An Invariant of Riemannian Type for Legendrian Warped Product Submanifolds of Sasakian Space Forms

In the present paper, we investigate the geometry and topology of warped product Legendrian submanifolds in Sasakian space forms D2n+1(epsilon) and obtain the first Chen inequality that involves extrinsic invariants like the mean curvature and the length of the warping functions. This inequality also involves intrinsic invariants (delta-invariant and sectional curvature). In addition, an integral bound is provided for the Bochner operator formula of compact warped product submanifolds in terms of the gradient Ricci curvature. Some new results on mean curvature vanishing are presented as a partial solution to the well-known problem given by S.S. Chern.