scholarly journals Cosmological meaning of geometric curvatures

Filomat ◽  
2020 ◽  
Vol 34 (12) ◽  
pp. 4107-4121
Author(s):  
Nenad Vesic
Keyword(s):  
Energy Density ◽  
Physical Meaning ◽  
Riemannian Space ◽  
Energy Momentum Tensor ◽  
State Parameter ◽  
Momentum Tensor ◽  
The State ◽  
Generalized Riemannian Space ◽  
Riemannian Spaces

In this paper, we analyzed the physical meaning of scalar curvatures for a generalized Riemannian space. It is developed the Madsen?s formulae for pressures and energy-densities with respect to the corresponding energy-momentum tensors. After that, the energy-momentum tensors, pressures, energy-densities and state-parameters are analyzed with respect to different concepts of generalized Riemannian spaces. At the end of this paper, linearities of the energy-momentum tensor, pressure, energy-density and the state-parameter are examined.

scholarly journals Spinor Quintom Cosmology with Intrinsic Spin

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Emre Dil
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Dark Energy Model ◽  
Energy Momentum Tensor ◽  
State Parameter ◽  
Momentum Tensor ◽  
Big Rip ◽  
Equation Of State Parameter ◽  
Spin Contribution ◽  
Distance Parameter

We consider a spinor quintom dark energy model with intrinsic spin, in the framework of Einstein-Cartan-Sciama-Kibble theory. After constructing the mathematical formalism of the model, we obtain the spin contributed total energy-momentum tensor giving the energy density and the pressure of the quintom model, and then we find the equation of state parameter, Hubble parameter, deceleration parameter, state finder parameter, and some distance parameter in terms of the spinor potential. Choosing suitable potentials leads to the quintom scenario crossing between quintessence and phantom epochs, or vice versa. Analyzing three quintom scenarios provides stable expansion phases avoiding Big Rip singularities and yielding matter dominated era through the stabilization of the spinor pressure via spin contribution. The stabilization in spinor pressure leads to neglecting it as compared to the increasing energy density and constituting a matter dominated stable expansion epoch.

scholarly journals Anisotropic Universe in f(G,T) Gravity

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
M. Farasat Shamir
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Energy Momentum Tensor ◽  
State Parameter ◽  
Momentum Tensor ◽  
Anisotropic Universe ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Physical Quantities ◽  
Bonnet Term

This paper is devoted to investigating the recently introduced f(G,T) theory of gravity, where G is the Gauss-Bonnet term and T is the trace of the energy-momentum tensor. For this purpose, anisotropic background is chosen and a power law f(G,T) gravity model is used to find the exact solutions of field equations. In particular, a general solution is obtained which is further used to reconstruct some important solutions in cosmological contexts. The physical quantities like energy density, pressure, and equation of state parameter are calculated. A Starobinsky-like f2(T) model is proposed which is used to analyze the behavior of universe for different values of equation of state parameter. It is concluded that presence of term T in the bivariate function f(G,T) may give many cosmologically important solutions of the field equations.

scholarly journals Positive Energy Driven CTCs In ADM 3+1 Space – Time of Unprotected Chronology

2021 ◽  
Author(s):  
Deep Bhattacharjee
Keyword(s):  
Energy Density ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Space Time ◽  
Exotic Matter ◽  
Positive Energy ◽  
Spacelike Hypersurfaces ◽  
Stress Energy ◽  
Maxwell Fields ◽  
Stress Energy Momentum Tensor

Chronology unprotected mechanisms are considered with a very low gravitational polarization to make the wormhole traversal with positive energy density everywhere. No need of exotic matter has been considered with the assumption of the Einstein-Dirac-Maxwell Fields, encountering above the non-zero stress-energy-momentum tensor through spacelike hypersurfaces by a hyperbolic coordinate shift.

scholarly journals A geometrical model for the evolution of spherical planetary nebulae based on thin-shell formalism

2021 ◽  
pp. 2150191
Author(s):  
Ibrahim Gullu ◽  
S. Habib Mazharimousavi ◽  
S. Danial Forghani
Keyword(s):  
Energy Density ◽  
Planetary Nebula ◽  
Thin Shell ◽  
Energy Momentum Tensor ◽  
Geometric Model ◽  
Geometrical Model ◽  
Momentum Tensor ◽  
Evolution Pattern ◽  
Simple Power Function ◽  
Curvature Tensors

A spherical planetary nebula is described as a geometric model. The nebula itself is considered as a thin-shell, which is visualized as a boundary of two spacetimes. The inner and outer curvature tensors of the thin-shell are found in order to get an expression of the energy-momentum tensor on the thin-shell. The energy density and pressure expressions are derived using the energy-momentum tensor. The time evolution of the radius of the thin-shell is obtained in terms of the energy density. The model is tested by using a simple power function for decreasing energy density and the evolution pattern of the planetary nebula is attained.

scholarly journals TRAPPING PHOTONS BY A LINE SINGULARITY

2003 ◽  
Vol 12 (06) ◽  
pp. 1095-1112 ◽  
Author(s):  
METIN ARIK ◽  
OZGUR DELICE
Keyword(s):  
Energy Density ◽  
Thin Shell ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Cylindrically Symmetric ◽  
Static Solutions ◽  
Line Singularity ◽  
Thick Shells

We present cylindrically symmetric, static solutions of the Einstein field equations around a line singularity such that the energy momentum tensor corresponds to infinitely thin photonic shells. Positivity of the energy density of the thin shell and the line singularity is discussed. It is also shown that thick shells containing mostly radiation are possible in a numerical solution.

scholarly journals EXOTIC LOW DENSITY FERMION STATES IN THE TWO MEASURES FIELD THEORY: NEUTRINO DARK ENERGY

2006 ◽  
Vol 21 (21) ◽  
pp. 4373-4406 ◽  
Author(s):  
E. I. GUENDELMAN ◽  
A. B. KAGANOVICH
Keyword(s):  
Field Theory ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Energy Momentum Tensor ◽  
Neutrino Energy ◽  
Momentum Tensor ◽  
Dark Energy Density ◽  
Two Measures ◽  
The Universe

There exist field theory models where the fermionic energy–momentum tensor contains a term proportional to [Formula: see text] which may contribute to the dark energy. We show that this new field theory effect can be achieved in the Two Measures Field Theory (TMT) in the cosmological context. TMT is an alternative gravity and matter field theory where the gravitational interaction of fermionic matter is reduced to that of General Relativity when the energy density of the fermion matter is much larger than the dark energy density. In this case also the fifth force problem is solved automatically. In the opposite limit, where the magnitudes of fermionic energy density and scalar field dark energy density become comparable, nonrelativistic fermions can participate in the cosmological expansion in a very unusual manner. Some of the features of such Cosmo-Low-Energy-Physics (CLEP) states are studied in a toy model of the late time universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos, and the following results are obtained: neutrino mass increases as m ∝ a3/2 (a is the scale factor); the proportionality factor in the noncanonical contribution to the neutrino energy–momentum tensor (proportional to the metric tensor) approaches a constant as a(t) → ∞ and therefore the noncanonical contribution to the neutrino energy density dominates over the canonical one ~ m/a3 ~ a-3/2 at the late enough universe; hence the neutrino gas equation-of-state approaches w = -1, i.e. neutrinos in the CLEP regime behave as a sort of dark energy as a → ∞; the equation-of-state for the total (scalar field + neutrino) energy density and pressure also approaches w = -1 in the CLEP regime; besides the total energy density of such universe is less than it would be in the universe filled with the scalar field alone. An analytic solution is presented. A domain structure of the dark energy seems to be possible. We speculate that decays of the CLEP state neutrinos may be both an origin of cosmic rays and responsible for a late super-acceleration of the universe. In this sense the CLEP states exhibit simultaneously new physics at very low densities and for very high particle masses.

scholarly journals Stress Tensor of Free Maxwell Field in Friedmann-Robertson-Walker Universe

1970 ◽  
Vol 7 (7) ◽  
pp. 1-2 ◽  
Author(s):  
SK Sharma ◽  
PR Dhungel ◽  
U Khanal
Keyword(s):  
Energy Density ◽  
Key Words ◽  
Stress Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Anisotropic Pressure ◽  
Translational Energy ◽  
Closed Universe ◽  
Scientific World ◽  
Friedmann Robertson Walker

The solutions of the Maxwellian field in FRW spacetime, found by using the Newman Penrose formalism, is used to determine the energy-momentum tensor. The tensor is obviously traceless, with the energy density equal to the sum of the radial and the two tangential pressures. But it turns out that the radial and tangential pressures are not equal, giving rise to anisotropy. Such anisotropy can be the origin of the rotation of galaxies. Another result is that the photon energy in a closed universe are quantized in units of one from the lowest value of two upwards. The lowest quantum of two can be interpreted as one unit of spin energy and one of translational energy. Key words: Galactic structure; Maxwellian field; Anisotropic pressure. DOI: 10.3126/sw.v7i7.3814 Scientific World Vol.7(7) 2009 pp.1-2

Further comments on the equivalence of Abraham's, Minkowski's, and others' electrodynamics

1980 ◽  
Vol 58 (8) ◽  
pp. 1163-1170 ◽  
Author(s):  
Gérard A. Maugin
Keyword(s):  
Energy Density ◽  
Total Energy ◽  
Mechanical Behavior ◽  
Internal Energy ◽  
Closed System ◽  
Ad Hoc ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Electromagnetic Energy ◽  
Time Decomposition

Arguments recently proposed by Kranyš concerning the nondistinguishability between Abraham's and Minkowski's electromagnetic contributions to the total energy-momentum tensor of the same relativistic, thermodynamically closed system are extended to other electromagnetic energy-momentum tensors (as proposed by Grot and Eringen and de Groot and Suttorp). The adjustment of the corresponding "matter" contribution, which occurs in each element of the canonical space-time decomposition of the total energy-momentum tensor, is exhibited in those different cases. For dissipation-free systems this adjustment can be achieved for each case by means of an ad hoc Legendre transformation on the internal energy density. The arguments used do not presuppose any isotropy and linearity of the medium and can be readily extended to the cases of media with hysteresis and media endowed with intrinsic spins, be they of a fluid-like or solid-like type of mechanical behavior.

scholarly journals DARK ENERGY FROM FIFTH-DIMENSIONAL BRANS–DICKE THEORY

2013 ◽  
Vol 22 (10) ◽  
pp. 1350070 ◽  
Author(s):  
AMIR F. BAHREHBAKHSH ◽  
MEHRDAD FARHOUDI ◽  
HAJAR VAKILI
Keyword(s):  
Dark Energy ◽  
Energy Momentum Tensor ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Scale Factor ◽  
The State ◽  
The Other ◽  
Distance Modulus ◽  
Fifth Dimension

Following the approach of the induced-matter theory, we investigate the cosmological implications of a five-dimensional Brans–Dicke (BD) theory, and propose to explain the acceleration of the universe. After inducing in a four-dimensional hypersurface, we classify the energy–momentum tensor into two parts in a way that, one part represents all kind of the matter (the baryonic and dark) and the other one contains every extra terms emerging from the scale factor of the fifth dimension and the scalar field, which we consider as the energy–momentum tensor of dark energy. We also separate the energy–momentum conservation equation into two conservation equations, one for matter and the other for dark energy. We perform this procedure for different cases, without interacting term and with two particular (suitable) interacting terms between the two parts. By assuming the parameter of the state equation for dark energy to be constant, the equations of the model admit the power-law solutions. Though, the noninteracting case does not give any accelerated universe, but the interacting cases give both decelerated and accelerated universes. For the interacting cases, we figure out analytically the acceptable ranges of some parameters of the model, and also investigate the data analysis to test the model parameter values consistency with the observational data of the distance modulus of 580 SNe Ia compiled in Union2.1. For one of these interacting cases, the best fitted values suggest that BD coupling constant (ω) is ≃ -7.75, however, it also gives the state parameter of dark energy (wX) equal to ≃ -0.67. In addition, the model gives the Hubble and deceleration parameters at the present time to be H◦ ≃ 69.4 (km/s)/Mpc and q◦ ≃ -0.38 (within their confidence intervals), where the scale factor of the fifth dimension shrinks with the time.

scholarly journals Spacetimes Admitting Concircular Curvaure Tensor in f(R) Gravity

2022 ◽  
Vol 9 ◽  
Author(s):  
Uday Chand De ◽  
Sameh Shenawy ◽  
H. M. Abu-Donia ◽  
Nasser Bin Turki ◽  
Suliman Alsaeed ◽  
...  
Keyword(s):  
Energy Density ◽  
Perfect Fluid ◽  
Curvature Tensor ◽  
Ricci Tensor ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Isotropic Pressure ◽  
Concircular Curvature Tensor ◽  
Fluid Spacetimes

The main object of this paper is to investigate spacetimes admitting concircular curvature tensor in f(R) gravity theory. At first, concircularly flat and concircularly flat perfect fluid spacetimes in fR gravity are studied. In this case, the forms of the isotropic pressure p and the energy density σ are obtained. Next, some energy conditions are considered. Finally, perfect fluid spacetimes with divergence free concircular curvature tensor in f(R) gravity are studied; amongst many results, it is proved that if the energy-momentum tensor of such spacetimes is recurrent or bi-recurrent, then the Ricci tensor is semi-symmetric and hence these spacetimes either represent inflation or their isotropic pressure and energy density are constants.

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