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, ...

It is shown that the inflationary model is the result of the symmetry of the generalized F(R, T, X, ϕ)-cosmological model using the Noether symmetry. It leads to a solution, a particular case of which is Starobinsky’s cosmological model. It is shown that even in the more particular case of cosmological models F(R, X, ϕ) and F(T, X, ϕ) the Monge–Ampère equation is still obtained, ...

We investigated the gravity model F (R, T), which interacts with a fermion field in a uniform and isotropic flat spacetime FLRW. The main idea and purpose of the work done was to create a mathematical model and find a particular solution for the scale factor a, since it describes the dynamics of the evolution of the Universe. The solutions for this universe are obtained using ...

In this work, we shall exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. S. Weinberg has also produced significant works related to the primordial gravitational waves, with the most important one being the effects of neutrinos on primordial gravitational waves. With this short review, our main aim is to ...

Slow-roll inflation is analyzed in the context of modified gravity within the Palatini formalism. As shown in the literature, inflation in this framework requires the presence of non-traceless matter; otherwise, it does not occur just as a consequence of the nonlinear gravitational terms of the action. Nevertheless, by including a single scalar field that plays the role of the ...

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 ...

Yerzhanov, K.; Bauyrzhan, G.; Altaibayeva, A.; Myrzakulov, R. Inflation from the Symmetry of the Generalized Cosmological Model. Symmetry 2021, 13, 2254. https:// doi.org/10.3390/sym13122254