Yazar "Aygun, S." seçeneğine göre listele
Listeleniyor 1 - 8 / 8
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Bianchi Type-I Universe in Lyra Manifold with Quadratic Equation of State(Amer Inst Physics, 2017) Sen, R.; Aygun, S.In this study, we have solved Einstein field equations for Bianchi type I universe model in Lyra manifold with quadratic equation of state (EoS) p = alpha rho(t)(2) - rho(t). Where alpha not equal 0 is an important constant. Cosmic pressure, density and displacement vector (beta(2)) are related with a constant. In this study beta(2) is a decreasing function of time and behaves like a cosmological constant. These solutions agree with the studies of lialford, Pradhan and Singh, Aygun et al., Agarwal et al., Yadav and liaque as well as SN la observations.Öğe Energy and momentum of Bell-Szekeres space-time in Moller prescription(Polish Acad Sciences Inst Physics, 2007) Aygun, S.This study is purposed to elaborate the problem of energy and momentum distribution of the Bell-Szekeres space time in general theory of relativity. In this connection, we use the energy-momentum definition of Moller and obtain that the energy momentum distributions (due to matter plus field) are vanishing everywhere. This results are exactly the same as viewpoint of Aygun et al. and agree with a previous work of Rosen, Salti et al. and Johri et al. who investigated the problem of the energy in Friedmann-Robertson-Walker universe. The result that the total energy-momentum of the universe in these models are zero support the viewpoint of Tryon.Öğe Energy distributions of the Szekeres universes in teleparallel gravity(Springer/Plenum Publishers, 2008) Aygun, S.; Tarhan, I.; Baysal, H.In order to evaluate the energy distribution (due to matter and fields including gravitation) associated with a space-time model of Szekeres class I and II metrics, we consider the Einstein, Bergmann-Thomson and Landau-Lifshitz energy definitions in the teleparallel gravity (the tetrad theory of gravitation (TG)). We have found that Einstein and Bergmann-Thomson energy distributions give the same results, Landau-Lifshitz distribution is disagree in TG with these definitions. These results are the same as a previous works of Aygun et al., they investigated the same problem by using Einstein, Bergmann-Thomson, Landau-Lifshitz (LL) and Moller energy-momentum complexes in GR. However, both GR and TG are equivalent theories that is the energy densities are the same using different energy-momentum complexes in both theories. Also, our results are support the Cooperstock's hypothesis.Öğe Energy-momentum localization in Marder space-time(Indian Acad Sciences, 2007) Aygun, S.; Aygun, M.; Tarhan, I.Considering the Einstein, Moller, Bergmann-Thomson, Landau-Lifshitz (LL), Papapetrou, Qadir-Sharif and Weinberg's definitions in general relativity, we find the momentum four-vector of the closed Universe based on Marder space-time. The momentum four-vector (due to matter plus field) is found to be zero. These results support the viewpoints of Banerjee-Sen, Xulu and Aydogdu-Salti. Another point is that our study agrees with the previous works of Cooperstock-Israelit, Rosen, Johri et al.Öğe FLRW cosmological models with quark and strange quark matters in f (R, T) gravity(Springer, 2018) Nagpal, Ritika; Singh, J. K.; Aygun, S.In this paper, we have studied the magnetized quark matter (QM) and strange quark matter (SQM) distributions in the presence of f (R, T) gravity in the background of Friedmann-Lemaitre-Robertson-Walker (FLRW) metric. To get exact solutions of modified field equations we have used f (R, T) = R + 2f (T) model given by Harko et al. with two different parametrization of geometrical parameters i.e. the parametrization of the deceleration parameter q, and the scale factor a in hybrid expansion form. Also, we have obtained Einstein Static Universe (ESU) solutions for QM and SQM distributions in f (R, T) gravity and General Relativity (GR). All models in f (R, T) gravity and GR for FRW and ESU Universes with QM also SQM distributions, we get zero magnetic field. These results agree with the solutions of Aktas and Aygun in f (R, T) gravity. However, we have also discussed the physical consequences of our obtained models.Öğe Higher Dimensional Strange Quark Matter Solutions in Self Creation Cosmology(Amer Inst Physics, 2016) Sen, R.; Aygun, S.In this study, we have generalized the higher dimensional flat Friedmann-Robertson-Walker (FRW) universe solutions for a cloud of string with perfect fluid attached strange quark matter (SQM) in Self Creation Cosmology (SCC). We have obtained that the cloud of string with perfect fluid does not survive and the string tension density vanishes for this model. However, we get dark energy model for strange quark matter with positive density and negative pressure in self creation cosmology.Öğe Magnetized strange quark model with Big Rip singularity in f (R, T) gravity(World Scientific Publ Co Pte Ltd, 2017) Sahoo, P. K.; Sahoo, Parbati; Bishi, Binaya K.; Aygun, S.Locally rotationally symmetric (LRS) Bianchi type-I magnetized strange quark matter (SQM) cosmological model has been studied based on f(R, T) gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter, which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model begins with big bang and ends with a Big Rip. The transition of the deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. [Astrophys. T. 835, 26 (2017)]. The well-known Hubble parameter H(z) and distance modulus it(z) are discussed with redshift.Öğe On the energy-momentum problem in static Einstein universe(Iop Publishing Ltd, 2007) Aygun, S.; Tarhan, I.; Baysal, H.The energy-momentum distributions of Einstein's simplest static geometrical model for an isotropic and homogeneous universe are evaluated. For this purpose, Einstein, Bergmann-Thomson, Landau-Lifshitz (LL), Moller and Papapetrou energy-momentum complexes are used in general relativity. While Einstein and Bergmann-Thomson complexes give exactly the same results, LL and Papapetrou energy-momentum complexes do not provide the same energy densities. The Moller energy-momentum density is found to be zero everywhere in Einstein's universe. Also, several spacetimes are the limiting cases considered here.
