Abstract. We study half lightlike submanifolds of an indefinite Sasakian manifold. The aim of this paper is to prove the following result: If a locally symmetric half lightlike submanifold of an indefinite Sasakian manifold is totally umbilical, then it is of constant positive curvature 1. In addition to this result, we prove three characterization theorems for such a half lightlike submanifold.
IntroductionThe class of lightlike submanifolds of codimension 2 is composed entirely of two classes by virtue of the rank of its radical distribution, named by half lightlike or coisotropic submanifolds [3]. Half lightlike submanifold is a special case of r-lightlike submanifold [2] such that r = 1 and its geometry is more general form than that of coisotrophic submanifolds. Much of the works on half lightlike submanifolds will be immediately generalized in a formal way to arbitrary r-lightlike submanifolds. Recently several authors have studied the geometry of lightlike submanifolds of an indefinite Sasakian manifold. Many works of such lightlike submanifolds assumed that M is totally umbilical (or totally geodesic), or M is screen conformal, or its screen distribution S(T M ) is totally umbilical in M .In the theory of Sasakian manifolds, the following result is well-known: If a Sasakian manifold is locally symmetric, then it is of constant positive curvature 1. We proved lightlike hypersurface version of the above classical result: If a locally symmetric lightlike hypersurface of an indefinite Sasakian manifold is totally geodesic, then it is of constant positive curvature 1 [5].