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    Öğe
    Conformal Ricci collineations of static spherically symmetric spacetimes
    (Int Academic Publishers Ltd, 2008) Camci, Ugur; Qadir, Asghar; Saifullah, K.
    Conformal Ricci collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating conformal Ricci collineations is found when the Ricci tensor is non-degenerate, in which case the number of independent conformal Ricci collineations is 15, the maximum number for four-dimensional manifolds. In the degenerate case it is found that the static spherically symmetric spacetimes always have an infinite number of conformal Ricci collineations. Some examples are provided which admit non-trivial conformal Ricci collineations, and perfect fluid source of the matter.
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    Öğe
    Noether symmetries of Bianchi I, Bianchi III, and Kantowski-Sachs spacetimes in scalar-coupled gravity theories
    (Amer Physical Soc, 2007) Camci, Ugur; Kucukakca, Yusuf
    We consider some scalar-coupled theories of gravity, including induced gravity, and study the Noether symmetries of Bianchi I, Bianchi III, and Kantowski-Sachs cosmological models for this theory. For various forms of coupling of the scalar field with gravity, some potentials are found in these cosmological models under the assumption that the Lagrangian admits Noether symmetry. The solutions of the field equations for the considered models are presented by using the results obtained from the Noether symmetry. We also find the explicit form of the scalar field in terms of the conformal time for Bianchi I, III, and Kantowski-Sachs models.
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    Öğe
    Ricci collineations in Bianchi II spacetime
    (World Scientific Publishing Co. Pte Ltd, 2007) Camci, Ugur
    In this study we classify the Ricci collineations (RCs) of Bianchi II spacetime according to the degenerate and non-degenerate cases of the Ricci tensor. It is shown that we have thirteen possibilities to be considered for the degenerate case, and found that there are generally infinitely many RCs whereas some cases give finite dimensional Lie algebras of the RCs which have three, four or five RCs. For the non-degenerate Ricci tensor cases, the Lie algebra of the obtained RCs are finite dimensional, in which the number of RCs is also three, four or five. Copyright © 2007 by World Scientific Publishing Co. Pvt. Ltd.