No abstract

In the present paper, firstly, the definition of pseudo conharmonically symmetric Riemannian manifold is given. In the second section, some theorems about these manifolds are proved. In the third section, pseudo conharmonically symmetric spacetime is investigated. Under some special conditions, we examine the properties of this spacetime.

The aim of the present paper is to obtain the condition under which a pseudosymmetric spacetime to be a perfect fluid spacetime. It is proven that a pseudosymmetric generalized Robertson-Walker spacetime is a perfect fluid spacetime. Moreover, we establish that a conformally flat pseudosymmetric spacetime is a generalized Robertson-Walker spacetime. Next, it is shown that a pseudosymmetric dust fluid with constant scalar curvature satisfying Einstein's field equations without cosmological constant is vacuum. Finally, we construct a non-trivial example of pseudosymmetric spacetime.

The object of the present paper is to study the Z-symmetric manifold with the projective curvature tensor. At first, we study the case of Z-tensor and projective Ricci tensor being of Codazzi type. Next, we consider recurrent Z-tensor and recurrent projective Ricci tensor. We also study the Z-symmetric manifold with projective curvature tensor with divergence-free Z-tensor. Finally, we construct an example of the Z-symmetric manifold with projective curvature tensor.