Sharp pinching theorems for complete submanifolds in the sphere

Abstract For every complete and minimally immersed submanifold f: M n → S n + p f M^n^n+p whose second fundamental form satisfies | A | 2 ≤ n ⁢ p / (2 ⁢ p − 1) A^2 np/ (2p-1), we prove that it is either totally geodesic, or (a covering of) a Clifford torus or a Veronese surface in S 4 S^4, thereby extending the well-known results by Simons, Lawson and Chern, do Carmo & Kobayashi from compact to complete M n M^n. We also obtain the corresponding result for complete hypersurfaces with non-vanishing constant mean curvature, due to Alencar & do Carmo in the compact case, under the optimal bound on the umbilicity tensor. In dimension n ≤ 6 n 6, a pinching theorem for complete higher-codimensional submanifolds with non-vanishing parallel mean curvature is proved, partly generalizing previous work by Santos. Our approach is inspired by the conformal method of Fischer-Colbrie, Shen & Ye and Catino, Mastrolia & Roncoroni.