Yazar "Salti, Mustafa" seçeneğine göre listele

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    Black holes, wormholes and the Hamiltonian approach in the framework of teleparallel gravity
    (Iop Publishing Ltd, 2013) Salti, Mustafa; Acikgoz, Irfan
    In order to elaborate the conserved energy distribution (due to matter and fields including gravity) associated with some black hole and wormhole models we investigate a general space-time in the framework of teleparallel gravity using the Hamiltonian approach. After performing the calculations to obtain the energy distributions generally, we consider four different specific space-times (two of which are black holes and the others are wormholes). Since, the general relativity versions of the calculations for the Vaidya black holes and conformal scalar dyon black holes have been done previously in the literature, we compare our results with both. We see that the results are the same and agree with each other. In this way, the calculations give consistency with the results of different formulations, both in general relativity and teleparallel gravity.
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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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    Dynamics of light in teleparallel bianchi-type i universe
    (Institute of Physics Publishing, 2014) Salti, Mustafa
    In the present study, using the Fourier analysis method and considering the Bianchi-type I spacetime, we investigate the dynamics of photon in the torsion gravity, and show that the free-space Maxwell equations give the same results. Furthermore, we also discuss the harmonic oscillator behavior of the solutions.
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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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    f(T,R) theory of gravity
    (World Scientific Publ Co Pte Ltd, 2018) Salti, Mustafa; Korunur, Murat; Acikgoz, Irfan; Pirinccioglu, Nurettin; Binbay, Figen
    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.
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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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    Ghost quintessence in fractal gravity
    (Indian Acad Sciences, 2015) Abedi, Habib; Salti, Mustafa
    In this study, using the time-like fractal theory of gravity, we mainly focus on the ghost dark energy model which was recently suggested to explain the present acceleration of the cosmic expansion. Next, we establish a connection between the quintessence scalar field and fractal ghost dark energy density. This correspondence allows us to reconstruct the potential and the dynamics of a fractal canonical scalar field (the fractal quintessence) according to the evolution of ghost dark energy density.
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    Godel-type spacetimes in f(R)-gravity
    (De Gruyter Poland Sp Z O O, 2013) Salti, Mustafa; Korunur, Murat; Acikgoz, Irfan
    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 Godel-type metrics. We also take into account five popular f(R) models to obtain specific results.
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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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    Reconstruction of ghost scalar fields
    (Springer Heidelberg, 2014) Salti, Mustafa
    In the literature, a large number of approaches have been done to reconstruct the potential and dynamics of the scalar fields by establishing a connection between holographic/Ricci/new agegraphic/ghost energy density and a scalar field model of dark energy. In most of these attempts, the analytical form of the potentials in terms of the scalar field have not been reconstructed due to the complexity of the equations involved. In the present work, we establish a correspondence between ghost dark energy and quintessence, tachyon and dilaton scalar field models in anisotropic Bianchi type-I universe to reconstruct the dynamics of these scalar fields
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    THERMODYNAMICS IN f (T, ?) GRAVITY
    (Editura Acad Romane, 2015) Askin, Muzaffer; Abedi, Habib; Salti, Mustafa
    In the present study, we discuss a non-equilibrium picture of thermodynamics at the apparent horizon of flat Friedmann-Roberton-Walker universe in f(T,theta) theory of gravity, where T is the torsion scalar and theta is the trace of the energy-momentum tensor. Mainly, we investigate the validity of the first and second laws of thermodynamics in this scenario. We consider two descriptions of the energy-momentum tensor of dark energy density and pressure and discuss that an equilibrium picture of gravitational thermodynamics can not be given in both cases. Furthermore, we also conclude that the second law of gravitational thermodynamics can be achieved both in phantom and quintessence phases of the universe.