Sezgin Aygün

Magnetized strange quark model with Big Rip singularity in f(R, T) gravity

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. J. 835, 26 (2017)]. The well-known Hubble parameter H(z) and distance modulus μ(z) are discussed with redshift.

Energy-momentum localization in Marder space-time

Considering the Einstein, Møller, 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 Aydoġdu-Saltı. Another point is that our study agrees with the previous works of Cooperstock-Israelit, Rosen, Johri et al.

Energy Momentum of Marder Universe in Teleparallel Gravity

Abstract In order to evaluate the energy distribution (due to matter and fields including gravitation) associated with a space-time model of cylindrically-symmetric Marder universe, we consider the Møller, Einstein, Bergmann–Thomson and Landau–Lifshitz energy and momentum definitions in the teleparallel gravity (TG). The energy-momentum distributions are found to be zero. These results are the same as a previous works of Aygün et al., they investigated the same problem in general relativity (GR) by using the Einstein, Møller, Bergmann–Thomson, Landau–Lifshitz (LL), Papapetrou, Qadir–Sharif and Weinberg’s definitions. These results support the viewpoints of Banerjee–Sen, Xulu, Radinschi and Aydoğdu–Saltı. Another point is that our study agree with previous works of Cooperstock–Israelit, Rosen, Johri et al. This paper indicates an important point that these energy-momentum definitions agree with each other not only in general relativity but also in teleparallel gravity. It is also independent of the teleparallel dimensionless coupling constants, which means that it is valid not only in the teleparallel equivalent of general relativity, but also in any teleparallel model.

Magnetized strange quark matter in f(R, T) gravity with bilinear and special form of time varying deceleration parameter

Abstract 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 Λ 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 = α ( 1 − t ) 1 + t and q = − α t 1 + t , which leads to the constant or linear nature of the function based on the constant α. Second one is the special form of the DP as q = − 1 + β 1 + a β . 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 → ∞, we get p → − B c and ρ → Bc. 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.

String cloud and domain walls with quark matter for a higher dimensional FRW universe in self creation cosmology

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.

Topological defect solutions in the spherically symmetric space-time admitting conformal motion

In this paper, we have examined strings with monopole and electric field and domain walls with matter and electric field in the spherically symmetric space-time admitting a one-parameter group of conformal motions. For this purpose, we have solved Einsteins field equations for a spherically symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.

On the Energy-Momentum Problem in Static Einstein Universe

The energy-momentum distributions of Einsteins 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 Einsteins universe. Also, several spacetimes are the limiting cases considered here.

Scalar Field Cosmology in f(R,T) Gravity with Λ

We study the behavior of cosmological parameters, massive and massless scalar fields (normal or phantom) with a scalar potential in f(R, T) theory of gravity for a flat Friedmann-Robertson-Walker (FRW) universe. To get exact solutions to the modified field equations, we use the f(R, T) = R + 2f(T) model by Harko et al. (T. Harko et al., Phys. Rev. D 84, 024020 (2011)), where R is the Ricci scalar and T is the trace of the energy momentum tensor. Our cosmological parameter solutions agree with the recent observational data. Finally, we discuss our results with various graphics.

Energy of Rigidly Rotating Wormhole Space‐time

This study is purposed to elaborate the problem of energy 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 distributions of Einstein, Bergmann‐Thomson and Tolman definitions give the same results in Rigidly Rotating Wormhole space‐time.

Møller Energy–Momentum Complex in General Relativity for Higher Dimensional Universes

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 al., Rosen, and Johri et al. in four dimensions.