Lagrangian spheres in the 2-dimensional complex space forms

By constructing a holomorphic cubic form for Lagrangian surfaces with nonzero constant length mean curvature vector in a 2-dimensional complex space form (M) over tilde (4c), we characterize the Lagrangian pesudosphere as the only branched Lagrangian immersion of a sphere in (M) over tilde (4c) with nonzero constant length mean curvature vector. When c = 0, our result reduces to Castro-Urbano's result in [1].