A new class of exact solutions of Einstein’s field equations with a perfect fluid source, variable gravitational coupling G and cosmological term Λ for FRW spacetime is obtained by considering variable deceleration parameter models for the universe. The nature of the variables G(t), Λ(t) and the energy density ρ(t) have been examined for three cases : (i) exponential (ii) polynomial and (iii) s...

The Einstein equations for a perfect fluid spatially homogeneous spacetime are studied in a unified manner by retaining the generality of certain parameters whose discrete values correspond to the various Bianchi types of spatial homogeneity. A parameter dependent decomposition of the metric variables adapted to the symmetry breaking effects of the nonabelian Bianchi types on the “free dynamics...

We study the closed universe recollapse conjecture for positively curved FRW models with a perfect fluid matter source and a scalar field which arises in the conformal frame of the R+ αR theory. By including ordinary matter, we extend the analysis of a previous work. We analyze the structure of the resulted fourdimensional dynamical system with the methods of the center manifold theory and the ...

We consider the propagation of nonlinear sound waves in a perfect fluid at rest. By employing Riemann wave equation acoustics one spatial dimension, it is shown that carrying constant density perturbation their tails produce an acoustic analogue gravitational memory. For memory, which general nonlinear, nonlinearity effective spacetime dynamics not due to Einstein equations, but equations. conc...

We study the late-time behaviour of tilted perfect fluid Bianchi type III models using a dynamical systems approach. We consider models with dust, and perfect fluids stiffer than dust, and eludicate the late-time behaviour by studying the centre manifold which dominates the behaviour of the model at late times. In the dust case, this centre manifold is 3-dimensional and can be considered as a d...

We discuss the question of how the number of dimensions of space and time can influence the equilibrium configurations of stars. We find that dimensionality does increase the effect of mass but not the contribution of the pressure, which is the same in any dimension. In the presence of a (positive) cosmological constant the condition of hydrostatic equilibrium imposes a lower limit on mass and ...

We analyze the boson mixing in curved spacetime and compute expectation value of energy-momentum tensor bosons on flavor vacuum spatially flat Friedmann-Lemaitre-Robertson-Walker metrics. show that behaves as effective a perfect fluid. Assuming fixed de Sitter background, we equation state can assume values interval [-1, 1], and, limit has -1, which is one dark energy. The results here presente...

Quantum mechanics, superfluids, and capillary fluids are closely related: it is thermodynamics that links them. In this paper, the Liu procedure used to analyze thermodynamic requirements. A comparison with traditional method of divergence separation highlights role spacetime. It shown perfect Korteweg holographic. The conditions under which a complex field can represent density velocity fields...

We carry out numerical simulations of the gravitational collapse a perfect fluid with ultrarelativistic equation state $P=\kappa\rho$, in spherical symmetry $2+1$ spacetime dimensions $\Lambda<0$. At threshold prompt collapse, we find type II critical phenomena (apparent horizon mass and maximum curvature scale as powers distance from threshold) for $\kappa\gtrsim 0.43$, I (lifetime scales loga...

We propose a new, augmented formulation of the coupled Euler-Einstein equations for perfect fluids on plane-symmetric Gowdy spacetimes. The unknowns of the augmented system are the density and velocity of the fluid and the firstand second-order spacetime derivatives of the metric. We solve the Riemann problem for the augmented system, allowing propagating discontinuities in both the fluid varia...