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AbstractWe prove that in space-times a velocity field that is shear, vorticity and acceleration-free, if any, is unique up to reflection, with these exceptions: generalized Robertson-Walker space-times whose space sub-manifold… Click to show full abstract
AbstractWe prove that in space-times a velocity field that is shear, vorticity and acceleration-free, if any, is unique up to reflection, with these exceptions: generalized Robertson-Walker space-times whose space sub-manifold is warped, and twisted space-times (the scale function is space-time dependent) whose space sub-manifold is doubly twisted. In space-time dimension $$n=4$$n=4, the Ricci and the Weyl tensors are specified, and the Einstein equations yield a mixture of two perfect fluids.
Journal Title: General Relativity and Gravitation
Year Published: 2019
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