Egyptian Relativity Group ERG

Al Jīzah, Egypt

Egyptian Relativity Group ERG

Al Jīzah, Egypt
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Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
Gravitation and Cosmology | Year: 2017

New non-vacuum spherically symmetric solutions in (1+4)-dimensional space-time are derived using the field equations of f(T) theory, where T is the torsion scalar defined as T=defTμνρSμνρ. The energy density, radial and transversal pressures in these solutions are shown to satisfy the energy conditions. Other interesting solutions are obtained under the constraint of vanishing radial pressure for different choices of f(T). Impositions are provided to reproduce the (1+4)-dimensional AdS-Schwarzschild solution. In the quadratic case, i.e., f(T) ∝ T2, other impositions are derived and have shown to satisfy the non-diagonal components of the field equations of f(T) theory. The physics relevant to the resulting models is discussed. © 2017, Pleiades Publishing, Ltd.


Wanas M.I.,The British University in Egypt | Wanas M.I.,Egyptian Relativity Group ERG | Youssef N.L.,Cairo University | Youssef N.L.,Egyptian Relativity Group ERG | And 2 more authors.
Classical and Quantum Gravity | Year: 2010

In this paper, we construct a field theory unifying gravity and electromagnetism in the context of extended absolute parallelism (EAP) geometry. This geometry combines, within its structure, the geometric richness of the tangent bundle and the mathematical simplicity of absolute parallelism (AP) geometry. The constructed field theory is a generalization of the generalized field theory (GFT) formulated by Mikhail and Wanas. The theory obtained is purely geometric. The horizontal (resp. vertical) field equations are derived by applying the Euler-Lagrange equations to an appropriate horizontal (resp. vertical) scalar Lagrangian. The symmetric part of the resulting horizontal (resp. vertical) field equations gives rise to a generalized form of Einstein's field equations in which the horizontal (resp. vertical) energy-momentum tensor is purely geometric. The skew-symmetric part of the resulting horizontal (resp. vertical) field equations gives rise to a generalized form of Maxwell equations in which the electromagnetic field is purely geometric. Some interesting special cases, which reveal the role of the nonlinear connection in the obtained field equations, are examined. Finally, the condition under which our constructed field equations reduce to the GFT is explicitly established. © 2010 IOP Publishing Ltd.


Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
Journal of the Physical Society of Japan | Year: 2014

A tetrad field, having one unknown function of radial coordinate r and an angle Φ which is a function of the azimuthal angle Φ, is applied to the field equation of modified teleparallel theory of gravity with cosmological constant. Exact vacuum solution is derived whose scalar torsion, T = Tα uv Suv α , (where Tα uv is the torsion tensor and Suv α is a tensor defined in terms of the contortion and torsion tensors), is vanishing. When the angle φ coincides with the polar angle (-φ), another solution is derived whose scalar torsion is constant. The space-time of the derived solutions is rewritten as a multiplication of two matrices: The first matrix is a special case of Euler's angle "so(3)" while the second matrix represents the square root of the spherically-symmetric-dS metric. © 2014 The Physical Society of Japan.


Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
Indian Journal of Physics | Year: 2015

A tetrad field, which gives Schwarzschild-NUT-AdS metric, is provided. We calculate the total conserved charges of this tetrad. This is done by using “regularization through relocalization” for the first time. This method gives the correct value of the total charge of Schwarzschild-NUT-AdS space–time, which depends on the gravitational mass of the system. We show that the NUT parameter has no physical meaning on the conserved quantities of the Schwarzschild-NUT-AdS space–time. © 2015, Indian Association for the Cultivation of Science.


Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
Astrophysics and Space Science | Year: 2016

We have derived D-dimension rotating charged black-holes with a flat horizon in the framework of Maxwell–Weitzenböck geometry. We have discussed the singularities of these black holes using the invariants of torsion and curvature and shown that the invariants of the torsion have more singularities than those of curvature. To investigate the physics of the derived black holes we have used the Einstein–Cartan geometry to calculate the conserved quantities. From these calculations, we have analyzed the physical meaning of the constants of integration. © 2016, Springer Science+Business Media Dordrecht.


Wanas M.I.,Cairo University | Wanas M.I.,Egyptian Relativity Group ERG | Wanas M.I.,The British University in Egypt | Ammar S.A.,Ain Shams University
Central European Journal of Physics | Year: 2013

The present work represents a step in dealing with stellar structure using a pure geometric approach. Geometric field theory is used to construct a model for a spherically symmetric configuration. In this case, two solutions have been obtained for the field equations. The first represents an interior solution which may be considered as a pure geometric one in the sense that the tensor describing the material distributions is not a phenomenological object, but a part of the geometric structure used. A general equation of state for a perfect fluid, is obtained from, and not imposed on, the model. The second solution gives rise to Schwarzschild exterior field in its isotropic form. The two solutions are matched, at a certain boundary, to evaluate the constants of integration. The interior solution obtained shows that there are different zones characterizing the configuration: a central radiation dominant zone, a probable convection zone as a physical interpretation of the singularity of the model, and a corona like zone. The model may represent a type of main sequence stars. The present work shows that Einstein's geometerization scheme can be extended to gain more physical information within material distribution, with some advantages. © 2013 Versita Warsaw and Springer-Verlag Wien.


Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
International Journal of Theoretical Physics | Year: 2014

The field equation of higher dimensions theory, have been applied in the area of cosmology. The resulting differential equations are solved for open and closed. We derive a relation between the Einstein constant G(t) and the cosmological constant Λ(t) from the conservation law Tμ ν =0. We give a specific form of Λ(t) to solve the non-linear differential equations. Some cosmological parameters are calculated and some relevant cosmological problems are discussed. © 2014, Springer Science+Business Media New York.


Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,Egyptian Relativity Group ERG
Astrophysics and Space Science | Year: 2013

A general tetrad fields, with an arbitrary function of radial coordinate, preserving spherical symmetry, is provided. Such tetrad is split into two matrices: The first matrix represents a Local Lorentz Transformation (LLT), which contains an arbitrary function. The second matrix represents a proper tetrad fields which satisfy the field equations of f(T) gravitational theory. This general tetrad is applied to the field equations of f(T). We derive a solution with one constant of integration to the resulting field equations of f(T). This solution gives a vanishing value of the scalar torsion. We calculate the energy associated with this solution to investigate what is the nature of the constant of integration. © 2013 Springer Science+Business Media Dordrecht.


Nashed G.G.L.,King Faisal University | Nashed G.G.L.,Ain Shams University | Nashed G.G.L.,The British University in Egypt | Nashed G.G.L.,Egyptian Relativity Group ERG
Chinese Physics Letters | Year: 2012

A new solution with constant torsion is derived using the field equations of f(T). Asymptotic forms of energy density, radial and transversal pressures are shown to meet the standard energy conditions, i.e., weak and null energy conditions according to some restrictions on T 0, f(T 0) and f T(T 0). Other solutions are obtained for vanishing radial pressure and for specific choices of f(T). The physics relevant to the resulting models is discussed. © 2012 Chinese Physical Society and IOP Publishing Ltd.


Wanas M.I.,Cairo University | Wanas M.I.,Egyptian Relativity Group ERG | Hassan H.A.,Egyptian Relativity Group ERG
International Journal of Theoretical Physics | Year: 2014

Inthe present work we show that the existence of non-vanishing torsion field may solve, at least, one of the problems FRW-cosmology, the particle horizons problem. The field equations of general relativity (GR) are written in a space having non-vanishing torsion, the absolute parallelism (AP) space. An AP-Structure, satisfying the cosmological principle, is used to construct a world model. Energy density and pressure, purely induced by torsion, are defined from the building blocks of the AP-geometry using GR. When these quantities are used in the FRW-dynamical equations, we get a world model free from particle horizons. © 2014, Springer Science+Business Media New York.

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