arXiv subjects

M. Z. Bhatti

Publications and source records attributed to M. Z. Bhatti.

34 records · Page 2Linked to original sources

arXiv2021

Role of Structure Scalars on the evolution of Compact Objects in Palatini $f(R)$ Gravity

The utmost concern of this article is the construction of modified scalar functions (structure scalars) by taking Palatini $f(R)$ gravitational theory into account. At first, a general formalism is established in which we assess gravitational stellar equations by putting into use the Palatini's technique. Later, from the perspective of tilted observer, we Lorentz boosted the components of energy-momentum tensor using relative velocity $ω$. To examine the physical as well as mathematical aspects of the fluid source, we carry out a detailed analysis of kinematical variables by evaluating shear tensor and scalar, four-acceleration and expansion scalar. For the fluid content inside our spherical star, we inferred the mass function (geometric mass) and the active gravitational mass. Raychaudhuri equation, Bianchi identities in addition to few other equations are worked out to discern the structure formation and analyze the object's evolutionary stages. The Riemann tensor is then broken up orthogonally to set up few scalar functions connected with fundamental physical characteristics of the fluid source like energy density, effects of tidal forces and anisotropic stresses etc.

gr-qc↗

arXiv2020

Measure of Complexity in Self-Gravitating Systems using Structure Scalars

The aim of this paper is to present the definition of complexity for static self-gravitating anisotropic matter proposed in $f(G,T)$ theory, where $G$ is the Gauss-Bonnet term and $T$ is the trace of energy momentum tensor. We evaluate field equations, Tolman-Oppenheimer-Volkoff equation, mass functions and structure scalars. Among the calculated modified scalar variables that are obtained from the orthogonal splitting of Riemann tensor, a single scalar function has been identified as the complexity factor. After exploring the corresponding Tolmann mass function, it is seen that the complexity factor along with the $f(G,T)$ terms have greatly influenced its formulation and its role in the subsequent radial phases of the spherical system. We have also used couple of ansatz in order to discuss possible solutions of equations of motion in the study of the structure of compact object.

physics.gen-ph↗

arXiv2020

Influence of Modification of Gravity on the Complexity Factor of Static Spherical Structures

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 $Q\equiv R_{αβ}T^{αβ}$. 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.

gr-qc↗

arXiv2020

Dynamical Analysis of Self-gravitating Stars in Modified Gauss-Bonnet Gravity

In this paper, we have continued the work of Herrera \emph{et al.} \cite{herrera2012dynamical} in $f(G)$ gravitational theory. For this purpose, a spherically symmetric fluid exhibiting locally anisotropic pressure along with the energy density, is taken under consideration. The perturbation scheme is imposed on modified field equations and the dynamical equations. The collapse equation is devised from these perturbed equations which stimulates to disclose the instability zone under both Newtonian and post-Newtonian constraints. It is wrapped up by concluding that dynamical instability is interpreted by the adiabatic index $Γ$ which relies on the anisotropic pressure, energy density and the dark source terms due to $f(G)$ gravity.

gr-qc↗

arXiv2020

The Measure of Complexity in Charged Celestial Bodies in $f(R,T,R_{μν}T^{μν})$ Gravity

In this paper, we investigate irregularities in a cylindrical self-gravitating system which contains the properties of an imperfect matter and electromagnetic field. For $f(R,T,Q)$ theory, in which $R$ represents the Ricci scalar and $T$ shows the trace of matter stress-energy tensor while $Q\equiv R_{γδ}T^{γδ}$, the field equations containing electric charge, mass functions and Darmois junction conditions at the hypersurface are examined. We have adopted new definition of complexity introduced by Herrera \cite{herrera2018new}, generalized it for the static charged cylindrically symmetric case in $f(R,T,Q)$ theory by performing a detailed analysis on the orthogonal splitting of the Riemann curvature tensor. One of the effective scalars, $Y_{TF}$, has been recognized as a complexity factor. This factor is comprised of certain physical components of the fluid such as irregularity in energy density, locally pressure anisotropy and electric charge (arranged in a specific way). In addition, the effects of extra curvature terms of modified gravity are examined by making the relations among the complexity factor, Weyl scalar and Tolman mass.

physics.gen-ph↗

arXiv2020

Gravastars in $f(R,G)$ Gravity

In this paper, we discuss some feasible features of gravastar that were firstly demonstrated by Mazur and Mottola. It is already established that gravastar associates the de-Sitter spacetime in its inner sector with the Schwarzschild geometry at its exterior through the thin shell possessing the ultra-relativistic matter. We have explored the singularity free spherical model with a particular equation of state under the influence of $f(R,G)$ gravity, where $R$ is the Ricci scalar and $G$ is the Gauss-Bonnet term. The interior geometry is matched with a suitable exterior using Israel formalism. Also, we discussed a feasible solution of gravastar which describes the other physically sustainable factors under the influence of $f(R,G)$ gravity. Different realistic characteristics of the gravastar model are discussed, in particular, shell's length, entropy, and energy. A significant role of this particular gravity is examined for the sustainability of gravastar model.

gr-qc↗

arXiv2020

New Definition of Complexity Factor in $f(R,T,R_{μν}T^{μν})$ Gravity

This paper is devoted to present new definition of complexity factor for static cylindrically symmetric matter configurations in $f(R,T,R_{μν}T^{μν})$ gravity. For this purpose, we have considered irrotational static cylindrical spacetime coupled with a locally anisotropic relativistic fluid. After formulating gravitational field and conservation equations, we have performed orthogonal splitting of the Riemann curvature tensor. Unlike GR (for spherical case) the one of the structure scalars $X_{TF}$, has been identified to be a complexity factor. This factor contains effective forms of the energy density, and anisotropic pressure components. Few peculiar relations among complexity factor, Tolman mass and Weyl scalar are also analyzed with the modified $f(R,T,R_{μν}T^{μν})$ corrections.

gr-qc↗

arXiv2020

Gravastars in $f(R,T,R_{μν}T^{μν})$ Gravity

This work is devoted to study the analytical and regular solutions of a particular self-gravitating object (i.e., gravastar) in a particular theory of gravity. We derive the corresponding field equations in the presence of effective energy momentum tensor associated with the perfect fluid configuration of a spherical system. We then describe the mathematical formulations of the three respective regions i.e., inner, shell and exterior of a gravastar separately. Additionally, the significance and physical characteristics along with the graphical representation of gravastars are discussed in detail. It is seen that under some specific constraints, $f(R,T,R_{μν}T^{μν})$ gravity is likely to host gravastars.

gr-qc↗

arXiv2019

Charged Gravastars in Modified Gravity

In this paper, we investigate the effects of electromagnetic field on the isotropic spherical gravastar models in metric $f(R,T)$ gravity. For this purpose, we have explored singularity-free exact models of relativistic spheres with a specific equation of state. After considering Reissner Nordström spacetime as an exterior region, the interior charged manifold is matched at the junction interface. Several viable realistic characteristics of the spherical gravastar model are studied in the presence of electromagnetic field through graphical representations. It is concluded that the electric charge has a substantial role in the modeling of proper length, energy contents, entropy and equation of state parameter of the stellar system. We have also explored the stable regions of the charged gravastar structures.

gr-qc↗

arXiv2019

Dissipative Self-Gravitating Systems in Modified Gravity

We discuss the gravitational collapse of spherical compact objects in the background of $f(R,T,Q)$ theory, where $R$ represent the Ricci scalar, $T$ is the trace of energy momentum tensor while $Q\equiv R_{μν}T^{μν}$, and investigate the influence of anisotropy and heat dissipation in this scenario. We provide an analysis on the role of distinct material terms considered while studying the dynamical equation. The dynamical equation is coupled with a heat transport equation and discussed in the background of $f(R,T,Q)$ theory of gravity. The reduction element in the density of inertial mass, is re-acquired which is based on the internal position of thermodynamics. In collation with the equivalence relation, the reduction quantity in density is similar as appeared with gravitational force. We formulate the connection of Weyl tensor with different matter variables to see the non-identical outcomes. The inhomogeneous nature of energy density is also analyzed in the framework of modified gravity.

gr-qc↗

arXiv2019

Bounds on Higher Derivative $f(R,\square R,T)$ Models from Energy Conditions

This paper studies the viable regions of some cosmic models in a higher derivative $f(R,\square R, T)$ theory with the help of energy conditions (where $R$ and $T$ are the Ricci scalar, 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 $f(R,\square R, T)$ models are examined.

gr-qc↗

arXiv2018

Dynamical Instability of Spherical Anisotropic Sources in $f(R,T,R_{μν}T^{μν})$ Gravity

In this paper, we study the effects of modification of gravity on the problem of dynamical instability of the spherical relativistic anisotropic interiors. We have considered non-zero influence of expansion scalar throughout during the evolutionary phases of spherical geometry that led to the use of fluid stiffness parameter. The modified hydrostatic equation for the stellar anisotropic matter distributions is constructed and then solved by using radial perturbation scheme. Such a differential equation can be further used to obtain instability constraints at both weak field and post-Newtonian approximations after considering a particular Harrison-Wheeler equation of state. This approach allows us to deal with the effects of usual and effective matter variables on the stability exotic stellar of self-gravitating structures.

gr-qc↗

arXiv2018

Energy Conditions in Higher Derivative $f(R,\Box R,T)$ Gravity

In this paper, we examined the viability bounds of a higher derivative $f(R,\Box R, T)$ theory through analyzing energy conditions (where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor, respectively). We take flat Friedmann-Lemaître-Robertson-Walker spacetime coupled with ideal configurations of matter content. We consider three different realistic models of this gravity, that could be utilized to understand the stability of cosmological solutions. After constructing certain bounds mediated by energy conditions, more specifically weak energy condition, we discuss viable zones of the under considered modified models in an environment of recent estimated numerical choices of the cosmic parameters.

gr-qc↗

arXiv2017

Influence of $f(R)$ Models on the Existence of Anisotropic Self-Gravitating Systems

This paper aims to explore some realistic configurations of anisotropic spherical structures in the background of metric $f(R)$ gravity, where $R$ is the Ricci scalar. The solutions obtained by Krori and Barua are used to examine the nature of particular compact stars with three different modified gravity models. The behavior of material variables is analyzed through plots and the physical viability of compact stars is investigated through energy conditions. We also discuss the behavior of different forces, equation of state parameter, measure of anisotropy and Tolman-Oppenheimer-Volkoff equation in the modeling of stellar structures. The comparison from our graphical representations may provide evidences for the realistic and viable $f(R)$ gravity models at both theoretical and astrophysical scale.

gr-qc↗

arXiv2017

Evolution of Compact Stars and Dark Dynamical Variables

This work is aimed to explore the dark dynamical effects of $f(R,T)$ modified gravity theory on the dynamics of compact celestial star. We have taken the interior geometry as spherical star which is filled with imperfect fluid distribution. The modified field equations are explored by taking a particular form of $f(R,T)$ model, i.e., $f(R,T)=f_1(R)+f_2(R)f_3(T)$. These equations are then utilized to formulate the well-known structure scalars under the dark dynamical effects of this higher order gravity theory. Also, the evolution equations for expansion and shear are formulated with the help of these scalar variables. Further, all this analysis have been made under the condition of constant $R$ and $T$. We found a crucial significance of dark source terms and dynamical variables on the evolution and density inhomogeneity of compact objects.

gr-qc↗

arXiv2017

Energy Conditions in Modified $f(G)$ Gravity

In this paper, we have considered flat Friedmann-Lemaître-Robertson-Walker metric in the framework of perfect fluid models and modified $f(G)$ gravity (where $G$ is the Gauss Bonnet invariant). Particularly, we have considered particular realistic $f(G)$ configurations that could be used to cure finite-time future singularities arising in the late-time cosmic accelerating epochs. We have then developed the viability bounds of these models induced by weak and null energy conditions, by using the recent estimated numerical figures of the deceleration, Hubble, snap and jerk parameters.

gr-qc↗