Related papers: Lookback time bounds from energy conditions
Current observational bounds on dark energy depend on assumptions about the curvature of the universe. We present a simple and efficient method for incorporating constraints from CMB anisotropy data, and use it to derive constraints on…
We investigate the cosmological evolution in a new modified teleparallel theory, called $f(T,B)$ gravity, which is formulated by connecting both $f(T)$ and $f(R)$ theories with a boundary term $B$. Here, $T$ is the torsion scalar in…
We deduce general expressions for the line element of universe models with positive spatial curvature described by conformally flat spacetime coordinates. Models with dust, radiation and vacuum energy are exhibited. Discussing the existence…
We present here the transformations required to recast the Robertson-Walker metric and Friedmann-Robertson-Walker equations in terms of observer-dependent coordinates for several commonly assumed cosmologies. The overriding motivation is…
We construct a FLRW universe considering an anisotropic scaling between space and time at extremely high and low energies only. In this context, Friedmann equations contain an additional term arising from spatial curvature which implements…
We discuss the cosmological reconstruction of $f(R,R_{\alpha\beta}R^{\alpha\beta},\phi)$ (where $R$, $R_{\alpha\beta}R^{\alpha\beta}$ and $\phi$ represents the Ricci scalar, Ricci invariant and scalar field) corresponding to power law and…
Some observational consequences of a cosmological scenario driven by adiabatic matter creation are investigated. Exact expressions for the lookback time, age of the universe, luminosity distance, angular diameter, and galaxy number counts…
Within the recently proposed structured FRW model universe the averaged Einstein equations are derived. The backreaction turns out to have an interesting behavior. Its equivalent density and pressure, being proportional, are negative at…
We present explicit expressions for the calculation of cosmological look back time, for zero cosmological constant and arbitrary density parameter $\Omega$, which, in the limit as redshift becomes infinite, give the age of the universe. The…
In this paper, we examined the viability bounds of a higher derivative $f(R,\Box R, T)$ theory through analyzing energy conditions (where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor, respectively). We take flat…
Here, we consider a flat FRW universe whose its horizon entropy meets the R\'enyi entropy of non-extensive systems. In our model, the ordinary energy-momentum conservation law is not always valid. By applying the Clausius relation as well…
In order to shed some light on the current discussion about f(R)-gravity theories we derive and discuss the bounds imposed by the energy conditions on a general f(R) functional form. The null and strong energy conditions in this framework…
The four principal energy conditions (ECs) in general relativity prohibit negative energies, repulsive gravity and superluminal energy flows. One must invoke exotic matter to violate any one of these, yet $\Lambda$CDM does so quite…
In this manuscript, we consider the extension of the Hilbert-Einstein action to analyze several interesting features of the theory. More specifically, the Lagrangian $f(R)$ is replaced by $f(R, L_m)$ in action, where $R$ is the Ricci…
In this study of the modified $f(Q)$ theory of gravity in the spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) spacetime, we explore all the affine connections compatible with the symmetric teleparallel structure; three classes…
Starting from the energy-momentum of matter and gravitational field in the framework of General Relativity and Teleparallel Gravity, we obtain the energy-momentum complex in flat FRW spacetime. We show that the complex vanishes at…
There are so many ideas that potentially explain the dark energy phenomenon, current research is focusing on a more in-depth analysis of the potential effects of modified gravity on both local and cosmic scales. In this paper we have…
An accelerated expansion phase is being experienced by the universe due to the presence of an unknown energy component known as dark energy (DE). To find out the cosmic evolution scientists ever tried to modify Einstein's gravitational…
The present paper examines the validity of energy bounds in a modified theory of gravity involving non-minimal coupling of torsion scalar and perfect fluid matter. In this respect, we formulate the general inequalities of energy conditions…
The near-zero value of the cosmological constant \Lambda in an equilibrium context may be due to the existence of a self-tuning relativistic vacuum variable q. Here, a cosmological nonequilibrium context is considered with a corresponding…