Yazar "Aygun, Sezgin" seçeneğine göre listele

Listeleniyor 1 - 19 / 19
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    Bianchi type-I Universe in f(R, T) Modified Gravity with Quark Matter and A
    (Amer Inst Physics, 2017) Caglar, Halife; Aygun, Sezgin
    In this study, we investigate homogeneous and anisotropic Bianchi type I universe in the presence of quark matter source in f (R, T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011) with cosmological constant A (where R is the Ricci scalar and T is the trace of the energy momentum tensor). For this aim we have used the anisotropy feature of Bianchi type I universe and equation of states (EoS) of quark matter. We explore the exact solution f(R, T)=R + 2f(T) model for Bianchi type I universe model. When t -> infinity, we get very small cosmological constant value, this result agrees with recent observations.
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    Energy and momentum of Rigidly Rotating Wormhole space-time
    (Wydawnictwo Uniwersytetu Jagiellonskiego, 2006) Aygun, Melis; Yilmaz, Ihsan; Aygun, Sezgin
    This study is purposed to elaborate the problem of energy and momentum distribution of the Rigidly Rotating Wormhole space-time in general theory of relativity. In this connection, we use the energy-momentum definitions of Einstein, Bergmann-Thomson and Tolman. We obtained that the energy and momentum distributions of Einstein, Bergmann-Thomson and Tolman definitions give the same results in Rigidly Rotating Wormhole space-time.
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    Energy distributions in Szekeres type I and II space-times
    (Polish Acad Sciences Inst Physics, 2006) Aygun, Sezgin; Aygun, Melis; Tarhan, Ismail
    In this study, in context of general relativity we consider Einstein, Bergmann-Thomson, Moller and Landau-Lifshitz energy-momentum definitions and we compute the total energy distribution (due to matter and fields including gravitation) of the universe based on Szekeres class I and class II space-times. We show that Einstein and Bergmann-Thomson definitions of the energy-momentum complexes give the same results, while Moller's and Landau-Lifshitz's energy-momentum definition does not provide same results for Szekeres class II space. The definitions of Einstein, Bergmann-Thomson and Moller definitions of the energy-momentum complexes give similar results in Szekeres class I space-time.
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    Energy distributions of Bianchi type-VIh Universe in general relativity and teleparallel gravity
    (Indian Acad Sciences, 2017) Ozkurt, Seref; Aygun, Sezgin
    In this paper, we have investigated the energy and momentum density distributions for the inhomogeneous generalizations of homogeneous Bianchi type-VIh metricwith Einstein, Bergmann-Thomson, Landau-Lifshitz, Papapetrou, Tolman and Moller prescriptions in general relativity (GR) and teleparallel gravity (TG). We have found exactly the same results for Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum distributions in Bianchi type-VIh metric for different gravitation theories. The energy-momentum distributions of the Bianchi type-VIh metric are found to be zero for h = -1 in GR and TG. However, our results agree with Tripathy et al, Tryon, Rosen and Aygun et al.
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    Energy Momentum Distributions of Monopole Metric in Teleparallel Gravity
    (Amer Inst Physics, 2017) Aygun, Sezgin
    In this study, we investigate energy and momentum distributions of Monopole metric. For this purpose, we have used Einstein, Bergmann-Thomson and Landau-Lifshitz energy and momentum densities in Teleparallel Gravity (TG). We obtained that: (i) The solutions of Einstein and Bergmann-Thomson energy and momentum distributions give the same results but Landau-Lifshitz energy distribution does not provide same results in TG. (ii) The momentum densities of Einstein, Bergmann-Thomson and Landau-Lifshitz are vanish in TG for monopole metric. (hi) The obtained energy-momentum solutions are different from the earlier results in General Relativity (GR).
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    Energy Momentum Distributions of Texture and Monopole Metrics in General Relativity
    (Springer/Plenum Publishers, 2010) Aygun, Sezgin
    The aim of this study is to investigate the energy-momentum distributions of texture and monopole topological defects metrics in general relativity (GR). For this aim Einstein, Bergmann-Thomson, Landau-Lifshitz (LL), Moller and Papapetrou energy-momentum densities have been used in general relativity theory. We obtained that (i) for the texture metric only Einstein and Bergmann-Thomson energy densities give the same results but the others energy and momentum densities do not provide the same results in GR; (ii) for the monopole metric, while Einstein, Bergmann-Thomson and Papapetrou energy and momentum densities are giving the same energy-momentum results, Moller and Landau-Lifshitz densities do not give the same energy results with the other definitions in GR.
  • Küçük Resim
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    Energy-momentum localization for Bianchi type-IV Universe in general relativity and teleparallel gravity
    (Indian Acad Sciences, 2012) Aygun, Sezgin; Tarhan, İsmail
    In this study we have investigated the energy-momentum distributions for homogeneous and an isotropic Bianchi type-IV in B class Universe. For this purpose, we have used energy-momentum complexes of Einstein, Bergmann-Thomson, Landau-Lifshitz (LL), Papapetrou, Tolman and Moller in general relativity (GR) as also Einstein, Bergmann-Thomson, Landau-Lifshitz and Moller in teleparallel gravity (TG). From the obtained results we have found that Einstein and Bergmann-Thomson distributions are exactly giving the same results in GR and TO but the Landau-Lifshitz, Papapetrou Tolman and Moller energy-momentum distributions do not provide the same results with Einstein and Bergmann-Thomson in OR and TG. Furthermore, Einstein, Bergmann-Thomson and LL results are the same in different gravitation theories and we get that both OR and TG are equivalent theories for these prescriptions. From the obtained solutions, we could say that these are equivalent theories. Also, Moller energy-momentum distributions do not give the same results in OR and TG. However, we have found that all energy prescriptions are negative and our results agree with Nester et al.
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    Exact Solutions of Bulk Viscous With String Cloud Attached to Strange Quark Matter For Higher Dimensional FRW Universe in Lyra Geometry
    (Amer Inst Physics, 2016) Caglar, Halife; Aygun, Sezgin
    In this study, we have investigated bulk viscous with strange quark matter attached to the string cloud for higher dimensional Friedman-Robertson-Walker (FRW) universe in Lyra geometry. By using varying deceleration parameter and conservation equations we have solved Einstein Field Equations (EFE's) and obtained generalized exact solutions for our model. Also we have found that string is not survived for bulk viscous with strange quark matter attached to the string cloud in framework higher dimensional FRW universe in Lyra geometry. This result agrees with Kiran and Reddy, Krori et al, Sahoo and Mishra and Mohanty et al. in four and five dimensions.
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    Higher Dimensional FRW Universe Solutions in Creation Field Cosmology
    (Amer Inst Physics, 2017) Caglar, Halife; Aygun, Sezgin
    In this study, we investigate the solutions of higher dimensional Friedmann-Robertson-Walker (FRW) universe in Creation Field Cosmology (CFC) when strange quark matter (SQM) and normal matter (NM) attached to the string cloud and domain walls. Using deceleration parameter, we get two different solutions in CFC. Also, we obtain zero string tension density (rho(s) = 0) for SQM attached to the string cloud. We get constant creation field function C for SQM and normal matter attached to domain walls. Also, the features of obtained solutions are generalized and discussed.
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    Higher-dimensional energy-momentum problem for Bianchi types V and I universes in gravitation theories
    (World Scientific Publ Co Pte Ltd, 2015) Kiy, Guliz; Aygun, Sezgin
    Using the Einstein, Bergmann-Thomson, Landau-Lifshitz, Moller, Papapetrou and Tolman energy-momentum complexes in general relativity (GR) and teleparallel gravity (TG), we calculate the total energy-momentum distributions associated with N-dimensional Bianchi type V universe. While the solutions of Einstein, Bergmann-Thomson and Tolman energy and momentum densities are the same as each other, the solutions of Landau-Lifshitz, Moller and Papapetrou energy-momentum densities are different for N-dimensional Bianchi type V space-time in GR and TG. Obtained results for Einstein, Bergmann-Thomson and Landau-Lifshitz definitions we could say that GR and TG are in the same class. Because different energy-momentum distributions provide same results. However we have discussed N-dimensional Bianchi type I solutions and then we obtained all energy-momentum solutions are vanish in GR and TG theories. These results agree with Banerjee-Sen, Xulu, Aydogdu-Salti and Radinschi in four dimensions.
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    Investigation of dark energy scenarios in f(Q) gravitation theory
    (World Scientific Publ Co Pte Ltd, 2024) Jalali, Samira; Aygun, Sezgin
    In order to solve the mystery of the accelerating and expanding universe model first, various dark energy candidates, such as Quintessence, Tachyon, k-essence, Phantom and DBI-essence, were investigated in detail in the f(Q) modified symmetric teleparallel gravitation theory for homogeneous and isotropic FRLW universe model. The f(Q) = aQ(n )+ b model is used to obtain solutions in f(Q) theory. Also, the physical behaviors of some cosmological parameters such as pressure and density were studied. Dark energy candidates were analyzed for different values of n with various graphs.
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    Magnetized strange quark matter in f(R, T) gravity with bilinear and special form of time varying deceleration parameter
    (Elsevier Science Bv, 2018) Sahoo, P. K.; Sahoo, Parbati; Bishi, Binaya K.; Aygun, Sezgin
    In this paper, we have studied homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type-I model with magnetized strange quark matter (MSQM) distribution and cosmological constant A in f(R, T) gravity where R is the Ricci scalar and T the trace of matter source. The exact solutions of the field equations are obtained under bilinear and special form of time varying deceleration parameter (DP). Firstly, we have considered two specific forms of bilinear DP with a single parameter of the form: q = alpha(1-t/1+t) and q = -alpha t/1+t, which leads to the constant or linear nature of the function based on the constant a. Second one is the special form of the DP as q = -1 + beta/1+a(beta) From the results obtained here, one can observe that in the early universe magnetic flux has more effects and it reduces gradually in the later stage. For t -> infinity, we get p -> -Bc, and p -> B-c. The behaviour of strange quark matter along with magnetic epoch gives an idea of accelerated expansion of the universe as per the observations of the type Ia Supernovae.
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    Marder type universe with bulk viscous string cosmological model in f (R,T) gravity
    (Tubitak Scientific & Technological Research Council Turkey, 2017) Aygun, Sezgin
    In this study, we have investigated homogeneous and anisotropic Marder space-time with bulk viscous string matter distribution in f (R,T) gravity. For this aim we have used the anisotropy feature (sigma(x)(x)/theta) of Marder space-time and a deceleration parameter in two different f (R,T) models. We have obtained bulk viscous matter distribution solutions in f (R,T) gravity. Finally, some kinematical and physical properties are discussed.
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    Non-existence of Brans-Dicke theory in higher dimensional FRW universe
    (Springer, 2016) Caglar, Halife; Aygun, Sezgin
    In this paper, we have studied exact solutions of Brans-Dicke (BD) theory for higher dimensional generalized Friedmann-Robertson-Walker (FRW) universe in the presence of strange quark matter (SQM) attached to the string cloud and domain walls. We have obtained that string tension density does not survive in this model. This result agrees with Kiran and Reddy, Krori et al., Sahoo and Mishra and Reddy. Also we have obtained constant scalar field in the presence of string cloud and domain walls. Then BD theory does not observe for higher dimensional FRW universe with SQM attached to the string cloud and domain walls. Our BD solutions turn into general relativity (GR). Finally, some physical properties are discussed.
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    Ruban Universe Model Solutions with Scalar Field in f(R, T) Gravity
    (Springer Int Publ Ag, 2024) Aygun, Sezgin; Aktas, Arzu
    In this study, normal, phantom scalar fields (SF) and massive scalar field (MSF) solutions were investigated in f(R,T) andGeneral Relativity theories (GRT) for inhomogeneous and anisotropic Ruban space-time, which is believed to represent thefirst moments of the universe. Solutions were obtained by using the A(x,t)=(xB(t))(n) relation between the metricpotentials of the Ruban universe and the scalar potential models V(phi)=V-0 and V(phi)=V(0)e-(a phi(t)). Obtained results aresupported by graphics. The solutions obtained for scalar fields are compatible with the studies of Aygu n (Gravit Cosmol24:302-307, 2018) and Singh and Singh (Astrophys Space Sci 356:153-162, 2015).
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    Scalar field solutions for anisotropic universe models in various gravitation theories
    (World Scientific Publ Co Pte Ltd, 2020) Kabak, Ali; Aygun, Sezgin
    In this study, we have investigated homogeneous and anisotropic Marder and Bianchi type I universe models filled with normal and phantom scalar field matter distributions with. in f(R, T) gravitation theory (T. Harko et al., Phys. Rev. D 84 (2011) 024020). In this model, R is the Ricci scalar and T is the trace of energy-momentum tensor. To obtain exact solutions of modified field equations, we have used anisotropy feature of the universe and different scalar potential models with f(R, T) = R + 2f(T) function. Also, we have obtained general relativity (GR) solutions for normal and phantom scalar field matter distributions in Marder and Bianchi type I universes. Additionally, we obtained the same scalar function values by using different scalar field potentials for Marder and Bianchi type I universe models with constant difference in f(R, T) gravity and GR theory. From obtained solutions, we get negative cosmological term value for V(phi) = V-0 constant scalar potential model with Marder and Bianchi type I universes in GR theory. These results agree with the studies of Maeda and Ohta, Aktas et al. also Biswas and Mazumdar. Finally, we have discussed and compared our results in gravitation theories.
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    Scalar field theory and energy-momentum problem of Yilmaz-Rosen metric in general relativity and teleparallel gravity
    (Springer, 2008) Aygun, Sezgin; Tarhan, Ismail; Baysal, Huesnue
    In this paper, using the energy momentum definitions of the Einstein, Bergmann-Thomson, Landau-Lifshitz and Moller in general relativity (GR) and teleparallel gravity (TG), we have evaluated the energy-momentum distributions of Yilmaz-Rosen metric. We have obtained that these different energy-momentum definitions give different results in GR and TG. Furthermore these results are same in different gravitation theories and we get that both general relativity and teleparallel gravity are equivalent theories for Einstein, Bergmann-Thomson and Landau-Lifshitz prescriptions. Also, while the Moller energy definitions are same and zero but the momentum prescriptions are disagree in GR and TG.
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    String cloud and domain walls with quark matter for a higher dimensional FRW universe in self creation cosmology
    (Chinese Physical Soc, 2016) Caglar, Halife; Aygun, Sezgin
    In this study, we research a higher dimensional flat Friedmann-Robertson-Walker (FRW) universe in Barber's second theory when strange quark matter (SQM) and normal matter (NM) are attached to the string cloud and domain walls. We obtain zero string tension density for this model. We obtain dust quark matter solutions. This result agrees with Kiran and Reddy, Krori et al, Sahoo and Mishra and Reddy. In our solutions the quark matter transforms to other particles over time. We also obtain two different solutions for domain walls with quark and normal matters by using a deceleration parameter. Also, the features of the obtained solutions are discussed and some physical and kinematical quantities are generalized and discussed. Our results are consistent with Yilmaz, Adcox et al and Back et al in four and five dimensions.
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    Various dark energy models with time-varying G and ? in f(R, T) gravitation theory
    (World Scientific Publ Co Pte Ltd, 2019) Aygun, Sezgin
    In this research, we have investigated tachyon and k-essence dark energy (DE) candidates with varying G and Lambda for Marder universe in f(R, T) gravitation theory [Harko et al., Phys. Rev. D 84, 024020 (2011)]. Here, f(R, T) is the arbitrary function of Ricci scalar (R) and the trace of T-ik. To solve f(R, T) gravity field equations, three different approximations have been used such as cosmological term, equation of state (EoS) parameter and the anisotropy feature of Marder universe. Also, we have discussed some physical results with various graphics.