Related papers: Energy Conditions in a Generalized Second-Order Sc…
We study the late time evolution of flat and negatively curved Friedmann-Robertson-Walker (FRW) models with a perfect fluid matter source and a scalar field arising in the conformal frame of $f(R)$ theories nonminimally coupled to matter.…
Recently, a de-Sitter epoch has been found in the new model of loop quantum cosmology which is governed by the scalar constraint with both of Euclidean and Lorentz terms. The singularity free bounce in the new LQC model and the emergent…
Energy conditions are attempts to summarise the properties of realistic descriptions of matter via constraints on the energy-momentum tensor. This is, for example, useful when one wants to understand the types of spacetime geometry that can…
The methods of dynamical systems have found wide applications in cosmology, with focus either upon inflation or upon the passage into dark energy era. In this paper, we endeavor to capture the whole history of the universe into a dynamical…
We discuss the motivation for high accuracy relativistic gravitational experiments in the Solar System and complementary cosmological tests. We focus our attention on the issue of distinguishing a generic scalar-theory of gravity as the…
In isotropic loop quantum cosmology, non-perturbatively modified dynamics of a minimally coupled scalar field violates weak, strong and dominant energy conditions when they are stated in terms of equation of state parameter. The violation…
Among the possible extensions of General Relativity that have been put forward in order to address some long standing issues in our understanding of the Universe, Scalar-Tensor Theories have received a lot of attention for their simplicity.…
We investigate a flat FLRW-model in $f(R,T)$-gravity, which includes the quadratic variation in scalar curvature $R$ and the linear term of the trace of the stress-energy tensor $T$. In turn, we establish the model has the behaviour of the…
Apart from the familiar structure firmly-rooted in the general relativistic field equations where the energy--momentum tensor has a null divergence i.e., it conserves, there exists a considerable number of extended theories of gravity…
We have investigated an isotropic and homogeneous cosmological model of the universe in $f(R, T^{\phi})$ gravity, where $T^{\phi}$ is the trace of the energy-momentum tensor and $R$ is the Ricci scalar. We developed and presented exact…
This note summarizes a model-independent analysis of the age of the universe problem that trades off precision in favour of robustness: The energy conditions of Einstein gravity are designed to extract as much information as possible from…
We apply a simple decomposition to the energy of a moving particle. Based on this decomposition, we identify the potential and kinetic energies, then use them to give general definitions of momentum and the various kinds of forces exerted…
In this work, we have considered the flat FRW model of the universe filled with electro-magnetic field. First, the Maxwell's electro-magnetic field in linear form has been discussed and after that the modified Lagrangian in non-linear form…
We study a new type of the modified teleparallel gravity of the form $F(T,\,\Theta)$ in which $T$, the torsion scalar, is coupled with $\Theta$, the trace of the stress-energy tensor. In a perturbational approach, we study the stability of…
We consider scalar tensor theories of gravity assuming that the scalar field is non minimally coupled with gravity. We use this theory to study evolution of a flat homogeneous and isotropic universe. In this case the dynamical equations can…
A lagrangian for the $k-$ essence field is set up with canonical kinetic terms and incorporating the scaling relation of [1]. There are two degrees of freedom, {\it viz.},$q(t)= ln\enskip a(t)$ ($a(t)$ is the scale factor) and the scalar…
The aim of this paper is to explore warm inflation in the background of $f(\mathcal{G})$ theory of gravity using scalar fields for the FRW universe model. We construct the field equations under slow-roll approximations and evaluate the…
We define and compute the energy of higher curvature gravity theories in arbitrary dimensions. Generically, these theories admit constant curvature vacua (even in the absence of an explicit cosmological constant), and asymptotically…
Important observables to reveal the nature of dark energy are the equation of state $w$ and its time derivative in units of the Hubble time $w'$. Recently, it is shown that the simplest scalar field models of dark energy (quintessence)…
A review on spatially flat D-dimensional Friedmann-Robertson-Walker (FRW) model of the universe has been performed. Some standard parameterizations of the equation of state parameter of the Dark Energy models are proposed and the…