Yazar "Aydogdu, Oktay" seçeneğine göre listele

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    Brane-world black holes and energy-momentum vector
    (Springer, 2006) Salti, Mustafa; Aydogdu, Oktay; Korunur, Murat
    The Brane-World black hole models are investigated to evaluate their relative energy and momentum components. We consider Einstein and Moller's energy-momentum prescriptions in general relativity, and also perform the calculation of energy-momentum density in Moller's 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 Moller's 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.
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    Brans Dicke type teleparallel scalar-tensor theory
    (World Scientific Publ Co Pte Ltd, 2017) Salti, Mustafa; Aydogdu, Oktay; Yanar, Hilmi; Binbay, Figen
    The teleparallel alternative of general relativity which is based on torsion instead of curvature is considered as the gravitational sector to explore the dark universe. Inspired from the well-known Brans-Dicke gravity, here, we introduce a new proposal for the galactic dark energy effect. The new model includes a scalar field with self-interacting potential and a non-minimal coupling between the gravity and scalar field. Additionally, we analyze the idea via the Noether symmetry approach and thermodynamics.
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    Energy associated with the Gibbons-Maeda dilaton spacetime
    (Springer/Plenum Publishers, 2006) Aydogdu, Oktay; Salti, Mustafa; Korunur, Murat; Acikgoz, Irfan
    In order to obtain energy and momentum (due to matter and fields including gravitation) distributions of the Gibbons-Maeda dilaton spacetime, we use the Moller 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 Moller 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 Moller.
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    Extended scalar-tensor theory and thermodynamics in teleparallel framework
    (World Scientific Publ Co Pte Ltd, 2016) Salti, Mustafa; Aydogdu, Oktay; Acikgoz, Irfan
    We present here a new modified gravitation theory for the galactic dark energy effect by using a general Lagrangian density which is represented by an arbitrary function f(T, phi, X) where T describes the torsion scalar in teleparallel gravity while X shows the kinetic scalar field energy. While the function is in general form, once reduced, the model can be transformed into some of the other well-known gravitation theories. After deriving the corresponding field equations and considering the flat Friedmann-Robertson-Walker type universe which is filled with ordinary cosmic matter, we discuss both the non-equilibrium and equilibrium profiles of galactic thermodynamics. We find that there exists an equilibrium picture of thermodynamics. Additionally, we also generalize ordinary f(T, phi, X) model's action to the case in which there exists an interaction between the chameleon and scalar fields.
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    Galactic entropy in extended Kaluza-Klein cosmology
    (World Scientific Publ Co Pte Ltd, 2016) Yanar, Hilmi; Salti, Mustafa; Aydogdu, Oktay; Acikgoz, Irfan; Yasar, Erol
    We use a Kaluza-Klein model with variable cosmological and gravitational terms to discuss the nature of galactic entropy function. For this purpose, we assume a universe filled with dark fluid and consider five-dimensional (5D) field equations using the Gamma law equation. We mainly discuss the validity of the first and generalized second laws of galactic thermodynamics for viable Kaluza-Klein models.
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    Holographic scalar fields in Kaluza-Klein framework
    (Springer Heidelberg, 2017) Erkan, Sevda; Pirinccioglu, Nurettin; Salti, Mustafa; Aydogdu, Oktay
    Making use of the Friedmann-Robertson-Walker (FRW) type Kaluza-Klein universe (KKU), we discuss the holographic dark energy density (HDED) in order to develop its correspondence with some scalar field descriptions such as the tachyon, quintessence, DBI-essence, dilaton and the k-essence. It is concluded that the Kaluza-Klein-type HDED proposal becomes stable throughout the history of our universe and is consistent with the current status of the universe. Next, we obtain the exact solutions of self-interacting potential and scalar field function for the selected models.
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    The Lukash plane-wave attractor and relative energy
    (World Scientific Publ Co Pte Ltd, 2007) Korunur, Murat; Salti, Mustafa; Aydogdu, Oktay
    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 VII delta 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 omega = 1 and Xi(2) = 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. Furthermore, our results support the hypothesis by Cooperstock that the energy is confined to the region of nonvanishing energy momentum tensor of matter and all non-gravitational fields, and also sustain the importance of the energy momentum definitions in the evaluation of the energy distribution associated with a given spacetime.
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    Moller's four-momentum of electric and magnetic black holes
    (Springer/Plenum Publishers, 2007) Binbay, Figen; Pirinccioglu, Nurettin; Salti, Mustafa; Aydogdu, Oktay
    In order to evaluate energy and momentum components associated with two different black hole models, i.e. the electric and magnetic black holes, we use the Moller energy-momentum prescriptions both in Einstein's theory of general relativity and the teleparallel gravity. We obtain the same energy and momentum distributions in both of these different gravitation theories. The energy distribution of the electric black hole depends on the mass M and the magnetic black hole energy distribution depends on the mass M and charge Q. In the process, we notice that (a) the energy obtained in teleparallel gravity is also independent of the teleparallel dimensionless coupling parameter, which means that it is valid not only in teleparallel equivalent of general relativity but also in any teleparallel model, (b) our results also sustains the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given spacetime, and (c) the results obtained support the viewpoint of Lessner that the Moller energy-momentum complex is a powerful concept of energy and momentum.
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    Topological black holes and momentum four-vector
    (World Scientific Publ Co Pte Ltd, 2007) Pirinccioglu, Nurettin; Binbay, Figen; Acikgoz, Irfan; Aydogdu, Oktay
    We consider the energy momentum definition of the Moller in both general relativity and teleparallel gravity to evaluate the energy distribution (due to both matter and fields including gravitation) associated with the topological black holes with a conformally coupled scalar field. Our results show that the energy depends on the mass M and charge Q of the black holes and cosmological constant Lambda. In some special limits, the expression of the energy reduces to the energy of the well-known spacetimes. The results also support the viewpoint of Lessner that the Moller energy momentum formulation is a powerful concept of the energy momentum. Furthermore, the energy obtained in teleparallel gravity is also independent of the teleparallel dimensionless coupling constants which means that it is valid not only in the teleparallel equivalent of the general relativity but also in any teleparallel model.