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Einstein Equations via Null Surfaces

100%
Iyer S., Newman E., Kozameh C.
Acta Physica Polonica A
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1994
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vol. 85
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issue 4
647-654
EN
We present a version of the vacuum Einstein equations where the field equations are defined for cross-sections of a line bundle over the sphere and where the manifold of solutions is four-dimensional and defines the space-time itself. The cross-sections themselves become the characteristic surfaces of the space-time.
2
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Wormhole Solution and Energy in Teleparallel Theory of Gravity

51%
Nashed G.
Acta Physica Polonica A
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2007
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vol. 111
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issue 2
201-213
EN
An exact solution is obtained in the tetrad theory of gravitation. This solution is characterized by two parameters k_1, k_2 of spherically symmetric static Lorentzian wormhole which is obtained as a solution of the equation ρ= ρ_t=0 with ρ=T_{i,j}u^iu^j, ρ_t =(T_{ij}-1/2Tg_{ij}) u^iu^j, where u^iu_i=-1. From this solution which contains an arbitrary function we can generate the other two solutions obtained before. The associated metric of this space-time is a static Lorentzian wormhole and it includes the Schwarzschild black hole, a family of naked singularity and a disjoint family of Lorentzian wormholes. Calculating the energy content of this tetrad field and using the gravitational energy momentum given by Møller in the teleparallel space-time we find that the resulting form depends on the arbitrary function and does not depend on the two parameters k_1 and k_2 characterizing the wormhole. Using the regularized expression of the gravitational energy momentum we get the value of energy which does not depend on the arbitrary function.
3
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Stability of Reissner-Nordström Black Hole

51%
Nashed G.
Acta Physica Polonica A
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2007
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vol. 112
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issue 1
13-21
EN
The singularity of the solutions obtained before in the teleparallel theory of gravitation is studied. Also the stability of these solutions is studied using the equations of geodesic deviation. The condition of stability is obtained. From this condition the stability of the Schwarzschild solution can be obtained.
4
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f-symbols in Robertson-Walker space-time

38%
Popa F., Tintareanu-Mircea O.
Open Physics
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2005
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vol. 3
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issue 2
221-228
EN
In a Robertson-Walker space-time, a spinning particle model is investigated. It is shown that in a stationary case a class of new structures called f-symbols exists ¢ Central European Science Journals. All rights reserved.
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