Anisotropic spheres with uniform energy density in general relativity

1989 ◽  
Vol 21 (9) ◽  
pp. 899-905 ◽  
Author(s):  
S. D. Maharaj ◽  
R. Maartens
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Uniform Energy Density ◽  
Anisotropic Spheres

BOUNDS ON f(G) GRAVITY FROM ENERGY CONDITIONS

2010 ◽  
Vol 25 (27) ◽  
pp. 2325-2332 ◽  
Author(s):  
PUXUN WU ◽  
HONGWEI YU
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Modified Gravity ◽  
Energy Conditions ◽  
Model Parameters ◽  
Effective Energy ◽  
Raychaudhuri Equation ◽  
Accelerating Expansion

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρm + ρE and p → pm + pE, where ρE and pE are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

scholarly journals f(T) gravity and energy distribution in Landau–Lifshitz prescription

2018 ◽  
Vol 27 (04) ◽  
pp. 1850039 ◽  
Author(s):  
M. G. Ganiou ◽  
M. J. S. Houndjo ◽  
J. Tossa
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Energy Distribution ◽  
Cosmic String ◽  
Mass Formula ◽  
Plane Symmetric ◽  
Symmetric Metrics ◽  
Teleparallel Theory ◽  
Momentum Complex ◽  
Theory View

We investigate in this paper the Landau–Lifshitz energy distribution in the framework of [Formula: see text] theory view as a modified version of Teleparallel theory. From some important Teleparallel theory results on the localization of energy, our investigations generalize the Landau–Lifshitz prescription from the computation of the energy–momentum complex to the framework of [Formula: see text] gravity as it is done in the modified versions of General Relativity. We compute the energy density in the first step for three plane-symmetric metrics in vacuum. We find for the second metric that the energy density vanishes independently of [Formula: see text] models. We find that the Teleparallel Landau–Lifshitz energy–momentum complex formulations for these metrics are different from those obtained in General Relativity for the same metrics. Second, the calculations are performed for the cosmic string spacetime metric. It results that the energy distribution depends on the mass [Formula: see text] and the radius [Formula: see text] of cosmic string and it is strongly affected by the parameter of the considered quadratic and cubic [Formula: see text] models. Our investigation with this metric induces interesting results susceptible to be tested with some astrophysics hypothesis.

Signature of Topology of the Universe

2018 ◽  
Vol 2 (01) ◽  
Author(s):  
Vipin Kumar Sharma
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Local Geometry ◽  
Microwave Background ◽  
Main Motivation ◽  
And Topology ◽  
The Standard Model ◽  
Topology Of The Universe ◽  
The Universe ◽  
Insight Into

The main motivation to write this article is to relate the cosmology and topology in order to gain some insight into the topological signatures of the Standard model of Universe. The theory of General Relativity as given by Einstein only describes the local geometry of space but not global, hence leaves the possibility to explore the topology of the space (simply- or multi-connected). By expressing the cosmological model in trms of energy density parameters, we attempt to understand the geometry of spacetime. This is followed by a discussion on the possibility to detect the signatures of topology of space imprinted on the Cosmic Microwave Background (CMB).

scholarly journals Generalized Phenomenological Models of Dark Energy

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Prasenjit Paul ◽  
Rikpratik Sengupta
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Free Parameters ◽  
The Universe ◽  
Matter Energy

It was first observed at the end of the last century that the universe is presently accelerating. Ever since, there have been several attempts to explain this observation theoretically. There are two possible approaches. The more conventional one is to modify the matter part of the Einstein field equations, and the second one is to modify the geometry part. We shall consider two phenomenological models based on the former, more conventional approach within the context of general relativity. The phenomenological models in this paper consider a Λ term firstly a function of a¨/a and secondly a function of ρ, where a and ρ are the scale factor and matter energy density, respectively. Constraining the free parameters of the models with the latest observational data gives satisfactory values of parameters as considered by us initially. Without any field theoretic interpretation, we explain the recent observations with a dynamical cosmological constant.

The effect of sources on horizons that may develop when plane gravitational waves collide

1987 ◽  
Vol 414 (1846) ◽  
pp. 1-30 ◽  
Keyword(s):  
General Relativity ◽  
Electromagnetic Field ◽  
Energy Density ◽  
Special Relativity ◽  
Gravitational Waves ◽  
Perfect Fluid ◽  
Three Dimensional ◽  
Subsequent Time ◽  
Colliding Gravitational Waves ◽  
Plane Gravitational Waves

Colliding plane gravitational waves that lead to the development of a horizon and a subsequent time-like singularity are coupled with an electromagnetic field, a perfect fluid (whose energy density, ∊ , equals the pressure, p ), and null dust (consisting of massless particles). The coupling of the gravitational waves with an electromagnetic field does not affect, in any essential way, the development of the horizon or the time-like singularity if the polarizations of the colliding gravitational waves are not parallel. If the polarizations are parallel, the space-like singularity which occurs in the vacuum is transformed into a horizon followed by a three-dimensional time-like singularity by the merest presence of the electromagnetic field. The coupling of the gravitational waves with an ( ∊ = p )-fluid and null dust affect the development of horizons and singularities in radically different ways: the ( ∊ = p )-fluid affects the development decisively in all cases but qualitatively in the same way, while null dust prevents the development of horizons and allows only the development of space-like singularities. The contrasting behaviours of an ( ∊ = p )-fluid and of null dust in the framework of general relativity is compared with the behaviours one may expect, under similar circumstances, in the framework of special relativity.

scholarly journals dS/CFT at uniform energy density and a de Sitter “bluewall”

2014 ◽  
Vol 2014 (4) ◽  
Author(s):  
Diptarka Das ◽  
Sumit R. Das ◽  
K. Narayan
Keyword(s):  
Energy Density ◽  
De Sitter ◽  
Uniform Energy Density

scholarly journals CAN THE EXISTENCE OF DARK ENERGY BE DIRECTLY DETECTED?

2009 ◽  
Vol 24 (18n19) ◽  
pp. 3426-3436 ◽  
Author(s):  
MARTIN L. PERL
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Total Mass ◽  
Mass Density ◽  
Mass Energy ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
Expansion Of The Universe ◽  
The Universe

Over the last decade, astronomical observations show that the acceleration of the expansion of the universe is greater than expected from our understanding of conventional general relativity, the mass density of the visible universe, the size of the visible universe and other astronomical measurements. The additional expansion has been attributed to a variety of phenomenon that have been given the general name of dark energy. Dark energy in the universe seems to comprise a majority of the energy in the visible universe amounting to about three times the total mass energy. But locally the dark energy density is very small. However it is not zero. In this paper I describe the work of others and myself on the question of whether dark energy density can be directly detected. This is a work-in-progress and I have no answer at present.

scholarly journals Space-Time Curvature Of General Relativity And Energy Density Of A Three-Dimensional Quantum Vacuu

2015 ◽  
Vol 69 (1) ◽  
Author(s):  
Davide Fiscaletti ◽  
Amrit Sorli
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Vacuum Energy ◽  
Three Dimensional ◽  
Space Time ◽  
Vacuum Energy Density ◽  
Quantum Vacuum ◽  
Vacuum Condensate ◽  
Interesting Solution ◽  
Variable Energy

AbstractA three-dimensional quantum vacuum condensate is introduced as a fundamental medium from which gravity emerges in a geometro-hydrodynamic limit. In this approach, the curvature of space-time characteristic of general relativity is obtained as a mathematical value of a more fundamental actual variable energy density of quantum vacuum which has a concrete physical meaning. The fluctuations of the quantum vacuum energy density suggest an interesting solution for the dark energy problem.

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