Abstract:
The following question is considered: Which quasi-Sasakian (cosymplectic, Sasakian, or proper quasi-Sasakian) structures admit nontrivial concircular transformations of their metrics (i.e., determine Fialkow spaces), and under what conditions. It is proved that any cosymplectic manifold is a Fialkow space. Necessary and sufficient conditions for a Sasakian or a quasi-Sasakian manifold to be a Fialkow space are obtained. A fairly large class of Sasakian manifolds which are not Fialkow spaces is described.
Keywords:quasi-Sasakian structure, concircular transformation of a metric, Fialkow space, cosymplectic manifold, Sasakian manifold, Kenmotsu manifold.