We 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, the Ricci and the Weyl tensors are specified, and the Einstein equations yield a mixture of two perfect fluids.
On the uniqueness of a shear-vorticity-acceleration-free velocity field in space-times / L.G. Molinari, A. Tacchini, C.A. Mantica. - In: GENERAL RELATIVITY AND GRAVITATION. - ISSN 0001-7701. - 51:9(2019 Sep).
On the uniqueness of a shear-vorticity-acceleration-free velocity field in space-times
L.G. MolinariPrimo
;C.A. Mantica
Ultimo
2019
Abstract
We 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, the Ricci and the Weyl tensors are specified, and the Einstein equations yield a mixture of two perfect fluids.
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