scholarly journals Exact Relativistic Magnetized Haloes around Rotating Disks

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Antonio C. Gutiérrez-Piñeres ◽  
Abraão J. S. Capistrano
Keyword(s):  
Charged Particle ◽  
Energy Momentum Tensor ◽  
Rotating Disk ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Rotating Disks ◽  
Relativistic Model ◽  
Asymptotically Flat ◽  
Relativistic Treatment ◽  
Formation And Evolution

The study of the dynamics of magnetic fields in galaxies is one of important problems in formation and evolution of galaxies. In this paper, we present the exact relativistic treatment of a rotating disk surrounded by a magnetized material halo. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.

Study of gravitational decoupled anisotropic solution

2019 ◽  
Vol 28 (16) ◽  
pp. 2040004
Author(s):  
M. Sharif ◽  
Sobia Sadiq
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Anisotropic Model ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Spherically Symmetric Solution ◽  
Gravitational Source ◽  
The Stability

This paper formulates the exact static anisotropic spherically symmetric solution of the field equations through gravitational decoupling. To accomplish this work, we add a new gravitational source in the energy–momentum tensor of a perfect fluid. The corresponding field equations, hydrostatic equilibrium equation as well as matching conditions are evaluated. We obtain the anisotropic model by extending the known Durgapal and Gehlot isotropic solution and examined the physical viability as well as the stability of the developed model. It is found that the system exhibits viable behavior for all fluid variables as well as energy conditions and the stability criterion is fulfilled.

scholarly journals Bounds on higher derivative f(R,□R,T) models from energy conditions

2019 ◽  
Vol 34 (11) ◽  
pp. 1950082 ◽  
Author(s):  
M. Ilyas ◽  
Z. Yousaf ◽  
M. Z. Bhatti
Keyword(s):  
Perfect Fluid ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Higher Derivative ◽  
Derivative Formula ◽  
Cosmological Solutions ◽  
Walker Metric ◽  
Cosmic Parameters

This paper studies the viable regions of some cosmic models in a higher derivative [Formula: see text] theory with the help of energy conditions (where [Formula: see text], [Formula: see text] and [Formula: see text] are the Ricci scalar, d’Alembert’s operator and trace of energy–momentum tensor, respectively). For this purpose, we assume a flat Friedmann–Lemaître–Robertson–Walker metric which is assumed to be filled with perfect fluid configurations. We take two distinct realistic models that might be helpful to explore stable regimes of cosmological solutions. After taking some numerical values of cosmic parameters, like crackle, snap, jerk (etc.) as well as viable constraints from energy conditions, the viable zones for the under observed [Formula: see text] models are examined.

scholarly journals Rotating thin shells in (2 + 1)-dimensional asymptotically AdS spacetimes: Mechanical properties, machian effects, and energy conditions

2015 ◽  
Vol 24 (09) ◽  
pp. 1542022 ◽  
Author(s):  
José P. S. Lemos ◽  
Francisco J. Lopes ◽  
Masato Minamitsuji
Keyword(s):  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Thin Shells ◽  
Dominant Energy Condition ◽  
Junction Conditions ◽  
Rest Energy ◽  
Inertial Frames ◽  
Ads Spacetime

In this paper, a rotating thin shell in a (2 + 1)-dimensional asymptotically AdS spacetime is studied. The spacetime exterior to the shell is the rotating BTZ spacetime and the interior is the empty spacetime with a cosmological constant. Through the Einstein equation in (2 + 1) dimensions and the corresponding junction conditions we calculate the dynamical relevant quantities, namely, the rest energy–density, the pressure, and the angular momentum flux density. We also analyze the matter in a frame where its energy–momentum tensor has a perfect fluid form. In addition, we show that Machian effects, such as the dragging of inertial frames, also occur in rotating (2 + 1)-dimensional spacetimes. The weak and the dominant energy condition for these shells are discussed.

Wormhole models in f(R,T) gravity

2019 ◽  
Vol 28 (15) ◽  
pp. 1950172 ◽  
Author(s):  
Emilio Elizalde ◽  
Martiros Khurshudyan
Keyword(s):  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Energy Condition ◽  
Physical Nature ◽  
Radial Pressure ◽  
Momentum Tensor ◽  
Matter Content ◽  
Energy Conditions ◽  
Dominant Energy Condition ◽  
The Stability

Models of static wormholes within the [Formula: see text] extended theory of gravity are investigated, in particular the family [Formula: see text], with [Formula: see text] being the trace of the energy–momentum tensor. Models corresponding to different relations for the pressure components (radial and lateral), and several equations-of-state (EoS), reflecting different matter content, are worked out explicitly. The solutions obtained for the shape functions of the generated wormholes obey the necessary metric conditions, as manifested in other studies in the literature. The respective energy conditions reveal the physical nature of the wormhole models thus constructed. It is found, in particular, that for each of those considered, the parameter space can be divided into different regions, in which the exact wormhole solutions fulfill the null energy conditions (NEC) and the weak energy conditions (WEC), respectively, in terms of the lateral pressure. Moreover, the dominant energy condition (DEC) in terms of both pressures is also valid, while [Formula: see text]. A similar solution for the theory [Formula: see text] is found numerically, where [Formula: see text] and [Formula: see text] are either constant or functions of [Formula: see text], leading to the result that the NEC in terms of the radial pressure is also valid. For nonconstant [Formula: see text] models, attention is focused on the behavior [Formula: see text]. To finish, the question is addressed, how [Formula: see text] will affect the wormhole solutions corresponding to fluids of the form [Formula: see text], in the three cases such as NEC, WEC and DEC. Issues concerning the nonconservation of the matter energy–momentum tensor, the stability of the solutions obtained, and the observational possibilities for testing these models are discussed in Sec. 6.

WORMHOLES OF K-ESSENCE IN ARBITRARY SPACE–TIME DIMENSIONS

2008 ◽  
Vol 23 (20) ◽  
pp. 3165-3175 ◽  
Author(s):  
J. ESTEVEZ-DELGADO ◽  
T. ZANNIAS
Keyword(s):  
Energy Momentum Tensor ◽  
Opposite Sign ◽  
Momentum Tensor ◽  
Space Time ◽  
Parameter Family ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Asymptotically Flat ◽  
Arbitrary Space ◽  
Two Parameter

We consider a K-essence involving a massless scalar field Φ minimally coupled to Einstein gravity in D ≥ 4 space–time dimensions. This theory admits a two-parameter family of spherical wormholes representing two asymptotically-flat universes connected via a (D-2)-dimensional spherical throat. The ADM masses of the two ends are unequal and of opposite sign except for a one-parameter family where both ends possess vanishing ADM masses. By cut and paste techniques, we construct a two-parameter family of wormholes where the ends possess equal and positive ADM masses but the throat is a (D-1)-dimensional thin-shell. The structure of the surface energy–momentum tensor is also analyzed.

Wormholes supported by f(𝒢) gravity

2014 ◽  
Vol 24 (01) ◽  
pp. 1550003 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Power Law ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Momentum Tensor ◽  
Red Shift ◽  
Energy Conditions ◽  
Shift Function ◽  
Effective Energy ◽  
Barotropic Fluids

This paper is devoted to study the traversable wormhole (WH) solutions in the context of f(𝒢) gravity. For this purpose, we consider the viable power-law form f(𝒢) = a𝒢n as well as specific variable red-shift function and investigate WH geometries for traceless, isotropic as well as barotropic fluids. It is found that in each case, the effective energy-momentum tensor violates the null energy condition throughout the WH throat. We also check the null as well as weak energy conditions for ordinary matter. We conclude that physical acceptable WH solutions exist in certain regions only for radial barotropic case while the range of these regions increases and decreases as the power of 𝒢 increases in even and odd manner, respectively.

scholarly journals FAMILY OF ROTATING ANISOTROPIC FLUID SOLUTIONS WHICH MATCH TO KERR'S SOLUTION

2013 ◽  
Vol 22 (07) ◽  
pp. 1350051 ◽  
Author(s):  
E. KYRIAKOPOULOS
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Thin Shells ◽  
Closed Surfaces ◽  
Oblate Spheroids ◽  
The Family ◽  
Proper Values ◽  
Tensor Formula

We present a family of exact rotating anisotropic fluid solutions, which satisfy all energy conditions for certain values of their parameters. The components of the Ricci tensor Rμν the eigenvalues of the tensor [Formula: see text] and the energy–momentum tensor Tμν of the solutions are given explicitly. All members of the family have the ring singularity of Kerr's solution and most of them have one or two more singularities. The solutions can be matched to the solution of Kerr on three closed surfaces, which for proper values of the parameters of the solutions approximate oblate spheroids. All matching surfaces are thin shells. For some values of a constant the surface density in one of them is positive everywhere and in this surface and in its interior all energy conditions are satisfied.

scholarly journals Tractor Beams, Pressor Beams and Stressor Beams in General Relativity

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 271
Author(s):  
Jessica Santiago ◽  
Sebastian Schuster ◽  
Matt Visser
Keyword(s):  
General Relativity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Einstein Equations ◽  
Energy Conditions ◽  
Frequent Use ◽  
Advanced Civilization

The metrics of general relativity generally fall into two categories: those which are solutions of the Einstein equations for a given source energy-momentum tensor and the “reverse engineered” metrics—metrics bespoke for a certain purpose. Their energy-momentum tensors are then calculated by inserting these into the Einstein equations. This latter approach has found frequent use when confronted with creative input from fiction, wormholes and warp drives being the most famous examples. In this paper, we again take inspiration from fiction and see what general relativity can tell us about the possibility of a gravitationally induced tractor beam. We base our construction on warp drives and show how versatile this ansatz alone proves to be. Not only can we easily find tractor beams (attracting objects), but repulsor/pressor beams are just as attainable, and a generalization to “stressor” beams is seen to present itself quite naturally. We show that all of these metrics would violate various energy conditions. This provides an opportunity to ruminate on the meaning of energy conditions as such and what we can learn about whether an arbitrarily advanced civilization might have access to such beams.

scholarly journals Traversable wormholes in the traceless f(R,T) gravity

2021 ◽  
pp. 2150100
Author(s):  
Parbati Sahoo ◽  
P. H. R. S. Moraes ◽  
Marcelo M. Lapola ◽  
P. K. Sahoo
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Shape Functions ◽  
Anisotropic Matter ◽  
Traversable Wormholes ◽  
Theory Of Gravitation ◽  
Geometrical Term

Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein’s General Theory of Relativity and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the present sense, by “exotic matter” we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of traversable wormholes (i.e. wormholes that can be safely crossed) within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action, namely the traceless [Formula: see text] theory of gravitation, with [Formula: see text] and [Formula: see text] being, respectively, the Ricci scalar and trace of the energy–momentum tensor. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, namely redshift and shape functions. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed.

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.

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