Abstract. In this paper, we classify 3-dimensional Lagrangian Willmore submanifolds of the nearly kaehler 6-sphere S 6 (1) with constant scalar curvature.2000 Mathematics Subject Classification. 53 B 25; 53 D 12; 53 C 42.
Introduction.It is well known that a 6-dimensional sphere S 6 (1) admits an almost kaehler structure J by making use of the Cayley system. Many interesting theorems about the topology and the geometry of nearly kaehler manifolds have been proved (see [2,4,7]). There have been many results on geometry of submanifolds in a kaehler manifold. Especially, submanifolds (called Lagrangian submanifolds) for which J interchanges the tangent and normal spaces. The theory of Lagrangian submanifolds in a nearly kaehler manifold was studied by many authors (cf. e.g. N. Ejiri, B. Y. Chen, F. Dillen, L. Vrancken and L. Verstraelen etc.). About Lagrangian submanifolds of S 6 (1), in [5], the authors classified the compact Lagrangian submanifolds of S 6 (1) whose sectional curvatures satisfy K ≥ 1 16 . In [2], the authors classified the Lagrangian submanifolds of S 6 (1) with constant scalar curvature that realize the Chen's inequality. In this paper, we classify Lagrangian Willmore submanifold of the nearly kaehler 6-sphere S 6 (1) with constant scalar curvature and obtain all possible values for the norm square of the second fundamental form S about these submanifolds. It is similar to Chern's conjecture which states that the set of all possible values for S of a compact minimal submanifold in the sphere with S = constant is a limit set.