Surfaces with parallel normalized mean curvature vector

A surfaceM in a Riemannian manifold is said to have parallel normalized mean curvature vector if the mean curvature vector is nonzero and the unit vector in the direction of the mean curvature vector is parallel in the normal bundle. In this paper, it is proved that every analytic surface in a euclideanm-spaceE^m with parallel normalized mean curvature vector must either lies in aE⁴ or lies in a hypersphere ofE^m as a minimal surface. Moreover, it is proved that if a Riemann sphere inE^m has parallel normalized mean curvature vector, then it lies either in aE³ or in a hypersphere ofE^m as a minimal surfaces. Applications to the classification of surfaces with constant Gauss curvature and with parallel normalized mean curvature vector are also given.