No abstract

Matter collineations, as a symmetry property of the energy-momentum tensor Tab, are studied from the point of view of the Lie algebra of vector fields generating them. Most attention is given to space-times with a degenerate energy-momentum tensor. Some examples of matter collineations are found for dust fluids (including Szekeres's space-times), and null fluid space-times.

We describe a formalism and numerical approach for studying spherically symmetric scalar field collapse for arbitrary spacetime dimension d and cosmological constant Λ. The presciption uses a double null formalism, and is based on field redefinitions first used to simplify the field equations in generic 2−dimensional dilaton gravity. The formalism is used to construct code in which d and Λ are input parameters. We reproduce known results in d = 4 and d = 6 with Λ = 0, and present new results for d = 5 with zero and negative Λ. 04.70.Dy

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling of star interiors possessing elastic properties such as the ones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the way, a few general results for spacetimes admitting isometries are deduced, and their consequences are fully exploited in the case of spherical symmetry relating them next to the the case in which the material content of the spacetime is some elastic material. This paper extends and generalizes the pioneering work by Magli