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Öğe An axially symmetric scalar field and teleparallelism(Springer, 2007) Korunur, M.; Salti, M.; Aydogdu, O.An axially symmetric scalar field is considered in teleparallel gravity. We calculate, respectively, the tensor, the vector and the axial-vector parts of torsion and energy, momentum and angular momentum in the ASSF. We find the vector parts are in the radial and (e) over cap (theta) directions, the axial-vector, momentum and angular momentum vanish identically, but the energy distribution is different from zero. The vanishing axial-vector part of torsion gives us the result that there occurs no deviation in the spherical symmetry of the spacetime. Consequently, there exists no inertia field with respect to a Dirac particle, and the spin vector of a Dirac particle becomes constant. The result for the energy is the same as obtained by Radinschi. Next, this work also (a) supports the viewpoint of Lessner that the Moller energy-momentumcomplex is a powerful concept for the energy-momentum, (b) sustains the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given spacetime, and (c) supports the hypothesis by Cooperstock that the energy is confined to the region of non-vanishing energy-momentumtens or of the matter and all non-gravitational fields.Öğe Extended Ricci and holographic dark energy models in fractal cosmology(Springer Heidelberg, 2014) Salti, M.; Korunur, M.; Acikgoz, I.We consider the fractal Friedmann-Robertson-Walker universe filled with dark fluid. By making use of this assumption, we discuss two types of dark energy models: Generalized Ricci and generalized holographic dark energies. We calculate the equation-of-state parameters, investigate some special limits of the results and discuss the physical implications via graphs. Also, we reconstruct the potential and the dynamics of the quintessence and k-essence (kinetic-quintessence) according to the results obtained for the fractal dark energy.Öğe Finding Dirac Spin Effect in NUT Spacetime(Iop Publishing Ltd, 2010) Korunur, M.; Salti, M.; Acikgoz, I.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 phi-directions. The axial-vector torsion is along r-direction while its other components along theta and phi-directions vanish everywhere. The vector connected with Dirac spin has been evaluated as well.Öğe Ghost DBI-essence in fractal geometry(Springer Heidelberg, 2016) Acikgoz, I.; Binbay, F.; Salti, M.; Aydogdu, O.Focusing on a fractal geometric ghost dark energy, we reconstruct the Dirac-Born-Infeld (DBI)-essence-type scalar field and find exact solutions of the potential and warped brane tension. We also discuss statefinders for the selected dark energy description to make it distinguishable among others.Öğe MATTER COLLINEATIONS OF BKS-TYPE SPACETIMES(Editura Acad Romane, 2014) Salti, M.; Korunur, M.; Acikgoz, I.; Binbay, F.; Pirinccioglu, N.In the present work, we classified the BKS-type (we refer to Bianchi-Kantowski-Sachs type spacetimes collectively as the BKS-type spacetimes) spacetimes (Bianchi type-V, Bianchi type-VI (m), Bianchi type-VI:(m), Kantowski-Sachs) according to their matter collineations when the energy-momentum tensor is degenerate and also when it is non-degenerate. We find that the dimension of matter collineations is infinite and we have improper matter collineations for the degenerate case (there are seven possibilities make the energy-momentum tensor to be degenerate). Next, for the non-degenerate case of the energy-momentum tensor, we obtain proper matter collineations and find the dimension of the group is finite.Öğe MIBc AND THE DIRAC SPIN EFFECT IN TORSION GRAVITY(Editura Acad Romane, 2014) Salti, M.; Acikgoz, I.The spin precession of a Dirac particle in monotonically increasingly boosted coordinates is calculated using torsion gravity (teleparallel theory of gravity). Also, we find the vector and the axial-vector parts of the torsion tensor.Öğe Polytropic Gas and Gravitational Thermodynamics(Elsevier, 2014) Salti, M.; Acikgoz, I.; Abedi, H.We mainly assume that our universe is locally rotationally symmetric (LRS) Bianchitype II and is filled with a combination of a polytropic gas and baryonic matter. Also, we consider the polytropic gas scenario as the unification of dark matter and dark energy. By making use of these assumptions, we investigate the first and second laws of gravitational thermodynamics on the apparent horizon.Öğe SPIN-1/2 PARTICLES IN TORSION GRAVITY WHEN A CONSTANT ELECTRIC FIELD IS PRESENT(Editura Acad Romane, 2013) Keskin, A. I.; Binbay, F.; Salti, M.; Acikgoz, I.In this work, we focus on the dynamics of Dirac particles in the presence of a constant electric field in a cosmological anisotropic universe. Instead of Einstein's theory of general relativity, we perform the calculations using the teleparallel theory of gravity which is also called as the torsion gravity. First, we found the exact solution of the teleparallel Dirac equation in an anisotropic Bianchi-I universe. Second, the harmonic oscillator behaviour of the solution and then the quantization of oscillation frequency had been discussed. Third, we investigated the spin precession of Dirac particles and dispute the axial-vector spin coupling term.Öğe Thermodynamics of Chaplygin Gas Interacting with Cold Dark Matter(Springer/Plenum Publishers, 2013) Salti, M.The main goal of the present work is to investigate the validity of the second law of gravitational thermodynamics in an expanding Godel-type universe filled with generalized Chaplygin gas interacting with cold dark matter. By assuming the Universe as a thermodynamical system bounded by the apparent horizon, and calculating separately the entropy variation for generalized Chaplygin gas, cold dark matter and for the horizon itself, we obtained an expression for the time derivative of the total entropy. We conclude that the 2nd law of gravitational thermodynamics is conditionally valid in the cosmological scenario where the generalized Chaplygin gas interacts with cold dark matter.
