scholarly journals Energy Definition and Dark Energy: A Thermodynamic Analysis

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
H. Moradpour ◽  
J. P. Morais Graça ◽  
I. P. Lobo ◽  
I. G. Salako
Keyword(s):  
Conservation Law ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Accelerated Expansion ◽  
Expansion Phase ◽  
Definition Of ◽  
Relaxed Energy ◽  
Thermodynamic Pressure ◽  
The Universe ◽  
Energy Momentum Conservation

Accepting the Komar mass definition of a source with energy-momentum tensor Tμν and using the thermodynamic pressure definition, we find a relaxed energy-momentum conservation law. Thereinafter, we study some cosmological consequences of the obtained energy-momentum conservation law. It has been found out that the dark sectors of cosmos are unifiable into one cosmic fluid in our setup. While this cosmic fluid impels the universe to enter an accelerated expansion phase, it may even show a baryonic behavior by itself during the cosmos evolution. Indeed, in this manner, while Tμν behaves baryonically, a part of it, namely, Tμν(e) which is satisfying the ordinary energy-momentum conservation law, is responsible for the current accelerated expansion.

FRW universe in f(R,T) gravity

2021 ◽  
pp. 2150104
Author(s):  
R. K. Tiwari ◽  
D. Sofuoğlu ◽  
A. Beesham
Keyword(s):  
Phase Transition ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Field Equations ◽  
Frw Universe ◽  
Expansion Phase ◽  
Age Of The Universe ◽  
The Universe ◽  
Modified Theory ◽  
Friedmann Robertson Walker

In this study, Friedmann–Robertson–Walker space-time filled with a perfect fluid in [Formula: see text] modified theory, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the energy–momentum tensor of matter, has been considered. The investigation of the phase transition of the universe from the decelerating expansion phase to the accelerating one has been made by adopting a special form of the varying deceleration parameter that is inversely proportional to the Hubble parameter. The exact solution of the field equations has been derived. The kinematic and dynamical quantities of the model have been obtained and their evolutions have been discussed by means of their graphs. The statefinder diagnostic has been used and the age of the universe has been computed for testing the validity of the model. It has been shown that the dominant energy of the model is ordinary matter which behaves as the SCDM model at the beginning and it is a quintessence like fluid which behaves as the [Formula: see text]CDM model at late times.

scholarly journals Proposal for the proper gravitational energy–momentum tensor

2016 ◽  
Vol 31 (26) ◽  
pp. 1650151 ◽  
Author(s):  
Katsutaro Shimizu
Keyword(s):  
Black Hole ◽  
Energy Momentum Tensor ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Gravitational Energy ◽  
Coordinate Transformations ◽  
Black Hole Mass ◽  
Schwarzschild Black Hole ◽  
Flrw Universe ◽  
Energy Momentum Conservation

We propose a gravitational energy–momentum (GEMT) tensor of the general relativity obtained using Noether’s theorem. It transforms as a tensor under general coordinate transformations. One of the two indices of the GEMT labels a local Lorentz frame that satisfies the energy–momentum conservation law. The energies for a gravitational wave, a Schwarzschild black hole and a Friedmann–Lemaitre–Robertson–Walker (FLRW) universe are calculated as examples. The gravitational energy of the Schwarzschild black hole exists only outside the horizon, its value being the negative of the black hole mass.

Viscous effects in the dark sector of the Universe

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040041
Author(s):  
J. C. Fabris ◽  
T. R. P. Caramês ◽  
A. Wojnar ◽  
H. E. S. Velten
Keyword(s):  
Short Review ◽  
Point Of View ◽  
Accelerated Expansion ◽  
Viscous Effects ◽  
Dark Sector ◽  
Expansion Phase ◽  
Observational Point ◽  
Small Scales ◽  
Viscous Models ◽  
The Universe

Viscous properties are attributed to the dark sector of the Universe. They contribute to the accelerated expansion phase of the Universe and can alleviate existing tensions in the [Formula: see text]CDM model at small scales. We provide a short review of recent efforts on this topic. Different viscous models for the dark sector are analysed both from theoretical and observational point of view.

scholarly journals DISCRETE SYMMETRIES AND GENERAL RELATIVITY, THE DARK SIDE OF GRAVITY

2005 ◽  
Vol 20 (11) ◽  
pp. 2341-2345 ◽  
Author(s):  
FREDERIC HENRY-COUANNIER
Keyword(s):  
General Relativity ◽  
Discrete Symmetries ◽  
Blue Shift ◽  
Accelerated Expansion ◽  
Dark Side ◽  
Galactic Rotation ◽  
Expansion Phase ◽  
Coordinate Singularity ◽  
General Relativistic ◽  
The Universe

The parity and time reversal invariant actions, equations and their conjugated metric solutions are obtained in the context of a general relativistic model modified in order to suitably take into account discrete symmetries. The equations are not covariant however the predictions of the model, in particular its Schwarzschild metric solution in vacuum, only start to differ from those of General Relativity at the Post-Post-Newtonian order. No coordinate singularity (black hole) arises in the privileged coordinate system where the energy of gravity is found to vanish. Vacuum energies have no gravitational effects. A flat universe accelerated expansion phase is obtained without resorting to inflation nor a cosmological constant. The context may be promising to help us elucidate several outstanding enigmas such as the Pioneer anomalous blue-shift, flat galactic rotation curves or the universe voids.

scholarly journals The origin of the energy–momentum conservation law

2017 ◽  
Vol 384 ◽  
pp. 85-104 ◽  
Author(s):  
Andrew E. Chubykalo ◽  
Augusto Espinoza ◽  
B.P. Kosyakov
Keyword(s):  
Conservation Law ◽  
Momentum Conservation ◽  
Energy Momentum Conservation

scholarly journals Construction of energy–momentum tensor of gravitation

2016 ◽  
Vol 13 (01) ◽  
pp. 1650001 ◽  
Author(s):  
Kazuharu Bamba ◽  
Katsutaro Shimizu
Keyword(s):  
General Relativity ◽  
Energy Momentum Tensor ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Gravitational Energy ◽  
Lorentz Frame ◽  
Noether Theorem ◽  
General Coordinate Transformation ◽  
Two Indices ◽  
Energy Momentum Conservation

We construct the gravitational energy–momentum tensor in general relativity through the Noether theorem. In particular, we explicitly demonstrate that the constructed quantity can vary as a tensor under the general coordinate transformation. Furthermore, we verify that the energy–momentum conservation is satisfied because one of the two indices of the energy–momentum tensor should be in the local Lorentz frame. It is also shown that the gravitational energy and the matter one cancel out in certain space-times.

scholarly journals Some Second-Order Tensor Calculus Identities and Applications in Continuum Mechanics

2018 ◽  
Author(s):  
Bohua Sun
Keyword(s):  
Continuum Mechanics ◽  
Conservation Law ◽  
Momentum Conservation ◽  
Second Order ◽  
Tensor Analysis ◽  
Tensor Calculus ◽  
Order Tensor ◽  
Definition Of

To extend the calculation power of tensor analysis, we introduce four new definition of tensor calculations. Some useful tensor identities have been proved. We demonstrate the application of the tensor identities in continuum mechanics: momentum conservation law and deformation superposition.

scholarly journals A periodic varying deceleration parameter in f(R, T) gravity

2018 ◽  
Vol 33 (33) ◽  
pp. 1850193 ◽  
Author(s):  
P. K. Sahoo ◽  
S. K. Tripathy ◽  
Parbati Sahoo
Keyword(s):  
Deceleration Parameter ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Oscillatory Behavior ◽  
Matter Content ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Field Equations ◽  
Eos Parameter ◽  
Wide Range

The phenomenon of accelerated expansion of the present universe and a cosmic transit aspect is explored in the framework of a modified gravity theory known as f(R, T) gravity (where R is the Ricci scalar and T is the trace of the energy–momentum tensor of the matter content). The cosmic transit phenomenon signifies a signature flipping behavior of the deceleration parameter. We employ a periodic varying deceleration parameter and obtained the exact solution of field equations. The dynamical features of the model including the oscillatory behavior of the EOS parameter are studied. We have also explored the obvious violation of energy–momentum conservation in f(R, T) gravity. The periodic behavior of energy conditions for the model are also discussed with a wide range of the free parameters.

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