Yazar "Sharif, M" seçeneğine göre listele

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    Öğe
    Matter collineations in Kantowski-Sachs, Bianchi types I and III spacetimes
    (Springer/Plenum Publishers, 2003) Camci, U; Sharif, M
    The matter collineation classifications of Kantowski- Sachs, Bianchi types I and III space times are studied according to their degenerate and non-degenerate energy-momentum tensor. When the energy-momentum tensor is degenerate, it is shown that the matter collineations are similar to the Ricci collineations with different constraint equations. Solving the constraint equations we obtain some cosmological models in this case. Interestingly, we have also found the case where the energy-momentum tensor is degenerate but the group of matter collineations is finite dimensional. When the energy-momentum tensor is non-degenerate, the group of matter collineations is finite-dimensional and they admit either four which coincides with isometry group or ten matter collineations in which four ones are isometries and the remaining ones are proper.
  • [ X ]
    Öğe
    Matter collineations of spacetime homogeneous Godel-type metrics
    (Iop Publishing Ltd, 2003) Camci, U; Sharif, M
    The spacetime homogeneous Godel-type spacetimes which have four classes of metrics are studied according to their matter collineations. The results obtained are compared with Killing vectors and Ricci collineations. It is found that these spacetimes have an infinite number of matter collineations in the degenerate case, i.e. det(T-ab) = 0, and do not admit proper matter collineations in the non-degenerate case, i.e. det(T-ab) not equal 0. The degenerate case has the new constraints on the parameters m and w which characterize the causality features of the Godel-type spacetimes.