We study the five-dimensional spherical collapse of an inhomogeneous dust in the presence of a positive cosmological constant. The general interior solutions, in the closed form, of the Einstein field equations, i.e. the 5D Tolman-Bondi-de Sitter, is obtained which in turn is matched to the exterior 5D Schwarzschild-de Sitter. It turns out that the collapse proceeds in the same way as in the Minkowski background, i.e. the strong curvature naked singularities form and thus violate the cosmic censorship conjecture. A brief discussion on the causal structure singularities and horizons is also given.
We consider a magnetic cylindrically symmetric universe with a plane-symmetric inhomogeneous viscous fluid cosmological model with electromagnetic field. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. To get a determinate solution, we assume the free gravitational field to be Petrov type-II non-degenerate. Without assuming any ad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor together with some physical aspects of the model are also discussed.
We consider a magnetic cylindrically symmetric universe with two degrees of freedom in the presence of an electrically neutral viscous fluid. The source of the magnetic field is an electric current along the x-axis. The coefficient of bulk viscosity is assumed to be a power function of the mass density. Without assuming any adhoc law, we obtain a cosmological constant as a decreasing function of time which is supported by results from recent supernovae observations. *
We discuss the spherical collapse of a two fluid system: a string fluid and a null fluid described by a generalized Vaidya metric. This led us to explicitly describe the effect of a string fluid on the established picture of a null fluid collapse (Vaidya collapse). It is found that there is a shrinkage of the initial data space for naked singularities of Vaidya collapse upon taking into account a string fluid. The implications of the results in the context of the cosmic censorship conjecture are discussed.
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