke theory for a stationary geometry with cylindrical symmetry in the presence of matter in rigid rotation with [Formula: see text]. All the solutions have eternal closed timelike curves in some region of space–time which has a size that depends on ω. Moreover, two of them do not go over a solution of general relativity in the limit ω→∞.

scholarly journals EXACT SOLUTION FOR THE MASSLESS CYLINDRICALLY SYMMETRIC SCALAR FIELD IN GENERAL RELATIVITY, WITH COSMOLOGICAL CONSTANT

2009 ◽  
Vol 24 (31) ◽  
pp. 5991-6000 ◽  
Author(s):  
D. MOMENI ◽  
H. MIRAGHAEI
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Cylindrical Symmetry ◽  
Cosmological Models ◽  
Cyclic Universe ◽  
Cylindrically Symmetric

In this paper, we present a new exact solution for scalar field with cosmological constant in cylindrical symmetry. Associated cosmological models, including a model that describes a cyclic universe, are discussed.

Cylindrical waves in general relativity

1986 ◽  
Vol 408 (1835) ◽  
pp. 209-232 ◽  
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Energy Density ◽  
Perfect Fluid ◽  
Maxwell Equations ◽  
Cylindrical Symmetry ◽  
Hamiltonian Density ◽  
Cylindrical Waves ◽  
Cylindrically Symmetric ◽  
Set Up

A convenient framework is set up for constructing cylindrically symmetric solutions of the Einstein and the Einstein—Maxwell equations, and it is shown how a Hamiltonian density can be defined for space-times with cylindrical symmetry. Solutions are obtained that represent stationary monochromatic waves and satisfy all the requisite conditions of regularity. The case when the gravitational field is coupled with a perfect fluid in which the energy density is equal to the pressure is also briefly considered.

scholarly journals WEYL GEOMETRY AS CHARACTERIZATION OF SPACE-TIME

2011 ◽  
Vol 03 ◽  
pp. 87-97 ◽  
Author(s):  
F. P. POULIS ◽  
J. M. SALIM
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Riemannian Geometry ◽  
Axiomatic Approach ◽  
Space Time ◽  
Weyl Geometry ◽  
Test Particles ◽  
Variational Formalism ◽  
Physical Fields

Motivated by an axiomatic approach to characterize space-time it is investigated a reformulation of Einstein's gravity where the pseudo-riemannian geometry is substituted by a Weyl one. It is presented the main properties of the Weyl geometry and it is shown that it gives extra contributions to the trajectories of test particles, serving as one more motivation to study general relativity in Weyl geometry. It is introduced its variational formalism and it is established the coupling with other physical fields in such a way that the theory acquires a gauge symmetry for the geometrical fields. It is shown that this symmetry is still present for the red-shift and it is concluded that for cosmological models it opens the possibility that observations can be fully described by the new geometrical scalar field. It is concluded then that this reformulation, although representing a theoretical advance, still needs a complete description of their objects.

scholarly journals Vaidya solutions in general covariant Hořava–Lifshitz gravity without projectability: Infrared limit

2014 ◽  
Vol 23 (08) ◽  
pp. 1450068 ◽  
Author(s):  
O. Goldoni ◽  
M. F. A. da Silva ◽  
G. Pinheiro ◽  
R. Chan
Keyword(s):  
General Relativity ◽  
Gauge Field ◽  
Radiation Field ◽  
Relativity Theory ◽  
Covariant Theory ◽  
Spherically Symmetric ◽  
Theory U ◽  
General Relativity Theory ◽  
Infrared Limit ◽  
Symmetric Spacetime

In this paper, we have studied nonstationary radiative spherically symmetric spacetime, in general covariant theory (U(1) extension) of Hořava–Lifshitz (HL) gravity without the projectability condition and in the infrared (IR) limit. The Newtonian prepotential φ was assumed null. We have shown that there is not the analogue of the Vaidya's solution in the Hořava–Lifshitz Theory (HLT), as we know in the General Relativity Theory (GRT). Therefore, we conclude that the gauge field A should interact with the null radiation field of the Vaidya's spacetime in the HLT.

scholarly journals KINKS, ENERGY CONDITIONS AND CLOSED TIMELIKE CURVES

2000 ◽  
Vol 09 (05) ◽  
pp. 531-541 ◽  
Author(s):  
PEDRO F. GONZÁLEZ-DÍAZ
Keyword(s):  
Energy Condition ◽  
Weak Energy Condition ◽  
Energy Conditions ◽  
Closed Timelike Curves ◽  
Causality Violation ◽  
Incoherent Radiation ◽  
Cylindrically Symmetric ◽  
Cylindrically Symmetric Spacetime ◽  
Geodesically Complete ◽  
Symmetric Spacetime

A link between the possibility of extending a geodesically incomplete kinked spacetime to a spacetime which is geodesically complete and the energy conditions is discussed for the case of a cylindrically-symmetric spacetime kink. It is concluded that neither the strong nor the weak energy condition can be satisfied in the four-dimensional example, though the latter condition may survive on the transversal sections of such a spacetime. It is also shown that the matter which propagates quantum-mechanically in a kinked spacetime can always be trapped by closed timelike curves, but signaling connections between that matter and any possible observer can only be made of totally incoherent radiation, so preventing observation of causality violation.

GEOMETRY OF SPACETIME AND FINSLER GEOMETRY

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1678-1685 ◽  
Author(s):  
REZA TAVAKOL
Keyword(s):  
General Relativity ◽  
String Theory ◽  
Riemannian Geometry ◽  
Lorentz Invariance ◽  
Finsler Geometry ◽  
Spacetime Geometry ◽  
Test Particles ◽  
Light Rays ◽  
Recent Developments ◽  
Underlying Geometry

A central assumption in general relativity is that the underlying geometry of spacetime is pseudo-Riemannian. Given the recent attempts at generalizations of general relativity, motivated both by theoretical and observational considerations, an important question is whether the spacetime geometry can also be made more general and yet still remain compatible with observations? Here I briefly summarize some earlier results which demonstrate that there are special classes of Finsler geometry, which is a natural metrical generalization of the Riemannian geometry, that are strictly compatible with the observations regarding the motion of idealised test particles and light rays. I also briefly summarize some recent attempts at employing Finsler geometries motivated by more recent developments such as those in String theory, whereby Lorentz invariance is partially broken.

scholarly journals Anisotropic compact stars in higher-order curvature theory

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
G. G. L. Nashed ◽  
S. D. Odintsov ◽  
V. K. Oikonomou
Keyword(s):  
General Relativity ◽  
Differential Equations ◽  
Higher Order ◽  
Specific Form ◽  
Ricci Scalar ◽  
Spherically Symmetric ◽  
Curvature Theory ◽  
Anisotropic Star ◽  
Symmetric Spacetime ◽  
Spherically Symmetric Spacetime

AbstractIn this paper we shall consider spherically symmetric spacetime solutions describing the interior of stellar compact objects, in the context of higher-order curvature theory of the $${{\mathrm {f(R)}}}$$ f ( R ) type. We shall derive the non-vacuum field equations of the higher-order curvature theory, without assuming any specific form of the $${{\mathrm {f(R)}}}$$ f ( R ) theory, specifying the analysis for a spherically symmetric spacetime with two unknown functions. We obtain a system of highly non-linear differential equations, which consists of four differential equations with six unknown functions. To solve such a system, we assume a specific form of metric potentials, using the Krori–Barua ansatz. We successfully solve the system of differential equations, and we derive all the components of the energy–momentum tensor. Moreover, we derive the non-trivial general form of $${{\mathrm {f(R)}}}$$ f ( R ) that may generate such solutions and calculate the dynamic Ricci scalar of the anisotropic star. Accordingly, we calculate the asymptotic form of the function $${\mathrm {f(R)}}$$ f ( R ) , which is a polynomial function. We match the derived interior solution with the exterior one, which was derived in [1], with the latter also resulting to a non-trivial form of the Ricci scalar. Notably but rather expected, the exterior solution differs from the Schwarzschild one in the context of general relativity. The matching procedure will eventually relate two constants with the mass and radius of the compact stellar object. We list the necessary conditions that any compact anisotropic star must satisfy and explain in detail that our model bypasses all of these conditions for a special compact star $$\textit{Her X--1}$$ Her X - - 1 , which has an estimated mass and radius $$(mass = 0.85 \pm 0.15M_{\circledcirc }\ and\ radius = 8.1 \pm 0.41~\text {km}$$ ( m a s s = 0.85 ± 0.15 M ⊚ a n d r a d i u s = 8.1 ± 0.41 km ). Moreover, we study the stability of this model by using the Tolman–Oppenheimer–Volkoff equation and adiabatic index, and we show that the considered model is different and more stable compared to the corresponding models in the context of general relativity.

scholarly journals A type of Levi–Civita solution in modified Gauss–Bonnet gravity

2014 ◽  
Vol 92 (2) ◽  
pp. 173-176 ◽  
Author(s):  
M.E. Rodrigues ◽  
M.J.S. Houndjo ◽  
D. Momeni ◽  
R. Myrzakulov
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Perfect Fluid ◽  
Cosmic String ◽  
Coupling Parameter ◽  
Vacuum Solution ◽  
Einstein Gravity ◽  
Parameter Family ◽  
Bonnet Gravity ◽  
Cylindrically Symmetric

Herein we obtain an exact solution for cylindrically symmetric modified Gauss–Bonnet gravity. This metric is a generalization of the vacuum solution of Levi–Civita in general relativity. It describes an isotropic perfect fluid one-parameter family of the gravitational configurations, which can be interpreted as the exterior metric of a cosmic string. By setting the Gauss–Bonnet coupling parameter to zero, we recover the vacuum solution in the Einstein gravity as well.

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