Dynamical variables and evolution of the universe

2017 ◽  
Vol 26 (04) ◽  
pp. 1750029 ◽  
Author(s):  
M. Zaeem-ul-Haq Bhatti ◽  
Z. Yousaf
Keyword(s):  
Dust Cloud ◽  
Charged Dust ◽  
Matter Distribution ◽  
Field Equations ◽  
Riemann Curvature Tensor ◽  
Dynamical Equations ◽  
Curvature Invariants ◽  
Imperfect Fluid ◽  
Text Model ◽  
The Universe

One of the striking feature of inhomogeneous matter distribution under the effects of fourth-order gravity and electromagnetic field have been discussed in this manuscript. We have considered a compact spherical celestial star undergoing expansion due to the presence of higher curvature invariants of [Formula: see text] gravity and imperfect fluid. We have explored the dynamical equations and field equations in [Formula: see text] gravity. An explicit expression have been found for Weyl tensor and material variables under the dark dynamical effects. Using a viable [Formula: see text] model, some dynamical variables have been explored from splitting the Riemann curvature tensor. These dark dynamical variables are also studied for charged dust cloud with and without the constraint of constant Ricci scalar.

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.

Massive and massless scalar field models for Kaluza–Klein universe in f(R, T) gravity

2019 ◽  
Vol 34 (11) ◽  
pp. 1950066 ◽  
Author(s):  
Can Aktaş
Keyword(s):  
Scalar Field ◽  
Cosmological Term ◽  
Relativity Theory ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Field Equations ◽  
General Relativity Theory ◽  
Text Model ◽  
The Universe ◽  
Kaluza Klein

In this research, we have investigated the behavior of massive and massless scalar field (SF) models (normal and phantom) for Kaluza–Klein universe in [Formula: see text] gravity with cosmological term ([Formula: see text]). To obtain field equations, we have used [Formula: see text] model given by Harko et al. [Phys. Rev. D 84, 024020 (2011)] and anisotropy feature of the universe. Finally, we have discussed our results in [Formula: see text] and General Relativity Theory (GRT) with various graphics.

HOMOGENEOUS ANISOTROPIC COSMOLOGICAL MODELS WITH VISCOUS FLUID AND HEAT FLOW IN LYRA'S GEOMETRY

2009 ◽  
Vol 24 (23) ◽  
pp. 1847-1856 ◽  
Author(s):  
SHRI RAM ◽  
M. K. VERMA ◽  
MOHD ZEYAUDDIN
Keyword(s):  
Power Law ◽  
Bianchi Type ◽  
Big Bang ◽  
Field Equations ◽  
Type Singularity ◽  
Exponential Expansion ◽  
Imperfect Fluid ◽  
Lyra’S Geometry ◽  
Type V ◽  
The Universe

In this paper, a spatially homogeneous and anisotropic Bianchi type V model filled with an imperfect fluid with both viscosity and heat conduction is investigated within the framework of Lyra's geometry. Exact solutions of the field equations are obtained by applying a special law of variation for Hubble's parameter which yields a constant value of the deceleration parameter. Two different physically viable models of the universe are presented in two types of cosmologies, one with power-law expansion and other one with exponential expansion. Cosmological model with power-law expansion has an initial big-bang type singularity at t = 0 whereas the model with exponential expansion has a singularity in the infinite past. The physical and dynamical properties of the models are discussed.

Gravitational collapse and dark universe with LTB geometry

2016 ◽  
Vol 26 (06) ◽  
pp. 1750045 ◽  
Author(s):  
M. Zaeem-ul-Haq Bhatti ◽  
Z. Yousaf
Keyword(s):  
Black Hole ◽  
Electromagnetic Field ◽  
Time Interval ◽  
Curvature Scalar ◽  
Field Equations ◽  
Dark Sector ◽  
Curvature Invariants ◽  
Text Model ◽  
Polynomial Formula ◽  
Electrically Charged

The objective of this paper is to examine the influence of polynomial [Formula: see text] dark sector cosmic terms on the collapse of electrically charged Lemaître–Tolman–Bondi geometry. We explored a class of solutions for [Formula: see text] field equations in the existence of electromagnetic field and under the constraint of constant curvature scalar. The influence of [Formula: see text] model on the dynamics of collapsing object have been discussed by studying its black hole and cosmological horizons. Also, the effects of these dark sources on the time interval between the corresponding singularities and horizons have been studied. We investigated that the process of collapse slows down due to the higher order curvature invariants of polynomial [Formula: see text] model and electromagnetic field.

CONSTRAINTS OF INITIAL DATA FOR A DISCRETE UNIVERSE

2012 ◽  
Vol 12 ◽  
pp. 213-223
Author(s):  
KJELL ROSQUIST ◽  
LARS SAMUELSSON
Keyword(s):  
Initial Data ◽  
Clusters Of Galaxies ◽  
Einstein Field Equations ◽  
Matter Distribution ◽  
Field Equations ◽  
And Topology ◽  
Discrete Nature ◽  
The Universe

The matter distribution of the universe is observed to be discrete in the form of stars, galaxies and clusters of galaxies. Due to the non-linearities of the Einstein field equations, the discrete nature of the matter implies modifications of the standard Friedmann cosmology paradigm. The modifications affect both the dynamics and the possible cosmological initial data. We discuss properties and restrictions for the intial data of a universe with a discrete matter distribution, in particular possible implications for the curvature and topology.

scholarly journals Vacuum dynamics in the Universe versus a rigid Λ=const.

2017 ◽  
Vol 32 (19n20) ◽  
pp. 1730014 ◽  
Author(s):  
Joan Solà ◽  
Adrià Gómez-Valent ◽  
Javier de Cruz Pérez
Keyword(s):  
Fundamental Constant ◽  
Dynamical Variable ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Cosmological Observations ◽  
Local Measurements ◽  
Power Law Function ◽  
Text Model ◽  
Bayesian Criteria ◽  
The Universe

In this year, in which we celebrate 100 years of the cosmological term, [Formula: see text], in Einstein’s gravitational field equations, we are still facing the crucial question whether [Formula: see text] is truly a fundamental constant or a mildly evolving dynamical variable. After many theoretical attempts to understand the meaning of [Formula: see text], and in view of the enhanced accuracy of the cosmological observations, it seems now mandatory that this issue should be first settled empirically before further theoretical speculations on its ultimate nature. In this review, we summarize the situation of some of these studies. Devoted analyses made recently show that the [Formula: see text] hypothesis, despite being the simplest, may well not be the most favored one. The overall fit to the cosmological observables SNIa[Formula: see text]+[Formula: see text]BAO[Formula: see text]+H(z)[Formula: see text]+[Formula: see text]LSS[Formula: see text]+[Formula: see text]BBN[Formula: see text]+[Formula: see text]CMB single out the class of “running” vacuum models (RVMs), in which [Formula: see text] is an affine power-law function of the Hubble rate. It turns out that the performance of the RVM as compared to the “concordance” [Formula: see text] model (with [Formula: see text]) is much better. The evidence in support of the RVM may reach [Formula: see text] c.l., and is bolstered with Akaike and Bayesian criteria providing strong evidence in favor of the RVM option. We also address the implications of this framework on the tension between the CMB and local measurements of the current Hubble parameter.

scholarly journals Axially Symmetric Bulk Viscous String Cosmological Models in GR and Brans-Dicke Theory of Gravitation

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
V. U. M. Rao ◽  
D. Neelima
Keyword(s):  
General Relativity ◽  
Bulk Viscosity ◽  
Space Time ◽  
Cosmological Models ◽  
Axially Symmetric ◽  
Matter Distribution ◽  
Field Equations ◽  
Theory Of Gravitation ◽  
The Universe ◽  
Special Case

Axially symmetric string cosmological models with bulk viscosity in Brans-Dicke (1961) and general relativity (GR) have been studied. The field equations have been solved by using the anisotropy feature of the universe in the axially symmetric space-time. Some important features of the models, thus obtained, have been discussed. We noticed that the presence of scalar field does not affect the geometry of the space-time but changes the matter distribution, and as a special case, it is always possible to obtain axially symmetric string cosmological model with bulk viscosity in general relativity.

scholarly journals Evolution of inhomogeneous LTB geometry with tilted congruence and modified gravity

2017 ◽  
Vol 95 (12) ◽  
pp. 1246-1252 ◽  
Author(s):  
Z. Yousaf ◽  
M. Zaeem-ul-Haq Bhatti ◽  
Aamna Rafaqat
Keyword(s):  
Transport Equation ◽  
Modified Gravity ◽  
Stability Region ◽  
Moving Frames ◽  
Field Equations ◽  
Dynamical Equations ◽  
Inhomogeneous Universe ◽  
The Stability ◽  
The Relationship ◽  
The Universe

The goal of this paper is to shed some light on the significance of congruence of observers, which seems to affect the dynamics of the universe under Palatini f(R) formalism. Starting by setting up the formalism needed, we have explored the field equations using Lemaitre–Tolman–Bondi geometry as an interior metric. We have formulated the relationship between the matter variables as seen by the observers in both co-moving and non-co-moving frames. The dynamical equations are evaluated to study the dynamics of inhomogeneous universe by exploring conservation equations along with the Ellis equations. We have also explored a collapsing factor describing the bouncing phenomena via transport equation and conclude the stability region.

scholarly journals Surface tension: Accelerated expansion, coincidence problem & Hubble tension

2020 ◽  
pp. 2050115
Author(s):  
C. Ortiz
Keyword(s):  
Hubble Constant ◽  
Conservation Equation ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Coincidence Problem ◽  
Dynamical Equations ◽  
Energy Conservation Equation ◽  
Expansion Of The Universe ◽  
General Relativistic ◽  
The Universe

In this paper, we give a physical explanation to the accelerated expansion of the universe, alleviating the tension between the discrepancy of Hubble constant measurements. By the EulerCauchy stress principle, we identify a controversy on the lack of consideration of the surface forces contemplated in the study of the expansion of the universe. We distinguish a new general relativistic effect that modifies the spacetime fabric by means of the energy conservation equation. The resulting dynamical equations from the proposed hypothesis are contrasted to several testable astrophysical predictions. This paper also explains why we have not found any particle or fluid responsible for dark energy and clarifies the Cosmological Coincidence Problem. These explanations are achieved without assuming the existence of exotic matter of unphysical meaning or having to modify Einstein’s Field Equations.

Instability analysis of expansion-free sphere in f(𝒢) gravity

2017 ◽  
Vol 26 (09) ◽  
pp. 1750104
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Dynamical Instability ◽  
Anisotropic Fluid ◽  
Free Fluid ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
First Order ◽  
Text Model ◽  
Metric Functions ◽  
Anisotropic Pressures

The aim of this paper is to study the dynamical instability of expansion-free spherically symmetric anisotropic fluid in the framework of [Formula: see text] gravity. We apply perturbation scheme of the first-order to the metric functions as well as matter variables and construct modified field equations for both static and perturbed configurations using power-law [Formula: see text] model. To discuss the instability dynamics, we use the contracted Bianchi identities to formulate the dynamical equations in both Newtonian and post-Newtonian regimes. It is found that the range of instability is independent of adiabatic index for expansion-free fluid but depends on anisotropic pressures, energy density and Gauss–Bonnet (GB) terms.

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