Quadratically varying deceleration parameter in f(R,T) gravity

In this paper, we have proposed a new form for the varying deceleration parameter that is a generalization of the form of Ö. Akarsu and T. Dereli [Cosmological models with linearly varying deceleration parameter, Int. J. Theor. Phys. 51(2012) 612]. LRS Bianchi type-I cosmological model filled with a perfect fluid source in [Formula: see text] gravity theory, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the stress energy–momentum tensor, has been studied in order to investigate early time deceleration and late time acceleration of the universe by using this new form of time-varying deceleration parameter. The time evolution of physical and dynamical parameters have been analyzed and shown by graphs. Moreover, the deceleration parameter has been considered in terms of redshift. It has been shown that the model starts with a big bang and ends with a big rip. It is filled by a quintessence like fluid at the early time and by a phantom like fluid at the late time.

Anisotropic universe models with magnetized strange quark matter in f(R) gravity theory

In this study, we have investigated generalized anisotropic universe models for magnetized strange quark matter (MSQM) distribution in the framework of [Formula: see text] 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.

Various dark energy models for variables G and Λ in f(R, T) modified theory

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 [Formula: see text] 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 [Formula: see text] and Hubble parameter. Also, we have discussed some physical behavior of the models with various graphics.

Cosmological Models in Lyra Geometry with Linearly Varying Deceleration Parameter

Cosmological models with linearly varying deceleration parameter in the cosmological theory based on Lyra’s geometry have been discussed. Exact solutions have been obtained for a spatially flat FRW model by considering a time dependent displacement field. We have also obtained the time periods during which the universe undergoes decelerated and accelerated expansions for a matter-dominated universe.

Cosmology in modified f(R,T)-gravity theory in a variant Λ(T) scenario-revisited

Three new cosmological models of the present Universe are obtained with [Formula: see text] modified theory of gravity proposed by Harko et al. [Phys. Rev. D 84 (2011) 024020, arXiv:1104.2669 [gr-qc]] in a general class of Bianchi space-time. In this paper, we have generalized the modified [Formula: see text] field equations with [Formula: see text]-gravity, where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the stress–energy–momentum tensor, respectively. To find the deterministic solutions we have considered the linearly varying deceleration parameter [Formula: see text] proposed by Akarsu and Dereli [Cosmological models with linearly varying deceleration parameter, Int. J. Theor. Phys. 51 (2011) 612]. We have made the analyses of the variation of pressure, energy density and cosmological term with cosmic time. It is observed that our derived models are unstable in early time whereas they are stable at late and future time (i.e. at present epoch). The physical and geometric properties of all three models are studied in detail.

Anisotropic magnetized holographic Ricci dark energy cosmological models

In this paper, we have considered spatially homogeneous and anisotropic Bianchi type-III space–time filled with matter and anisotropic modified holographic Ricci dark energy in general relativity. We have solved Einstein’s field equations using the following possibilities: (i) hybrid expansion law proposed by Akarsu et al. (JCAP, 01, 022 (2014)); (ii) a varying deceleration parameter considered by Mishra et al. (Int. J. Theor. Phys. 52, 2546 (2013)); and (iii) a linearly varying deceleration parameter given by Akarsu and Dereli (Int. J. Theor. Phys. 51, 612 (2012)). We have presented the cosmological models in each of the preceding cases and studied their evolutions. We have also discussed physical and kinematical properties of the models.

Bianchi type-V modified holographic Ricci dark energy models in Saez–Ballester theory of gravitation

We have investigated Bianchi type-V universe filled with matter and modified holographic Ricci dark energy in a scalar–tensor theory proposed by Saez–Ballester (Phys. Lett. A, 113, 467 (1986)). To get a determinate solution, we have used (i) hybrid expansion law (Akarsu et al. JCAP, 01, 022 (2014)), (ii) varying deceleration parameter (Mishra et al. Int. J. Theor. Phys. 52, 2546 (2013)), and (iii) linearly varying deceleration parameter (Akarsu and Dereli. Int. J. Theor. Phys. 51, 612 (2012)). The various physical and geometrical aspects of the models are also discussed.