We investigated the cosmology in a higher-curvature gravity where the dimensionality of spacetime gives rise to only quantitative difference, contrary to Einstein gravity. We found exponential type solutions for flat isotropic and homogeneous vacuum universe for the case in which the higher-curvature term in the Lagrangian density is quadratic in the scalar curvature, ξR 2. The solutions are cl...

A positive cosmological constant simplifies the asymptotics of forever expanding cosmological solutions of the Einstein equations. In this paper a general mathematical analysis on the level of formal power series is carried out for vacuum spacetimes of any dimension and perfect fluid spacetimes with linear equation of state in spacetime dimension four. For equations of state stiffer than radiat...

We investigated the cosmology in a higher-curvature gravity where the dimensionality of spacetime gives rise to only quantitative difference, contrary to Einstein gravity. We found exponential type solutions for flat isotropic and homogeneous vacuum universe for the case in which the higher-curvature term in the Lagrangian density is quadratic in the scalar curvature, ξR 2. The solutions are cl...

The nature of gravitational collapse was the subject of debate and controversy for much of the last century. During the 1960’s and 1970’s our understanding of general relativity consolidated and culminated in our modern understanding of black holes and spacetime singularities. Since then, there has been significant advances in understanding the dynamics of gravitational collapse and the nature ...

This research work examines the standard static spacetime (SSST) in terms of almost Ricci-Yamabe soliton with conformal vector field. It is shown that function ? satisfies Poisson-Laplace equation. Next, we consider harmonic and discuss aspect on SSST. In addition, investigate nature SSST non-rotating Killing Also, exhibit non-steady non shrinking i.e., ?? 0 smooth, connected, non-compact field...

We thoroughly investigate conformally Schwarzschild spacetimes in different coordinate systems to seek for physically reasonable models of a cosmological black hole. assume that conformal factor depends only on the time and spacetime is asymptotically flat Friedmann-Lema\^{\i}tre-Robertson-Walker universe filled by perfect fluid obeying linear equation state $p=w\rho$ with $w>-1/3$. In this cla...

A class of perfect fluid collapse models is constructed to examine the final fate of a continual gravitational collapse. While the pressure could be negative in the interior of the cloud, the weak-energy condition is satisfied. The collapsing star radiates away its matter as the process of gravitational collapse evolves, so as to avoid the formation of trapped surfaces. The collapsing interior ...

In this article, a special static spherically symmetric perfect fluid solution of Einstein’s equations is provided. Though pressure and density both diverge at the origin, their ratio remains constant. The solution presented here fails to give positive pressure but nevertheless, it satisfies all energy conditions. In this new spacetime geometry, the metric becomes singular at some finite value ...

Gauge-invariant treatments of the second-order cosmological perturbation in a four dimensional homogeneous isotropic universe are formulated without any gauge fixing. We have derived the Einstein equations in the case of the single perfect fluid without ignoring any modes. These equations imply that any types of mode-coupling arise due to the second-order effects of the Einstein equations. The ...

We study two types of axially symmetric, stationary and asymptotically flat spacetimes using highly accurate numerical methods. One type contains a black hole surrounded by a perfect fluid ring and the other a rigidly rotating disc of dust surrounded by such a ring. Both types of spacetime are regular everywhere (outside of the horizon in the case of the black hole) and fulfil the requirements ...