We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f (R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f (R) models, small perturbations of shear are damped, ...

This paper is devoted to investigate cylindrical solutions in mimetic gravity. The explicit forms of the metric of this theory, namely mimetic-Kasner (say) have been obtained. In this study we have noticed that the Kasner’s family of exact solutions needs to be reconsidered under this type of modified gravity. A no-go theorem is proposed for the exact solutions in the presence ...

This paper is devoted to an analysis of the dynamical instability of a self-gravitating object that undergoes a collapse process. We take the framework of generalized teleparallel gravity with a cylindrically symmetric gravitating object. The matter distribution is represented by a locally anisotropic energy-momentum tensor. We develop basic equations such as the dynamical ...

In this paper,we investigate the mathematical modeling for the cosmological attractors propagated in mimetic gravity upon which an interacting dark energy-dark matter is supposed to be existed. The average value of the interaction of these percentages, namely i say, may be used to investigate generally the modeling of an attractor; the actual value could only be determined ...

In this paper, we investigate a simple class of Horndeski models where the scalar field plays the role of a k-essence fluid. We present several solutions for earlytime universe, namely inflation and cosmological bounce, by making use of some reconstruction technique. Moreover, we furnish the formalism to calculate perturbations in FRW space-time and we compute the spectral ...

In this paper, we investigated inflationary solutions for a subclass of Horndeski models where a scalar field is non-minimally coupled with the Gauss–Bonnet invariant. Examples of canonical scalar field and k-essence to support the early-time acceleration are considered. The formalism to calculate the perturbations in a Friedmann–Robertson–Walker (FRW) universe and to derive ...

In this paper, we analyze a simple class of Horndeski scalar-tensor theory. We investigate several cosmological solutions for inflation, bounce scenario and finite future-time singularities. Perturbations respect to Friedmann-Robertson-Walker metric are studied and discussed in the context of inflation.