Matematik Bölümü Koleksiyonu

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https://hdl.handle.net/20.500.12428/2241

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Magnetized strange quark matter in reconstructed f(R, T) gravity for Bianchi I and V universes with cosmological constant
(Tubitak Scientific & Technological Research Council Turkey, 2017) Aktaş, Can
In this article, we have investigated the behaviors of magnetized strange quark matter distributions for Bianchi I and V universes in reconstructed f (R, T) = α1R+α2f3(T) gravity (here α1 and α2 are constants; f3(T) is an arbitrary function of T). To get solutions of the field equations we have used a deceleration parameter and the equation of state for strange quark matter. The new represented f(R,T) model includes two models of Harko et al. and transforms to general relativity. When t → ∞, we get the dark energy model (p = −ρ) in reconstructed f (R, T) = α1R + α2f3(T) gravity. However, we obtain zero magnetic field in all f(R, T) gravitation models.
Quark and strange quark matter in f(R) gravity for Bianchi type I and V space-times
(Springer/Plenum Publishers, 2012) Yılmaz, İhsan; Baysal, Hüsnü; Aktaş, Can
Behaviors of quark matter and strange quark matter which exist in the first seconds of the early Universe in f(R) gravity are studied for Bianchi I and V universes. In this respect, we obtain exact solutions of the modified Einstein field equations by using anisotropy feature of Bianchi I and V space-times. In particular, we investigate exact f(R) functions for Bianchi I as the contribution of strange quark and quark matter. Also, we have concluded that quark matter may contribute to the early acceleration of the universe since quark matter behaves like phantom-type dark energy. Furthermore, obtained f(R) solutions represents early eras of the Universe since f(R) solutions for quark matter coincide with f(R) equations for inflation. From this point, we can reach the conclusion that quarks may be source of the early dark energy of the universe or source of little inflation due to their repulsive force.
Domain wall solutions with quark matter in higher dimensional space-times
(Amer Inst Physics, 2007) Aktaş, Can; Yılmaz, İhsan; Baysal, Hüsnü; Aygün, Melis; Demirel, Canan
In this paper, we have examined quark matter in the perfect form attached to domain walls in the higher dimensional spherical symmetric space-time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for higher dimensional spherical symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.
Strange quark matter solutions for Marder's universe in f (R, T) gravity with Λ
(Springer, 2016) Aygün, Sezgin; Aktaş, Can; Yılmaz, İhsan
In this paper, we investigate homogeneous cylindrically symmetric Marder's universe in the presence of strange quark matter (SQM) source in f (R, T) gravity with cosmological constant Lambda. For this aim we have used the anisotropy feature (sigma(x)(x)/theta) of Marder type universe and equation of state (EoS) strange quark matter to obtain solutions in two classes f (R, T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011). Finally, some physical and kinematical properties are discussed.
Quark and strange quark matter solutions for higher dimensional FRW universe in Lyra geometry
(Springer Heidelberg, 2015) Aygün, Sezgin; Çağlar, Halife; Taşer, Doğukan; Aktaş, Can
In this study, we have investigated the higher dimensional flat Friedmann-Robertson-Walker (FRW) universe for a cloud of string with perfect fluid attached quark and strange quark matter (SQM) in Lyra geometry. Generalized (n + 2) dimensional flat FRW universe solutions have been achieved with the aid of equation of states (EOS) and deceleration parameter (q). From the field equations, we have obtained that the cloud of string with perfect fluid does not survive. Since the string tension density vanishes (lambda = 0) for this model, as a result, the cloud of string with perfect-fluid-attached quark and strange quark matter energy-momentum tensor is automatically transformed into a perfect-fluid-attached quark and strange quark matter energy-momentum tensor. Also, our solutions agree with Halford's study. beta(2) behaves like a cosmological constant. When t -> infinity the pressure of quark matter and the density go to zero, then, the quark matter transforms into another matter with time. Also our quark matter solutions are in agreement with the present idea.
Magnetized strange quark matter solutions in f(R, T) gravity with cosmological constant
(Elsevier Science Bv, 2017) Aktaş, Can; Aygün, Sezgin
In this research, we have studied magnetized strange quark matter (SQM) solutions for Friedmann-Robertson-Walker (FRW) universe in f(R, T) gravity. To obtain exact solutions of modified field equations we have used f(R, T) = R + 2 f(T) and f(R, T) = f(1)(R) + f(2)(T) models given by Harko et al. (Harko et al. in Phys. Rev. D 84: 024020, 2011) and f(R, T) = R + f(3)(T) model (here f(3) is an arbitrary function) with cosmological constant Lambda. For t -> 8 we obtain p = -rho dark energy situation with small constant values of cosmological constant in three different f (R, T) gravitation models. In our solutions magnetic field does not observe also we have transformed our solutions from FRW universe to Static Einstein Universe (SEU) and we get f(R, T) gravity results for SEU universe. Finally we discussed our physical solutions. (C) 2016 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.
Relationship between magnetic field and anisotropy parameter in gravitation theories
(World Scientific Publ Co Pte Ltd, 2018) Aktaş, Can; Aygün, Sezgin; Sahoo, Pradyumn Kumar
The magnetized strange quark matter (MSQM) solutions are obtained for a Marder type universe using constant deceleration parameter. The exact solutions of field equations are obtained for f(R,T) = R 2f(T) model given by [T. Harko et al., Phys. Rev. D 84, 024020 (2011)] with cosmological term. Also, we have obtained General Relativity (GR) solutions for MSQM distributions. For t -> infinity, we get the dark energy model, i.e. p -> -B-c, rho -> B-c and omega = -1. However, for t -> infinity, we find the cosmological constant A as negative in f (R, T) theory and GR. These results agree with [S. Aygun et al., Astrophys. Space Sci. 361, 380 (2016); C. Aktas and S. Aygun, Chinese T. Phys. 55, 71 (2017); P. K. Sahoo et al., Mod. Phys. Lett. A 32, 1750105 (2017)] in f(R,T) theory. The physical consequences of our obtained models are discussed at the end.
Magnetized quark and strange quark matter in the spherical symmetric space-time admitting conformal motion
(Springer/Plenum Publishers, 2007) Aktaş, Can; Yılmaz, İhsan
In this paper, we have examined magnetized quark and strange quark matter in the spherical symmetric space-time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for spherical symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.
Does magnetized strange quark matter exist in the early universe?
(World Scientific Publ Co Pte Ltd, 2022) Kalkan, Sinem; Aktaş, Can; Aygün, Sezgin
In this paper, we have examined the magnetized strange quark matter (MSQM) distribution in the inhomogeneous anisotropic Einstein-Rosen universe model within the framework of f(R,T) theory and General Relativity (GR) in order to investigate whether there was a magnetic field in the first moments of the universe. With the help of the arbitrary F(r) function, we researched for solutions in both theories for various cases. We have seen that the cubic function F(r) = r(3) gives meaningful results in both theories. We have obtained magnetic field-free strange quark matter solutions for the quadratic and constant states of the arbitrary function F(r). It is seen that the choice of geometry (selection of the F(r) function) has an effect on the presence of the magnetic field. Finally, the physical results are examined on 3D graph.
Non-existence of a massive scalar field for the Marder universe in Lyra and Riemannian geometries
(Elsevier, 2012) Aygün, Sezgin; Aktaş, Can; Yılmaz, İhsan
In this paper, we have studied a massive scalar field for a Marder type universe in the context of Lyra and Riemannian geometries. From the exact solutions obtained we show that the massive scalar field does not survive in Lyra and Riemannian geometries for an anisotropic Marder type universe. Therefore we have solved the massless scalar field problem in Lyra and Riemann geometries for two cases. Also we have obtained vacuum solutions for homogeneous and anisotropic Marder space time in Lyra geometry and the solutions obtained are compared by considering Lyra and Riemann geometries. Finally, some physical and kinematical properties are discussed by using graphics. (C) 2011 Elsevier B.V. All rights reserved.
Behaviors of dark energy and mesonic scalar field for anisotropic universe in f (R) gravity
(Elsevier, 2012) Aktaş, Can; Aygün, Sezgin; Yılmaz, İhsan
In this Letter, we study behaviors of dark energy in the form of perfect fluid and mesonic scalar field for Marder space-time which is anisotropic and homogeneous in f (R) gravity. Exact solutions of the modified Einstein field equations in f (R) gravity are obtained by using anisotropic features, of Marder space-time. We do not make any assumptions about f (R) function while we are solving f (R I equations. We have investigated dark energy behaviors in f (R) gravity. We have concluded that dark energy in our model behaves like phantom type. Also we have concluded that mesonic scalar field transforms to another matters into time. In our solutions, obtained f (R) functions existed by dark energy and mesonic scalar field are same like general one accepted in the literature. Furthermore, physical and kinematical quantities are examined for two matters, separately. Finally obtained solutions are discussed. (C) 2011 Elsevier B.V. All rights reserved.
Scalar Fields for Bianchi-I Model in f(R,T) Theory of Gravity
(Maik Nauka/Interperiodica/Springer, 2024) Kabaoğlu, Yasemin; Aktaş, Can
In physics and cosmology, scalarfields are considered basic. In this study, we are interestedto inspect the conduct of massless scalarfield (SF) and massive scalarfield (MSF) models in f(R, T) theory for Bianchi-I universe models. We discuss two cosmological models with respect to late cosmicacceleration, using constant scalar potential and exponential scalar potential models. Also, we study thebehavior of a massive scalarfield. Finally, we obtain our results in f(R, T)and general relativity (GR). Inaddition, we obtained an LRS Bianchi-I metric as a result of the solutions we made and selection of specialconstants.
Various dark energy models for variables G and Λ in f(R, T) modified theory
(World Scientific Publ Co Pte Ltd, 2019) Aktaş, Can
In this paper, we have researched tachyon field, k-essence and quintessence dark energy (DE) models for Friedmann-Robertson-Walker (FRW) universe with varying G and A in f (R, T) gravitation theory. The theory of f (R, T) is proposed by Harko et al. [Phys. Rev. D 84, 024020, 2011]. In this theory, R is the Ricci scalar and T is the trace of energy-momentum tensor. For the solutions of field equations, we have used linearly varying deceleration parameter (LVDP), the equation of state (EoS) and the ratio between A and Hubble parameter. Also, we have discussed some physical behavior of the models with various graphics.
Anisotropic universe models with magnetized strange quark matter in f(R) gravity theory
(World Scientific Publ Co Pte Ltd, 2020) Özdemir, Onur; Aktaş, Can
In this study, we have investigated generalized anisotropic universe models for magnetized strange quark matter (MSQM) distribution in the framework of f(R) gravitation theory. For this aim, we have used linearly varying deceleration parameter suggested by Akarsu and Dereli (2012) and equation of state for strange quark matter. For LRS Bianchi I universe model, the magnetic field was obtained as zero. But it was found to be different from zero for other universe models. Also, the geometric and physical aspects of the model are discussed in the conclusion.
Quadratic equation of state solutions with Λ in f(R, T) gravitation theory
(Indian Assoc Cultivation Science, 2019) Aygün, Sezgin; Aktaş, Can; Mishra, B.
In this paper, we have investigated the perfect fluid matter distribution with different quadratic equation of states (EoS) parameters in the form (i) p = p(0) + alpha rho + beta rho(2), (ii) p= alpha rho + rho(2)/rho(c) and (iii) p = alpha rho(2) - rho for Marder space-time in f(R,T) theory. The field equations of f(R,T) gravity with the inclusion of cosmological parameter Lambda have been derived for the first case of Harko et al. (Phys Rev D 84(2):024020, 2011) in the form f(R,T)=R + 2f(T). The physical parameters are investigated and its properties are studied.
Behavior of Tsallis holographic dark energy for Marder universe
(World Scientific Publ Co Pte Ltd, 2024) Aktaş, Can
In this study, Tsallis holographic dark energy (THDE) was discussed within the frame of f(R,T) gravitational theory and considering the homogeneous and anisotropic Marder universe. The Hubble horizon was taken into consideration as infrared cutoff of the system. To get the field equations, solutions were used for the THDE density and the anisotropy parameter. Furthermore, a variety of physical parameters such as deceleration parameter, anisotropy parameter and volume have been examined. They have been also been visually examined with the help of graphics. Different values of deceleration parameter consistent with different observational data were mentioned. In addition to this, cosmological parameters like jerk, lerk and snap parameters were analyzed. Statefinder diagnostics which are helpful tools for the separation of dark energy models have been examined. By the calculation and representation of the overall density parameter (Omega) it can be concluded that the anisotropic nature of model vanishes showing a tendency to isotropy in accordance with present universe. Finally, the physical and geometrical nature of the model was studied, collating with relevant studies and observations.
Is the universe homogeneous and isotropic in the time when quark-gluon plasma exists?
(Springer/Plenum Publishers, 2011) Aktaş, Can; Yılmaz, İhsan
In this study, quark and strange quark matter which exist in the first seconds of the early Universe have been studied in the context of general relativity to be able to obtain space-time geometry of first seconds of the early Universe. For this purpose, Einstein's field equations for quark and strange quark matter in the non static spherically symmetric space-time have been solved by using experimental result that anisotropy parameter of quark matter is very small. We have concluded from obtained solutions that the space-time structure of first seconds of the Early Universe is homogeneous and isotropic. Also we have concluded that the color interactions of the quarks may be origin of primordial magnetic field in the early universe.
Investigation of the magnetized string distribution in the Marder universe with the cosmological term in f(R, T) theory
(World Scientific Publ Co Pte Ltd, 2020) Kömürcü, Cihan; Aktaş, Can
In this study, we first obtained the cosmological term naturally in the Einstein-Hilbert type effect for the f (R, T) theory, then we discussed the magnetized string matter in the Marder universe, later the matter Lagrangian is not equivalent to string dust and we calculated independently for the string dust and the electromagnetic field, and added the magnetized string together. Finally, we studied the physical and geometric structure of the universe, limiting our results to some astrophysical observation data.
Energy-momentum distributions of Ruban universe in general relativity and teleparallel gravity
(World Scientific Publ Co Pte Ltd, 2019) Aktaş, Can
In this study, we obtain Einstein, Bergmann-Thomson (BT), Landau-Lifshitz (LL), Moller, Papapetrou (PP) and Tolman energy-momentum (EM) distributions for Ruban universe model in general relativity (GR) and teleparallel gravity (TG). We obtain same results for Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum distributions in GR and TG. Also, we get same results for Einstein and Tolman energy-momentum distributions in GR. The Moller energy-momentum results are different in GR and TG. Also, using Ruban universe model, we obtain LRS Bianchi type I solutions and we get zero energy-momentum results for this universe model in GR and TG. These results of LRS Bianchi type I universe model agree with Aygun et al., Taser et al., Dogru et al., Banerjee-Sen, Tryon and Xulu in different gravitation theories.
Higher dimensional FRW universe solutions with quark and strange quark matter in creation field cosmology
(Elsevier Science Bv, 2016) Aygün, Sezgin; Aktaş, Can; Yılmaz, İhsan; Şahin, Mustafa
In this study, firstly we have studied the behavior of quark and strange quark matter for a (n + 2) -dimensional Friedmann-Robertson-Walker (FRW) universe which is homogeneous and isotropic in creation field (C-field) cosmology. Using the deceleration parameter two different exact solutions of the modified Einstein equations in C-field cosmology are obtained. In addition, we obtain exact solutions of the quark and strange quark matter for a (n + 2)-dimensional homogeneous and isotropic static Einstein universe (SEU) and a maximally symmetric de Sitter vacuum universe in four dimensions. Also, using. C = 0 in C-field theory, we get the SEU and de Sitter vacuum universes in Riemann geometry. Finally, some physical and kinematical quantities are discussed. (C) 2016 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.

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