Trace Of Stress-energy Tensor Research Articles

Thin-shell wormholes with electromagnetic effects in f(R,T) gravity

The purpose of this paper is to study the feasibility and the appearance of charged thin-shell wormholes using generalized Chaplygin gas under the influence of minimally coupled [Formula: see text] gravitational theory. Here, [Formula: see text] is a generic function of the scalar curvature [Formula: see text] and the trace of stress-energy tensor [Formula: see text]. We explore different components of Lanczos equations in the context of a specific [Formula: see text] functional form, i.e. [Formula: see text], by applying junction conditions on field equations. We study static stable solutions using radial perturbation and the generalized Chaplygin gas equation of state (EoS) with the isotropic environment. We investigate the stable (unstable) static wormhole solutions for various physical parametric values and illustrate them graphically.

Spherically symmetric wormholes in minimally coupled f(R,T) gravity

In this manuscript, we construct a spherical thin shell wormhole in the background of the minimally coupled f(R, T) model. In this gravitational theory, f is an arbitrary functional form that depends on the Ricci scalar (R) as well as the trace of stress-energy tensor (T). To continue our systematic analysis, we use a cut and paste approach to link two surfaces, i.e., interior and exterior. We find energy-momentum density along with surface pressure for f(R, T) gravitational f(R, T) = R + α R 2 + λ T model, by using the Lanczos equation. We utilize the polytropic equation of state to check the dynamical behavior of the wormhole. A standard potential approach is applied to check the stability of constructed wormhole with throat radius a 0. Graphical analysis shows that the stability regions of wormholes rely on the specific values mass M to charge Q ratio.

Existence of energy density homogeneity for radiating spheres in f ( G , T ) gravity

This work discusses the responsible quantities of the emergence inhomogeneity by taking locally anisotropic radiating fluid in [Formula: see text] theory, where T and [Formula: see text] indicate the trace of stress energy tensor and Gauss–Bonnet terms. The temporal and radial change in mass function is observed with the help of a modified version of Einstein’s field equations. To observe the dynamics of self-gravitating fluid, the dynamical equations and differential equations for conformal tensor are constructed, which help to understand the role of correction terms, Weyl curvature, and fluid parameter in the energy–density irregularity. Various forms of fluid are addressed to meet the desired results.

The bouncing cosmic behavior with logarithmic law [formula omitted] model

In this paper, we study the bouncing behavior of our universe under f(G,T) theory, by taking Friedmann–Lemaître–Robertson–Walker metric, which is assumed to be coupled with an ideal fluid distribution. Here G is the Gauss–Bonnet scalar and T is the trace of stress energy tensor. The corresponding field equations are explored after assuming two specific forms of Hubble parameter in the presence of f(G,T)=G(log(ςG))+2λT correction terms. The energy bounds are examined analytically to provide necessary explanations for the theoretical phenomenon of cosmic bounce. The equation of state parameter, deceleration parameter, jerk and snap are also evaluated, accompanied by the associated dynamical parameters. With constraints-based model parameters, the modified geometrical action is configured to work for the removal of initial singularity.

The Coupling effects of f(R,Tϕ) gravity on axial gravitational waves

The motive of this paper is to study the axial type gravitational waves within flat FRW universe and in the context of f ( R , T ϕ ) gravity (where T ϕ corresponds to the trace of stress energy tensor of ϕ , a scalar field). For this purpose, we consider the famous Regge–Wheeler axial perturbation scheme for geometry as well as assume the corresponding perturbations in the scalar field. We derived the field equations for both unperturbed and axially perturbed scenarios. The simultaneous solution of both sets of field equations lead to some expressions for unknown perturbation parameters. In view of these expressions, we concluded that the propagation of axial gravitational waves is influenced by the scalar field potential and the coupling of geometry and scalar field. The plots of conformal time function emanating from axial metric perturbations, for different values of λ and β , indicate this impact. • Our work is in Modified gravity. • Many researchers which are working in GR not appreciated the Modified gravity.

Quasi static evolution of compact objects in modified gravity

In this paper, the quasi static-approximation on the hydrodynamics of compact objects is proposed in f(R, T) gravity, where R is the scalar curvature and T is the trace of stress-energy tensor, by exploring the axial and reflection symmetric spacetime stuffed with anisotropic and dissipative matter contents. The set of invariant-velocities is defined to comprehend the concept of quasi static-approximation. As a consequence, the evolution of compact objects is shown by analyzing the corresponding modified field, dynamical and scalar equations in this approximation to evoke all the feasible outcomes. Furthermore, the significance of kinematical quantities, modified heat-fluxes and scalar variables are found through the proposed approximation.

Wormhole modeling in f(R,T) gravity with minimally-coupled massless scalar field

In this paper, the strong gravitational lensing is explored for traversable wormholes in [Formula: see text] theory of gravity with minimally-coupled massless scalar field. First, the effective wormhole solutions are obtained using the model [Formula: see text], where [Formula: see text] is constant, [Formula: see text] is scalar curvature and [Formula: see text] is the trace of stress-energy tensor. Furthermore, three different shape functions namely, [Formula: see text] (Ref. 36), [Formula: see text] (Refs. 35 and 37) and [Formula: see text], [Formula: see text] (Refs. 34, 35, 39, 73) are considered and studied their qualitative behavior for the construction of wormhole geometry respectively. Subsequently, gravitational lensing effect is implemented to detect the existence of photon spheres at or outside the throat of wormholes.

Evolution of the charged dynamical radiating spherical structures

In the scenario of f(R,T,Q) gravity, where R and T represent the Ricci scalar and the trace of stress energy tensor respectively, and Q≡RμνTμν, we generalize the concept of complexity for dissipative dynamical spherically self-gravitating fluid configuration proposed by Herrera et al. (2018). As the fluid contains dynamical situation, we evaluate the structural complexity as well as the complexity of the pattern of evolution for matter configuration in the presence of electric charge and check their viability under f(R,T,Q) correction terms. In the context of modified gravity, we calculate some dynamical and kinematical equations in both dissipative and nondissipative phenomena. Eventually, we construct the equations for the structural scalars evolution and consistency of the condition at which the complexity factor disappears. For f(R,T,Q)=R in modified action, all of our results reduce to general relativity.

Cosmological dynamics in R2 gravity with logarithmic trace term

A novel function for modified gravity is proposed, f(R,T)=R+λR2+2βln(T), with constants λ and β, scalar curvature R, and the trace of stress energy tensor T, satisfying T=ρ−3p>0. Subsequently, two equations of state (EoS) parameters, namely ω and a parametric form of the Hubble parameter H, are employed in order to study the accelerated expansion and initial cosmological bounce of the corresponding universe. Hubble telescope experimental data for redshift z within the range 0.07≤z≤2.34 are used to compare the theoretical and observational values of the Hubble parameter. Moreover, it is observed that all the energy conditions are fulfilled within a neighborhood of the bouncing point t=0, what shows that the necessary condition for violation of the null energy condition, within a neighborhood of the bouncing point in general relativity, could be avoided by modifying the theory in a reasonable way. Furthermore, a large amount of negative pressure is found, which helps to understand the late time accelerated expansion phase of the universe.

Estimation of cosmological parameters, stability analysis and energy conditions in viable modified gravity

In the present paper, we have investigated the Friedmann-Robertson-Walker (FRW) model in viable f(R, T) gravity with f(R, T) function proposed as f(R,T)=R+ξT1/2, where ξ is an arbitrary constant, R is the scalar curvature and T is the trace of stress energy tensor. Defining the scale factor, the field equations are solved numerically and the energy conditions are analyzed. Further, determining Hubble parameter and deceleration parameter, their present values are estimated. Furthermore, 57 redshift data (42 redshift data from Supernova Cosmology project and 15 redshift data from Calán/ Tolono Supernova survey) are used to estimate the age of the universe and to find the best fit curves for luminosity distance and apparent magnitude.

Locally rotationally symmetric Bianchi type-II cosmological model in f(R, T) gravity

The present work is focused on the study of locally rotationally symmetric Bianchi type-II model with perfect fluid in f(R, T) gravity. Three types of f(R, T) gravity models are proposed (Harko et al. in Phys Rev D 84:024020, 2011). According to the first model, the function $$f(R,T)=R+2f(T)$$ , where R is Ricci scalar and f(T) is an arbitrary function of trace of stress energy tensor T. In this paper, the function $$f(T) = \alpha T + \beta T^2$$ is considered, where $$\alpha$$ and $$\beta$$ are real numbers. The physical parameters are determined with respect to cosmic time as well as red shift by using the equation of state $$p=\epsilon \rho$$ and the scale factor $$a(t) = (\sinh (\phi t))^{\frac{1}{k}}$$ , where $$k>0$$ & $$\phi \ne 0$$ . The energy density is compared for dust and radiation-dominated models. The present values of deceleration parameter, Hubble parameter and age of the universe are determined and compared with the results of $$\Lambda$$ CDM model. Further, the theoretical and experimental values of luminosity distance and apparent magnitude are compared.

Existence of wormhole solutions and energy conditions in f(R, T) gravity

This paper is devoted to investigate the spherically symmetric wormhole models in f(R, T) gravity, where T and R are trace of stress energy tensor and the Ricci scalar, respectively. In this context, we discuss three distinct cases of fluid distributions viz, anisotropic, barotropic and isotropic matter contents. After considering the exponential f(R, T) model, the behavior of energy conditions are analyzed that will help us to explore the general conditions for wormhole geometries in this gravity. It is inferred that the usual matter in the throat could obey the energy conditions but the gravitational field emerging from higher order terms of modified gravity favor the existence of the non-standard geometries of wormholes. The stability as well as the existence of wormholes are also analyzed in this theory.

Higher-dimensional gravitational collapse of perfect fluid spherically symmetric spacetime in f(R, T) gravity

In this paper, our aim is to study (n + 2)-dimensional collapse of perfect fluid spherically symmetric spacetime in the context of f(R, T) gravity. The matching conditions are acquired by considering a spherically symmetric non-static (n + 2)-dimensional metric in the inner region and Schwarzschild (n + 2)-dimensional metric in the outer region of the star. To solve the field equations for above settings in f(R, T) gravity, we choose the stress–energy tensor trace and the Ricci scalar as constants. It is observed that two physical horizons, namely, cosmological and black hole horizons appear as a consequence of this collapse. A singularity is also formed after the birth of both the horizons. It is also observed that the term f(R0, T0) slows down the collapsing process.

Modified Gauss\u2013Bonnet gravity with radiating fluids

The main purpose of this paper is to discuss structure scalars in the context of f(mathcal {G}, T) gravity, where mathcal {G} is the Gauss–Bonnet invariant and T is the trace of stress energy tensor. For this aim, we have considered the spherically symmetric spacetime and dissipative anisotropic fluid coupled with radiation and heat ejecting shearing matter distributions. We have found these scalar variables by orthogonally decomposing the Riemann curvature tensor in f(mathcal {G}, T) gravity. Moreover, the evolution equations of shear and expansion are also developed with the help of these scalar functions. We have also analysed these scalars by taking mathcal {G} and T as constants for dust cloud. The physical behaviour of structure scalars for radiating matter distributions has been examined in the presence of modified gravity. It is shown that the evolutionary stages of relativistic stellar structures can be explored via modified scalar functions.

Dynamical analysis of cylindrically symmetric anisotropic sources in f(R,\xa0T) gravity

In this paper, we have analyzed the stability of cylindrically symmetric collapsing object filled with locally anisotropic fluid in f(R, T) theory, where R is the scalar curvature and T is the trace of stress-energy tensor of matter. Modified field equations and dynamical equations are constructed in f(R, T) gravity. The evolution or collapse equation is derived from dynamical equations by performing a linear perturbation on them. The instability range is explored in both the Newtonian and the post-Newtonian regimes with the help of an adiabetic index, which defines the impact of the physical parameters on the instability range. Some conditions are imposed on the physical quantities to secure the stability of the gravitating sources.

Scalar field with the source in the form of the stress-energy tensor trace as a dark energy model

We consider a scalar-tensor theory of gravitation with the scalar source being the trace of the stress-energy tensor of the scalar field itself and matter. We obtain an example of a numerical solution of the cosmological equations which shows that under some special choice of the scalar parameters, there exists a slow-roll regime in which the modern values of the Hubble and deceleration parameters may be obtained.

A dynamical system analysis of f(R,T) gravity

We investigate equations of motion and future singularities of [Formula: see text] gravity where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of stress-energy tensor. Future singularities for two kinds of equation of state (barotropic perfect fluid and generalized form of equation of state) are studied. While no future singularity is found for the first case, some kind of singularity is found to be possible for the second. We also investigate [Formula: see text] gravity by the method of dynamical systems and obtain some fixed points. Finally, the effect of the Noether symmetry on [Formula: see text] is studied and the consistent form of [Formula: see text] function is found using the symmetry and the conserved charge.

Static spherically symmetric wormholes in f(R, T) gravity

In this work, we explore wormhole solutions in $f(R,T)$ theory of gravity, where $R$ is the scalar curvature and $T$ is the trace of stress-energy tensor of matter. To investigate this, we consider static spherically symmetric geometry with matter contents as anisotropic, isotropic and barotropic fluids in three separate cases. By taking into account Starobinsky $f(R)$ model , we analyze the behavior of energy conditions for these different kind of fluids. It is shown that the wormhole solutions can be constructed without exotic matter in few regions of spacetime. We also give the graphical illustration of obtained results and discuss the equilibrium picture for anisotropic case only. It is concluded that the wormhole solutions with anisotropic matter are realistic and stable in this gravity.

Black hole spectra in holography: Consequences for equilibration of dual gauge theories

For a closed system to equilibrate from a given initial condition there must exist an equilibrium state with the energy equal to the initial one. Equilibrium states of a strongly coupled gauge theory with a gravitational holographic dual are represented by black holes. We study the spectrum of black holes in Pilch–Warner geometry. These black holes are holographically dual to equilibrium states of strongly coupled SU(N) N=2⁎ gauge theory plasma on S3 in the planar limit. We find that there is no energy gap in the black hole spectrum. Thus, there is a priori no obstruction for equilibration of arbitrary low-energy states in the theory via a small black hole gravitational collapse. The latter is contrasted with phenomenological examples of holography with dual four-dimensional CFTs having non-equal central charges in the stress–energy tensor trace anomaly.

Dynamical analysis of self-gravitating stars in f(R,T) gravity

We study the factors affecting the stability of a locally isotropic spherical self-gravitating systems in f(R,T) gravity, where R is the Ricci curvature invariant and T is the trace of stress-energy tensor. Specifically, the collapse equation is obtained from conservation laws with non-null expansion scalar at Newtonian and post-Newtonian approximations. Initially, we consider the hydrostatic phase of the system which upon radial perturbation provides linearized field equations. This approach gives rise to specific instability constraints to ensure the collapsing behavior of the spherical isotropic fluid distribution. Finally, we discuss the role played by matter variables in this perspective.