Murat Korunur

Creation of spin-1/2 particles in de Sitter space–time

Abstract In this work we analyzed the particle creation process of spin-1/2 particles by considering a simple cosmological model, a two-dimensional de Sitter space–time. We choose two different charts, the static and global chart, on de Sitter space–time. We solved the Dirac equation for these two charts and then used Bogoliubov coefficients to relate vacuum states in the asymptotic regions of gravitational backgrounds. By using the Bogoliubov transformation technique we compute the density of particles created.

Finding Dirac Spin Effect in NUT Spacetime

In the present study, we are interested in finding the spin precession of a Dirac particle in expanding and rotating NUT spacetime. A tetrad with two functions to be determined is applied to the field equation of the teleparallel theory of gravity via a coordinate transformation. The vector, the axial-vector and the tensor parts of the torsion tensor are obtained. We found that the vector parts are in the radial and -directions. The axial-vector torsion is along r-direction while its other components along θ and -directions vanish everywhere. The vector connected with Dirac spin has been evaluated as well.

Energy Associated with the Gibbons-Maeda Dilaton Spacetime

In order to obtain energy and momentum (due to matter and fields including gravitation) distributions of the Gibbons-Maeda dilaton spacetime, we use the Møller energy-momentum prescription both in Einsteins theory of general relativity and teleparallel gravity. We find the same energy distribution for a given metric in both of these different gravitation theories. Under two limits, we also calculate energy associated with two other models such as the Garfinkle-Horowitz-Strominger dilaton spacetime and the Reissner-Nordstrom spacetime. The energy obtained is also independent of the teleparallel dimensionless coupling constant, which means that it is valid in any teleparallel model. Our result also sustains (a) the importance of the energy-momentum definitions in the evaluation of the energy distribution for a given spacetime and (b) the viewpoint of Lessner that the Møller energy-momentum complex is a powerful concept of energy and momentum (c) the hypothesis of Vagenas that there is a connection between the coefficients of the energy-momentum expression of Einstein and those of Møller.

f(T,R) theory of gravity

We mainly focus on the idea that the dynamics of the whole universe may be understood by making use of torsion T and curvature R at the same time. The f(T,R)-gravity can be considered as a fundamental gravitational theory describing the evolution of the universe. The model can produce the unification of the general relativity (GR), teleparallel gravity (TPG), f(R)-gravity and f(T)-gravity theories. For this purpose, the corresponding Lagrangian density is written in terms of an arbitrary function of the torsion and curvature scalars. Furthermore, we use the absence/existence puzzle of relativistic neutron stars and thermodynamical laws as constraining tools for the new proposal.

THE LUKASH PLANE-WAVE ATTRACTOR AND RELATIVE ENERGY

We study energy distribution in the context of teleparallel theory of gravity, due to matter and fields including gravitation, of the universe based on the plane-wave Bianchi VIIδ spacetimes described by the Lukash metric. For this calculation, we consider the teleparallel gravity analogs of the energy–momentum formulations of Einstein, Bergmann–Thomson and Landau–Lifshitz. We find that Einstein and Bergmann–Thomson prescriptions agree with each other and give the same results for the energy distribution in a given spacetime, but the Landau–Lifshitz complex does not. Energy density turns out to be nonvanishing in all of these prescriptions. It is interesting to mention that the results can be reduced to the already available results for the Milne universe when we write ω = 1 and Ξ2 = 1 in the metric of the Lukash spacetime, and for this special case, we get the same relation among the energy–momentum formulations of Einstein, Bergmann–Thomson and Landau–Lifshitz as obtained for the Lukash spacetime. Furth...

An axially symmetric scalar field and teleparallelism

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/0203084, gr-qc/0607138, gr-qc/0011087, gr-qc/0102070, gr-qc/0607138, gr-qc/0109017, gr-qc/0212018, and gr-qc/9409039.

Brane-world black holes and energy-momentum vector

The Brane-World black hole models are investigated to evaluate their relative energy and momentum components. We consider Einstein and Mollers energy-momentum prescriptions in general relativity, and also perform the calculation of energy-momentum density in Mollers tetrad theory of gravity. For the Brane-World black holes we show that although Einstein and Moller complexes, in general relativity give different energy relations, they yield the same results for the momentum components. In addition, we also make the calculation of the energy-momentum distribution in teleparallel gravity, and calculate exactly the same energy as that obtained by using Mollers energy-momentum prescription in general relativity. This interesting result supports the viewpoint of Lessner that the Moller energy-momentum complex is a powerful concept for the energy and momentum. We also give five different examples of Brane-World black holes and find the energy distributions associated with them. The result calculated in teleparallel gravity is also independent of the teleparallel dimensionless coupling constant, which means that it is valid in any teleparallel model. This study also sustains the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given space-time, and supports the hypothesis by Cooperstock that the energy is confined to the region of non-vanishing energy-momentum tensor of matter and all non-gravitational fields.

EXACT SOLUTIONS OF THE PHOTON EQUATION IN ANISOTROPIC SPACETIMES

In this paper we study the solution of the photon equation (the Massless Duffin–Kemmer–Petiau equation (mDKP)) in anisotropic expanding the Bianchi-I type spacetime using the Fourier analyze method. The harmonic oscillator behavior of the solutions is found. It is shown that Maxwell equations are equivalent to the photon equation.

Holographic reconstruction of scalar fields in extended Kaluza–Klein cosmology

In recent years, many studies have been conducted to reconstruct the physical properties of scalar fields by establishing a connection between some energy densities and a scalar field of dark energ...

Gödel-type spacetimes in f(R)-gravity

We focus on one of the famous problems in theoretical physics today: the problem of energy-momentum localization. Although many authors have endeavoured to solve this problem, it has remained unsolved until now. In this work, we consider the generalized version of the Landau-Lifshitz definition in f(R)-Gravity to discuss the energy-momentum localization problem in Gödel-type metrics. We also take into account five popular f(R) models to obtain specific results.