scholarly journals Curvature properties of Nariai spacetimes

2020 ◽  
Vol 17 (03) ◽  
pp. 2050034 ◽  
Author(s):  
Absos Ali Shaikh ◽  
Akram Ali ◽  
Ali H. Alkhaldi ◽  
Dhyanesh Chakraborty
Keyword(s):  
Covariant Derivative ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Topological Product ◽  
Geometric Structures ◽  
Type Formula ◽  
Curvature Tensors ◽  
Recurrent Type

This paper is concerned with the study of the geometry of (charged) Nariai spacetime, a topological product spacetime, by means of covariant derivative(s) of its various curvature tensors. It is found that on this spacetime the condition [Formula: see text] is satisfied and it also admits the pseudosymmetric type curvature conditions [Formula: see text] and [Formula: see text]. Moreover, it is 4-dimensional Roter type, [Formula: see text]-quasi-Einstein and generalized quasi-Einstein spacetime. The energy–momentum tensor is expressed explicitly by some 1-forms. It is worthy to see that a generalization of such topological product spacetime proposes to exist with a class of generalized recurrent type manifolds which is semisymmetric. It is observed that the rank of [Formula: see text], [Formula: see text], of Nariai spacetime (NS) is 0 whereas in case of charged Nariai spacetime (CNS) it is 2, which exhibits that effects of charge increase the rank of Ricci tensor. Also, due to the presence of charge in CNS, it gives rise to the proper pseudosymmetric type geometric structures.

scholarly journals A geometrical model for the evolution of spherical planetary nebulae based on thin-shell formalism

2021 ◽  
pp. 2150191
Author(s):  
Ibrahim Gullu ◽  
S. Habib Mazharimousavi ◽  
S. Danial Forghani
Keyword(s):  
Energy Density ◽  
Planetary Nebula ◽  
Thin Shell ◽  
Energy Momentum Tensor ◽  
Geometric Model ◽  
Geometrical Model ◽  
Momentum Tensor ◽  
Evolution Pattern ◽  
Simple Power Function ◽  
Curvature Tensors

A spherical planetary nebula is described as a geometric model. The nebula itself is considered as a thin-shell, which is visualized as a boundary of two spacetimes. The inner and outer curvature tensors of the thin-shell are found in order to get an expression of the energy-momentum tensor on the thin-shell. The energy density and pressure expressions are derived using the energy-momentum tensor. The time evolution of the radius of the thin-shell is obtained in terms of the energy density. The model is tested by using a simple power function for decreasing energy density and the evolution pattern of the planetary nebula is attained.

scholarly journals Curvature Properties of Generalized pp-Wave Metrics

2021 ◽  
Vol 45 (02) ◽  
pp. 237-258
Author(s):  
ABSOS ALI SHAIKH ◽  
TRAN QUOC BINH ◽  
HARADHAN KUNDU
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Sufficient Condition ◽  
Type Condition ◽  
Pure Radiation ◽  
Projective Curvature ◽  
Pp Wave ◽  
Codazzi Type ◽  
Curvature Tensors ◽  
Special Case

The main objective of the present paper is to investigate the curvature properties of generalized pp-wave metrics. It is shown that a generalized pp-wave spacetime is Ricci generalized pseudosymmetric, 2-quasi-Einstein and generalized quasi-Einstein in the sense of Chaki. As a special case it is shown that pp-wave spacetime is semisymmetric, semisymmetric due to conformal and projective curvature tensors, R-space by Venzi and satisfies the pseudosymmetric type condition P ⋅ P = −13Q(S,P). Again we investigate the sufficient condition for which a generalized pp-wave spacetime turns into pp-wave spacetime, pure radiation spacetime, locally symmetric and recurrent. Finally, it is shown that the energy-momentum tensor of pp-wave spacetime is parallel if and only if it is cyclic parallel. Again the energy momentum tensor is Codazzi type if it is cyclic parallel but the converse is not true as shown by an example. Finally, we make a comparison between the curvature properties of the Robinson-Trautman metric and generalized pp-wave metric.

Conformal Ricci collineations in LRS Bianchi type V spacetimes with perfect fluid matter

2017 ◽  
Vol 32 (24) ◽  
pp. 1750124 ◽  
Author(s):  
Fawad Khan ◽  
Tahir Hussain ◽  
Sumaira Saleem Akhtar
Keyword(s):  
Perfect Fluid ◽  
Ricci Tensor ◽  
Bianchi Type ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Ricci Collineations ◽  
Rotationally Symmetric ◽  
Fluid Matter ◽  
Type V ◽  
Bianchi Type V

Considering the perfect fluid as a source of energy–momentum tensor, we have classified locally rotationally symmetric (LRS) Bianchi type V spacetimes according to their conformal Ricci collineations (CRCs). It is shown that the LRS Bianchi type V spacetimes with perfect fluid matter admit 9- or 15-dimensional Lie algebra of CRCs when the Ricci tensor is non-degenerate, while the group of CRCs is infinite for degenerate Ricci tensor.

Homothetic Ricci collineations in non-static plane symmetric spacetimes with perfect fluid matter

2018 ◽  
Vol 15 (05) ◽  
pp. 1850075
Author(s):  
Tahir Hussain ◽  
Sumaira Saleem Akhtar
Keyword(s):  
Perfect Fluid ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Ricci Collineations ◽  
Plane Symmetric ◽  
Symmetric Spacetimes ◽  
Fluid Matter ◽  
Static Plane ◽  
Degenerate Cases

In this paper, we investigate homothetic Ricci collineations (HRCs) for non-static plane symmetric spacetimes. The source of the energy–momentum tensor is assumed to be a perfect fluid. Both degenerate as well as non-degenerate cases are considered and the HRC equations are solved in different cases. It is concluded that these spacetimes may possess 6, 7, 8, 10 or 11 HRCs in non-degenerate case, while they admit seven or infinite number of HRCs for degenerate Ricci tensor.

scholarly journals On Gödel-type solution in Rastall's gravity

2015 ◽  
Vol 30 (09) ◽  
pp. 1550039 ◽  
Author(s):  
A. F. Santos ◽  
S. C. Ulhoa
Keyword(s):  
Covariant Derivative ◽  
Energy Momentum Tensor ◽  
Quantum Effects ◽  
Momentum Tensor ◽  
Conserved Quantity ◽  
Ricci Scalar ◽  
Einstein’S Equations ◽  
Type Solution ◽  
Curved Spacetime ◽  
Einstein's Equations

Rastall's theory is a generalization of Einstein's equations in which the energy–momentum tensor is not a conserved quantity, its covariant derivative is proportional to the gradient of the Ricci scalar and this fact can be associated with quantum effects in curved spacetime. In this work we will go study the Rastall's gravity in the context of the Gödel-type universe.

scholarly journals Spacetimes Admitting Concircular Curvaure Tensor in f(R) Gravity

2022 ◽  
Vol 9 ◽  
Author(s):  
Uday Chand De ◽  
Sameh Shenawy ◽  
H. M. Abu-Donia ◽  
Nasser Bin Turki ◽  
Suliman Alsaeed ◽  
...  
Keyword(s):  
Energy Density ◽  
Perfect Fluid ◽  
Curvature Tensor ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Isotropic Pressure ◽  
Concircular Curvature Tensor ◽  
Fluid Spacetimes

The main object of this paper is to investigate spacetimes admitting concircular curvature tensor in f(R) gravity theory. At first, concircularly flat and concircularly flat perfect fluid spacetimes in fR gravity are studied. In this case, the forms of the isotropic pressure p and the energy density σ are obtained. Next, some energy conditions are considered. Finally, perfect fluid spacetimes with divergence free concircular curvature tensor in f(R) gravity are studied; amongst many results, it is proved that if the energy-momentum tensor of such spacetimes is recurrent or bi-recurrent, then the Ricci tensor is semi-symmetric and hence these spacetimes either represent inflation or their isotropic pressure and energy density are constants.

On a type of spacetime

2016 ◽  
Vol 14 (01) ◽  
pp. 1750003 ◽  
Author(s):  
Uday Chand De ◽  
Ljubica Velimirović ◽  
Sahanous Mallick
Keyword(s):  
Vector Field ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Flat Spacetime ◽  
Integral Curves ◽  
Conharmonic Curvature Tensor ◽  
Cyclic Parallel Ricci Tensor ◽  
Perfect Fluid Spacetime ◽  
Parallel Ricci Tensor

The object of the present paper is to study a spacetime admitting conharmonic curvature tensor and some geometric properties related to this spacetime. It is shown that in a conharmonically flat spacetime with cyclic parallel Ricci tensor, the energy–momentum tensor is cyclic parallel and conversely. Finally, we prove that for a radiative perfect fluid spacetime if the energy–momentum tensor satisfying the Einstein’s equations without cosmological constant is generalized recurrent, then the fluid has vanishing vorticity and the integral curves of the vector field [Formula: see text] are geodesics.

scholarly journals Matter may matter

2014 ◽  
Vol 23 (12) ◽  
pp. 1442016 ◽  
Author(s):  
Zahra Haghani ◽  
Tiberiu Harko ◽  
Hamid Reza Sepangi ◽  
Shahab Shahidi
Keyword(s):  
Gravitational Field ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Gravitational Theory ◽  
Momentum Tensor ◽  
Local Perturbations ◽  
Effective Lagrangian ◽  
Acceleration Of The Universe ◽  
The Stability ◽  
Matter Energy

We propose a gravitational theory in which the effective Lagrangian of the gravitational field is given by an arbitrary function of the Ricci scalar, the trace of the matter energy–momentum tensor, and the contraction of the Ricci tensor with the matter energy–momentum tensor. The matter energy–momentum tensor is generally not conserved, thus leading to the appearance of an extra-force, acting on massive particles in a gravitational field. The stability conditions of the theory with respect to local perturbations are also obtained. The cosmological implications of the theory are investigated, representing an exponential solution. Hence, a Ricci tensor–energy–momentum tensor coupling may explain the recent acceleration of the universe, without resorting to the mysterious dark energy.

CASIMIR EFFECT FOR THE ROBIN SURFACES IN STATIC ROBERTSON–WALKER SPACE–TIME

2011 ◽  
Vol 20 (02) ◽  
pp. 161-168 ◽  
Author(s):  
MOHAMMAD R. SETARE ◽  
M. DEHGHANI
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Casimir Effect ◽  
Vacuum Expectation ◽  
Robin Boundary Condition ◽  
Momentum Tensor ◽  
Space Time ◽  
Conformally Invariant ◽  
Time Space ◽  
Robin Boundary

We investigate the energy–momentum tensor for a massless conformally coupled scalar field in the region between two curved surfaces in k = -1 static Robertson–Walker space–time. We assume that the scalar field satisfies the Robin boundary condition on the surfaces. Robertson–Walker space–time space is conformally related to Rindler space; as a result we can obtain vacuum expectation values of the energy–momentum tensor for a conformally invariant field in Robertson–Walker space–time space from the corresponding Rindler counterpart by the conformal transformation.

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