On certain principal directions in lightlike hypersurfaces of an indefinite Sasakian manifold

Abstract

We study lightlike hypersurfaces of an indefinite almost contact metric-manifold M . We prove that there are only two types of such hypersurfaces, known as ascreen and inascreen, with respect to the position of the structure vector field of M . We also show that the second class of hypersurfaces naturally admits an almost Hermitian structure.