Yazar "Baysal, H." seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • [ X ]
    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.
  • [ X ]
    Öğe
    Five-dimensional cosmological model with variable G and ?
    (Iop Publishing Ltd, 2007) Baysal, H.; Yilmaz, I.
    Eintein's field equations with G and Lambda both varying with time are considered in the presence of a perfect fluid for five-dimensional cosmological model in a way which conserves the energy momentum tensor of the matter content. Several sets of explicit solutions in the five-dimensional Kaluza-Klein type cosmological models G and Lambda are obtained. The diminishment of extra dimension with the evolution of the universe for the five-dimenonal model is exhibited. The physical properties of the model is exhibited. The physical properties of the models are examined.
  • [ X ]
    Öğe
    Moller energy-momentum complex in general relativity for higher dimensional universes
    (Iop Publishing Ltd, 2007) Ayguen, M.; Ayguen, S.; Yilmaz, I.; Baysal, H.; Tarhan, I.
    Using the Moller energy momentum definition in general relativity (GR) we calculate the total energy momentum distribution associated with (n + 2)-dimensional homogeneous and isotropic model of the universe. It is found that total energy of Moller is vanishing in (n + 2) dimensions everywhere but n-momentum components of Moller in (n + 2) dimensions are different from zero. Also, we evaluate the static Einstein Universe, FRW universe and de Sitter universe in four dimensions by using (n + 2)-type -metric, then calculate the Moller energy momentum distribution of these spacetimes. However, our results are consistent with the results of Banerjee and Sen, Xulu, Radinschi, Vargas, Cooperstock-Israelit, Aygun et at., Rosen, and Johri et al. in four dimensions.
  • Küçük Resim
    Öğe
    Observational constraints on the cubic parametrization of the deceleration parameter in f(R, T) gravity
    (Springer Science and Business Media Deutschland GmbH, 2023) Baysal, H.; Sofuoğlu, D.; Tiwari, R. K.
    In this paper, we consider the cubic parametrization of the deceleration parameter, in f(R, T) theory of gravitation, where R is the Ricci scalar and T is the trace of the energy–momentum tensor of matter for investigating the expansion history of the universe in the context of flat FRW universe. We use H(z) and SNIa from Union 2.1 compilation datasets with 57 and 580 data points, respectively, in order to obtain the best fit values of the model parameters and the Hubble constant. After constructing the model and solving the modified field equations, by using the best fit values of the parameters, we represent the physical and geometrical properties of the model numerically and discuss their evolution in detail. We show that the model starts with an initial singularity and will have a big rip singularity in the near future. We also show that the model of the universe has evolved from an initial matter-dominated period to one in which it is dominated by dark energy which exhibits behaviour of quintessence currently and phantom in the future.
  • [ X ]
    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.
  • [ X ]
    Öğe
    Reply to comments on 'Five-dimensional cosmological model with variable g and ?'
    (Iop Publishing Ltd, 2008) Baysal, H.; Yilmaz, I.
    The results of ours are correct. There are misprints in the sign of Eq. (11) and the factor (n - 1) in Eq. (12) in our paper [Chin. Phys. Lett. 24 (2007) 2185]. We did not study special values of n = 1 and n = -3.