Measure of complexity for dynamical self-gravitating structures

2020 ◽  
Vol 29 (09) ◽  
pp. 2050061
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti ◽  
T. Naseer
Keyword(s):  
Modified Gravity ◽  
Heat Dissipation ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Fluid Distribution ◽  
Source Terms ◽  
Matter Distribution ◽  
Structure Scalars ◽  
Definition Of ◽  
Modified Theory

We consider the definition of complexity for dynamical spherically self-gravitating matter distribution in the presence of heat dissipation introduced by Herrera [L. Herrera, A. Di Prisco and J. Ospino, Phys. Rev. D 98 (2018) 104059] and generalize it in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are the Ricci scalar and the trace of energy–momentum tensor, respectively. We measure the complexity of structure as well as pattern of evolution of the fluid distribution and examine these under the effects of dark source terms of modified gravity. Some dynamical and kinematical equations are observed in the dissipative and nondissipative cases in the background of modified theory. Finally, we discuss evolution of the structure scalars and stability of a condition where the complexity factor vanishes.

scholarly journals Influence of modification of gravity on the complexity factor of static spherical structures

2020 ◽  
Vol 495 (4) ◽  
pp. 4334-4346
Author(s):  
Z Yousaf ◽  
Maxim Yu Khlopov ◽  
M Z Bhatti ◽  
T Naseer
Keyword(s):  
Gravitational Theory ◽  
Momentum Tensor ◽  
Matter Distribution ◽  
Field Equations ◽  
Riemann Curvature Tensor ◽  
Structure Scalars ◽  
Pressure Anisotropy ◽  
Spherical Structures ◽  
Energy Density Inhomogeneity ◽  
Definition Of

ABSTRACT The aim of this paper is to generalize the definition of complexity for the static self-gravitating structure in f (R, T, Q) gravitational theory, where R is the Ricci scalar, T is the trace part of energy–momentum tensor, and Q ≡ RαβT αβ. In this context, we have considered locally anisotropic spherical matter distribution and calculated field equations and conservation laws. After the orthogonal splitting of the Riemann curvature tensor, we found the corresponding complexity factor with the help of structure scalars. It is seen that the system may have zero complexity factor if the effects of energy density inhomogeneity and pressure anisotropy cancel the effects of each other. All of our results reduce to general relativity on assuming f (R, T, Q) = R condition.

scholarly journals Cosmological models with squared trace in modified gravity

2020 ◽  
Vol 29 (15) ◽  
pp. 2050100
Author(s):  
B. Mishra ◽  
S. K. Tripathy ◽  
Saibal Ray
Keyword(s):  
Modified Gravity ◽  
Hubble Parameter ◽  
Energy Momentum Tensor ◽  
Cosmological Parameters ◽  
Momentum Tensor ◽  
Scale Factor ◽  
Specific Form ◽  
Cosmological Models ◽  
Modified Theory Of Gravity ◽  
Modified Theory

In this work, we present a few simple cosmological models under the modified theory of gravity in the particular form of [Formula: see text], where [Formula: see text] is the Ricci Scalar and [Formula: see text] is the trace of the energy–momentum tensor. Two special cosmological models are studied with (i) hyperbolic scale factor and (ii) specific form of the Hubble parameter. The models are observed to predict relevant cosmological parameters closer to the observational values. Both the models reduce to overlap with the [Formula: see text]CDM model at late times. We have discussed some interesting results related to wormhole solutions as evolved from our model. The possible occurrence of Big Trip in wormholes for the models are also discussed.

Spherically symmetric traversable wormholes in f(R2,T) gravity

2019 ◽  
Vol 16 (10) ◽  
pp. 1950147 ◽  
Author(s):  
M. Zubair ◽  
Quratulien Muneer ◽  
Saira Waheed
Keyword(s):  
Modified Gravity ◽  
Arbitrary Constant ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Field Equations ◽  
Traversable Wormholes

In this paper, we explore the possibility of wormhole solutions existence exhibiting spherical symmetry in an interesting modified gravity based on Ricci scalar term and trace of energy–momentum tensor. For this reason, we assume the matter distribution as anisotropic fluid and a specific viable form of the generic function given by [Formula: see text] involving [Formula: see text] and [Formula: see text], two arbitrary constant parameters. For having a simplified form of the resulting field equations, we assume three different forms of EoS of the assumed matter contents. In each case, we find the numerical wormhole solutions and analyze their properties for the wormhole existence graphically. The graphical behavior of the energy condition bounds is also investigated in each case. It is found that a realistic wormhole solutions satisfying all the properties can be obtained in each case.

Impact of f(R,T) gravity in evolution of charged viscous fluids

2021 ◽  
Vol 30 (04) ◽  
pp. 2150027
Author(s):  
I. Noureen ◽  
Usman-ul-Haq ◽  
S. A. Mardan
Keyword(s):  
Stability Analysis ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Viscous Fluids ◽  
Fluid Distribution ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stability Of Stars ◽  
The Stability

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of [Formula: see text] gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

Charged gravastars in f(R,T,RμνTμν) gravity

2021 ◽  
pp. 2150084
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti
Keyword(s):  
Perfect Fluid ◽  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Mathematical Formulation ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
De Sitter ◽  
The Stability ◽  
Physical Features ◽  
Modified Theory

We explore the aspects of the electromagnetism on the stability of gravastar in a particular modified theory, i.e. [Formula: see text] where [Formula: see text], [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. We assume a spherically symmetric static metric coupled comprising of perfect fluid in the presence of electric charge. The purpose of this paper is to extend the results of [S. Ghosh, F. Rahaman, B. K. Guha and S. Ray, Phys. Lett. B 767 (2017) 380.] to highlight the effects of [Formula: see text] gravity in the formation of charged gravastars. We demonstrated the mathematical formulation, utilizing different equations of state, for the three respective regions (i.e. inner, shell, exterior) of the gravastar. We have matched smoothly the interior de Sitter and the exterior Reissner–Nordström metric at the hypersurface. At the end we extracted few conclusions by working on the physical features of the charged gravastar, mathematically and graphically.

scholarly journals On homogeneous and isotropic universe

2015 ◽  
Vol 30 (34) ◽  
pp. 1550186 ◽  
Author(s):  
M. O. Katanaev
Keyword(s):  
Vector Fields ◽  
Energy Momentum Tensor ◽  
Killing Vector ◽  
Momentum Tensor ◽  
Killing Vector Fields ◽  
Full System ◽  
Independent Functions ◽  
Definition Of ◽  
Usual Scale ◽  
Matter Energy

We give a simple example of spacetime metric, illustrating that homogeneity and isotropy of space slices at all moments of time is not obligatory lifted to a full system of six Killing vector fields in spacetime, thus it cannot be interpreted as a symmetry of a four-dimensional metric. The metric depends on two arbitrary and independent functions of time. One of these functions is the usual scale factor. The second function cannot be removed by coordinate transformations. We prove that it must be equal to zero, if the metric satisfies Einstein’s equations and the matter energy–momentum tensor is homogeneous and isotropic. A new, equivalent, definition of homogeneous and isotropic spacetime is given.

Various dark energy models for variables G and Λ in f(R, T) modified theory

2019 ◽  
Vol 34 (13) ◽  
pp. 1950098 ◽  
Author(s):  
Can Aktaş
Keyword(s):  
Dark Energy ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Tachyon Field ◽  
Field Equations ◽  
Frw Universe ◽  
Linearly Varying Deceleration Parameter ◽  
Energy Models ◽  
Modified Theory ◽  
Friedmann Robertson Walker

In this paper, we have researched tachyon field, k-essence and quintessence dark energy (DE) models for Friedmann–Robertson–Walker (FRW) universe with varying G and [Formula: see text] in f(R, T) gravitation theory. The theory of f(R, T) is proposed by Harko et al. [Phys. Rev. D 84, 024020, 2011]. In this theory, R is the Ricci scalar and T is the trace of energy–momentum tensor. For the solutions of field equations, we have used linearly varying deceleration parameter (LVDP), the equation of state (EoS) and the ratio between [Formula: see text] and Hubble parameter. Also, we have discussed some physical behavior of the models with various graphics.

scholarly journals Gravitational energy in the framework of embedding and splitting theories

2018 ◽  
Vol 27 (02) ◽  
pp. 1750188 ◽  
Author(s):  
D. A. Grad ◽  
R. V. Ilin ◽  
S. A. Paston ◽  
A. A. Sheykin
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Gravitational Energy ◽  
Einstein Equations ◽  
Field Energy ◽  
Energy Localization ◽  
Embedding Theory ◽  
Isometric Embeddings ◽  
Definition Of ◽  
Noether Current

We study various definitions of the gravitational field energy based on the usage of isometric embeddings in the Regge–Teitelboim approach. For the embedding theory, we consider the coordinate translations on the surface as well as the coordinate translations in the flat bulk. In the latter case, the independent definition of gravitational energy–momentum tensor appears as a Noether current corresponding to global inner symmetry. In the field-theoretic form of this approach (splitting theory), we consider Noether procedure and the alternative method of energy–momentum tensor defining by varying the action of the theory with respect to flat bulk metric. As a result, we obtain energy definition in field-theoretic form of embedding theory which, among the other features, gives a nontrivial result for the solutions of embedding theory which are also solutions of Einstein equations. The question of energy localization is also discussed.

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