Perfect Fluid Energy-momentum Tensor Research Articles

Energy condition of wormhole and thin shell by assuming conformal symmetry in teleparallel-Rastall gravity

The static spherically symmetric wormhole solution for a non-isotropic perfect fluid energy-momentum tensor within the context of teleparallel-Rastall gravity is investigated. First, by imposing static and non-static conformal symmetry on the static spherically symmetric space-time metric, we investigated the null energy condition at the throat of traversable wormholes and showed that the null energy condition in the throat and its neighborhood is violated. Secondly, with the aim of minimize the usage of exotic matter, we found regions where the energy conditions are valid at the junction surface. We found that in the static case of conformal symmetry solution, the null energy condition (NEC), weak energy condition (WEC), and Strong energy condition (SEC) are valid for different λ 0 parameters. Moreover, we obtained that for the non-static symmetric solution of conformal symmetry, the NEC and WEC are satisfied for different sets of parameters. Finally, we have explored the stable regions by the parameter η 2 (square speed of sound) for different sets of parameters.

Buchdahl quark stars within f(Q) theory

In the present paper, authors study the strange stars with the MIT Bag EoS admitting Buchdahl symmetry (non-singular and physically viable metric potential) in the both linear $$f(Q)=aQ+b$$ and nonlinear $$f(Q)=Q+aQ^b$$ forms of modified symmetric teleparallel gravitation. In order to obtain the correct form of Buchdahl metric coefficients, they matched interior strange star space-time with the exterior Schwarzschild vacuum space-time. As a strange star candidate, PSRJ1416-2230 has been used with mass $$M=1.69M_\odot$$ and radius $$R=9.69R_\odot$$ . For either linear and nonlinear f(Q) gravities, they probed Null, Dominant and Strong Energy Conditions as well as the radial, tangential Equation of State (EoS), gradients of the perfect fluid energy-momentum tensor elements, Tolman–Oppenheimer–Volkoff equilibrium condition, relativistic adiabatic index and causality conditions, surface redshift. It was found that strange stars in the linear and nonlinear f(Q) gravity show physically viable behavior, respect energy and causality conditions, has EoS in the bounds $$0\le \omega \le 1$$ and surface redshift does not exceed 2, as expected.

Higher-Dimensional Regular Reissner–Nordström Black Holes Associated with Linear Electrodynamics

Following the interpretation of matter source that the energy-momentum tensor of anisotropic fluid can be dealt with effectively as the energy-momentum tensor of perfect fluid plus linear (Maxwell) electromagnetic field, we obtain the regular higher-dimensional Reissner–Nordström (Tangherlini–RN) solution by starting with the noncommutative geometry-inspired Schwarzschild solution. Using the boundary conditions that connect the noncommutative Schwarzschild solution in the interior of the charged perfect fluid sphere to the Tangherlini–RN solution in the exterior of the sphere, we find that the interior structure can be reflected by an exterior parameter, the charge-to-mass ratio. Moreover, we investigate the stability of the boundary under mass perturbation and indicate that the new interpretation imposes a rigid restriction upon the charge-to-mass ratio. This restriction, in turn, permits a stable noncommutative black hole only in the 4-dimensional spacetime.

Neutron stars in Scalar-Tensor-Vector Gravity

Scalar-Tensor-Vector Gravity (STVG), also referred as MOdified Gravity (MOG), is an alternative theory of the gravitational interaction. Its weak field approximation has been successfully used to described Solar System observations, galaxy rotation curves, dynamics of clusters of galaxies, and cosmological data, without the imposition of dark components. The theory was formulated by John Moffat in 2006. In this work, we derive matter-sourced solutions of STVG and construct neutron star models. We aim at exploring STVG predictions about stellar structure in the strong gravity regime. Specifically, we represent spacetime with a static, spherically symmetric manifold, and model the stellar matter content with a perfect fluid energy-momentum tensor. We then derive the modified Tolman-Oppenheimer-Volkoff equation in STVG and integrate it for different equations of state. We find that STVG allows heavier neutron stars than General Relativity (GR). Maximum masses depend on a normalized parameter that quantifies the deviation from GR. The theory exhibits unusual predictions for extreme values of this parameter. We conclude that STVG admits suitable spherically symmetric solutions with matter sources, relevant for stellar structure. Since recent determinations of neutron stars masses violate some GR predictions, STVG appears as a viable candidate for a new gravity theory.

Cosmological model dependence of the galaxy luminosity function: far-infrared results in the Lemaître-Tolman-Bondi model

This is the first paper of a series aiming at investigating galaxy formation and evolution in the giant-void class of the Lemaitre-Tolman-Bondi (LTB) models that best fits current cosmological observations. Here we investigate the Luminosity Function (LF) methodology, and how its estimates would be affected by a change on the cosmological model assumed in its computation. Are the current observational constraints on the allowed Cosmology enough to yield robust LF results? We use the far-infrared source catalogues built on the observations performed with the Herschel/PACS instrument, and selected as part of the PACS evolutionary probe (PEP) survey. Schechter profiles are obtained in redshift bins up to z approximately 4, assuming comoving volumes in both the standard model, that is, Friedmann-Lemaitre-Robertson-Walker metric with a perfect fluid energy-momentum tensor, and non-homogeneous LTB dust models, parametrized to fit the current combination of results stemming from the observations of supernovae Ia, the cosmic microwave background, and baryonic acoustic oscillations. We find that the luminosity functions computed assuming both the standard model and LTB void models show in general good agreement. However, the faint-end slope in the void models shows a significant departure from the standard model up to redshift 0.4. We demonstrate that this result is not artificially caused by the used LF estimator which turns out to be robust under the differences in matter-energy density profiles of the models. The differences found in the LF slopes at the faint end are due to variation in the luminosities of the sources, which depend on the geometrical part of the model. It follows that either the standard model is over-estimating the number density of faint sources or the void models are under-estimating it.

Analytical Solution of a Wave Equation in Cosmology

In this paper we derive a wave equation based on a cosmological model of the universe expansion in the four-dimensional space-velocity. An analytical solution of this equation is obtained using Nikiforov-Uvarov mathematical method. In this procedure we use the solutions of the Einstein gravitational field equations for the perfect fluid energy-momentum tensor.

General relativistic spinning fluids with a modified projection tensor

An energy-momentum tensor for general relativistic spinning fluids compatible with Tulczyjew-type supplementary condition is derived from the variation of a general Lagrangian with unspecified explicit form. This tensor is the sum of a term containing the Belinfante-Rosenfeld tensor and a modified perfect-fluid energy-momentum tensor in which the four-velocity is replaced by a unit four-vector in the direction of fluid momentum. The equations of motion are obtained and it is shown that they admit a Friedmann-Robertson-Walker space-time as a solution.

Noncommutative closed Friedman universe

Heller et al. (J Math Phys 46:122501, 2005; Int J Theor Phys 46:2494, 2007) proposed a model unifying general relativity and quantum mechanics based on a noncommutative algebra \({\mathcal{A}}\) defined on a groupoid having the frame bundle over space–time as its base space. The generalized Einstein equation is assumed in the form of the eigenvalue equation of the Einstein operator on a module of derivations of the algebra \({\mathcal{A}}\) . No matter sources are assumed. The closed Friedman world model, when computed in this formalism, exhibits two interesting properties. First, generalized eigenvalues of the Einstein operator reproduce components of the perfect fluid energy-momentum tensor for the usual Friedman model together with the corresponding equation of state. One could say that, in this case, matter is produced out of pure (noncommutative) geometry. Second, owing to probabilistic properties of the model, in the noncommutative regime (on the Planck level) singularities are irrelevant. They emerge in the process of transition to the usual space–time geometry. These results are briefly discussed.

Higher Dimensional FRW Cosmological Models in Self-Creation Theory

The field equations of Barber's (1982) second self-creation theory of gravitation are solved for 5D Friedmann-Robertson-Walker space time using perfect fluid energy momentum tensor. By assuming an equation of state p= e ρ, (0 ≤ e ≤ 1), the solutions of the field equations, in different scenarios, in Barber's second self-creation theory are presented and discussed. Some properties of these models are also discussed.

Space-time geometry and thermodynamic properties of a self-gravitating ball of fluid in phase transition

A numerical solution of Einstein field equations for a spherical symmetric and stationary system of identical and auto-gravitating particles in phase transition is presented. The fluid possess a perfect fluid energy momentum tensor, and the internal interactions of the system are represented by a van der Walls like equation of state able to describe a first order phase transition of the type gas-liquid. We find that the space-time curvature, the radial component of the metric, and the pressure and density show discontinuities in their radial derivatives in the phase coexistence region. This region is found to be a spherical surface concentric with the star and the system can be thought as a foliation of acronal, concentric and isobaric surfaces in which the coexistence of phases occurs in only one of these surfaces. This kind of system can be used to represent a star with a high energy density core and low energy density mantle in hydrodynamic equilibrium.

Dimensionally continued wormhole solutions.

In this paper we consider wormhole solutions for the action of ``special Lovelock gravity'' recently discussed by Banados, Teitelboim, and Zanelli. This action is, in odd dimensions, the Chern-Simons form for the anti--de Sitter group and, in even dimensions, the Euler density constructed with the Lorentz part of the anti--de Sitter curvature tensor. We present a systematic study of classical wormhole solutions in the special Lovelock theory with various matter content, including a perfect fluid energy-momentum tensor, axionic field, and conformal scalar field.

Wormhole Solutions with Perfect Fluid Energy-Momentum Tensors

Wormhole solutions are found in various theories with a perfect fluid energy-momentum tensor added to the right-hand side of classical Euclidean-Einstein equation. We found that wormhole solutions indeed exist for a lot of models in the presence of such a perfect fluid energy-momentum tensor, which is coincident with the conclusion obtained by Hawking and Page.

Perfect maxwell fluids in the standard cosmology

We provide closed form solutions to the Maxwell equations for the modes associated with the propagation of classical electromagnetic radiation in background Robertson-Walker geometries of any allowed spatial curvature. An incoherent averaging over complete sets of these modes in each spatial geometry is then found to yield the familiar perfect fluid energy-momentum tensor required of the standard Friedmann cosmology.

Consistency relations for spinning matter in gravitational theories.

We explore the consistency equations that result from Euler's equations for the improved perfect-fluid energy-momentum tensor for a charged spinning fluid in the Einstein-Cartan theory.Received 25 August 1986DOI:https://doi.org/10.1103/PhysRevD.34.3268©1986 American Physical Society

The perfect-fluid tensor in the non-symmetric theory of gravitation

The perfect-fluid energy-momentum tensor in the non-symmetric gravitation theory (NGT) is derived using a fluid variational technique. Two different approaches are used. The first involves conservation of rest mass as a fundamental fluid constraint in the total Lagrangian while the second involves the assumption of an equation of state P=P( rho 0). The relativistic fluid conservation equation and the Euler equation of motion for NGT are obtained using the derived fluid tensor.

Improved Perfect-Fluid Energy-Momentum Tensor with Spin in Einstein-Cartan Space-Time

An improved perfect-fluid energy-momentum tensor including spin and torsion is presented with use of a Lagrangian variational principle based upon the tetrad formalism of Halbwach and the method of constraints of Ray.