Cosmology-in-three-dimensions：steps-towards-the-general-solution.pdfVIP

Cosmology in three dimensions: steps towards the general solution 1 1 2 John D. Barrow , Douglas J. Shaw and Christos G. Tsagas 1DAMTP, Centre for Mathematical Sciences, University of Cambridge Wilberforce Road, Cambridge CB3 0WA, UK 2Section of Astrophysics, Astronomy and Mechanics, Department of Physics Aristotle University of Thessaloniki, Thessaloniki 54124, Greece June 10, 2006 Abstract We use covariant and first-order formalism techniques to study the properties of general relativistic cosmology in three dimensions. The covariant approach provides an irreducible decomposition of the relativistic equations, which allows for a mathematically compact and physically transparent description of the 3-dimensional spacetimes. Using this information we review the features of homogeneous and isotropic 3-d cosmologies, provide a number of new solutions and study gauge invariant perturbations around them. The first-order formalism is then used to provide a detailed study of the most general 3-d spacetimes containing perfect- fluid matter. Assuming the material content to be dust with comoving spatial 2-velocities, we find the general solution of the Einstein equations with non-zero (and zero) cosmological constant and generalise known solutions of Kriele and the 3-d counterparts of the Szekeres solutions. In the case of a non-comoving dust fluid we find the general solution in the case of one non-zero fluid velocity component. We consider the asymptotic behaviour of the families of 3-d cosmologies wi