∗Research supported in part by NSF grant INT-9903302.
In previous work a hyperbolic twistor space over a paraquaternionic
Kähler manifold was defined, the fibre being the hyperboloid model
of the hyperbolic plane with constant curvature −1. Two almost complex
structures were defined on this twistor space and their properties studied.
In the present paper we consider a twistor space over a paraquaternionic Kähler
manifold with fibre given by the hyperboloid of 1-sheet, the anti-de-Sitter
plane...
This paper studies conformal and related changes of the product metric on the product of two almost contact metric manifolds. It is shown that if one factor is Sasakian, the other is not, but that locally the second factor is of the type studied by Kenmotsu. The results are more general and given in terms of trans-Sasakian, α-Sasakian and β-Kenmotsu structures.
Let be an -dimensional Riemannian manifold admitting a covariant constant endomorphism of the localized module of 1-forms with distinct non-zero eigenvalues. After it is shown that is locally flat, a manifold immersed in is studied. The manifold has an induced structure with of the same eigenvalues if and only if the normal to is a fixed direction of . Finally conditions under which is invariant under , is totally geodesic and the induced structure has vanishing Nijenhuis...
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