Warped Product Semi-Invariant Submanifolds in Almost Paracontact Riemannian Manifolds

We show that there exist no proper warped product semi-invariant submanifolds in almost paracontact Riemannian manifolds such that totally geodesic submanifold and totally umbilical submanifold of the warped product are invariant and anti-invariant, respectively. Therefore, we consider warped product semi-invariant submanifolds in the form N = N-perpendicular to x N-f(T) by reversing two factor manifolds N-T and N-perpendicular to. We prove several fundamental properties of warped product semi-invariant submanifolds in an almost paracontact Riemannian manifold and establish a general inequality for an arbitrary warped product semi-invariant submanifold. After then, we investigate warped product semi-invariant submanifolds in a general almost paracontact Riemannian manifold which satisfy the equality case of the inequality. Copyright (C) 2009 Mehmet Atceken.