Given an immersed submanifold x : M^M → S^n in the unit sphere S^n without umbilics, a Blaschke eigenvalue of x is by definition an eigenvalue of the Blaschke tensor of x. x is called Blaschke isoparametric if its M...Given an immersed submanifold x : M^M → S^n in the unit sphere S^n without umbilics, a Blaschke eigenvalue of x is by definition an eigenvalue of the Blaschke tensor of x. x is called Blaschke isoparametric if its Mobius form vanishes identically and all of its Blaschke eigenvalues are constant. Then the classification of Blaschke isoparametric hypersurfaces is natural and interesting in the MSbius geometry of submanifolds. When n = 4, the corresponding classification theorem was given by the authors. In this paper, we are able to complete the corresponding classification for n = 5. In particular, we shall prove that all the Blaschke isoparametric hypersurfaces in S^5 with more than two distinct Blaschke eigenvalues are necessarily Mobius isoparametric.展开更多
For an immersed submanifold x : M^m→ Sn in the unit sphere S^n without umbilics, an eigenvalue of the Blaschke tensor of x is called a Blaschke eigenvalue of x. It is interesting to determine all hypersurfaces in Sn...For an immersed submanifold x : M^m→ Sn in the unit sphere S^n without umbilics, an eigenvalue of the Blaschke tensor of x is called a Blaschke eigenvalue of x. It is interesting to determine all hypersurfaces in Sn with constant Blaschke eigenvalues. In this paper, we are able to classify all immersed hypersurfaces in S^m+1 with vanishing MSbius form and constant Blaschke eigenvalues, in case (1) x has exact two distinct Blaschke eigenvalues, or (2) m = 3. With these classifications, some interesting examples are also presented.展开更多
In this paper, we obtain a formula for submanifolds in Sn+p by calculating the Laplacian of the Moebius second fundamental form. Using this formula, we obtain some pinching theorems about the minimal eigenvalue of the...In this paper, we obtain a formula for submanifolds in Sn+p by calculating the Laplacian of the Moebius second fundamental form. Using this formula, we obtain some pinching theorems about the minimal eigenvalue of the Blaschke tensor.展开更多
Abstract Let M^2 be an umbilic-free surface in the unit sphere S^3. Four basic invariants of M^2 under the Moebius transformation group of S^3 are Moebius metric g, Blaschke tensor A, Moebius second fundamental form B...Abstract Let M^2 be an umbilic-free surface in the unit sphere S^3. Four basic invariants of M^2 under the Moebius transformation group of S^3 are Moebius metric g, Blaschke tensor A, Moebius second fundamental form B and Moebius form φ. We call the Blaschke tensor is isotropic if there exists a smooth function λ such that A = λg. In this paper, We classify all surfaces with isotropic Blaschke tensor in S^3.展开更多
Let x : M→S^n+1 be a hypersurface in the (n + 1)-dimensional unit sphere S^n+1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n+1 are Mobius metric, Mobius form, M...Let x : M→S^n+1 be a hypersurface in the (n + 1)-dimensional unit sphere S^n+1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n+1 are Mobius metric, Mobius form, Mobius second fundamental form and Blaschke tensor. In this paper, we prove the following theorem: Let x : M→S^n+1 (n≥2) be an umbilic free hypersurface in S^n+1 with nonnegative Mobius sectional curvature and with vanishing Mobius form. Then x is locally Mobius equivalent to one of the following hypersurfaces: (i) the torus S^k(a) × S^n-k(√1- a^2) with 1 ≤ k ≤ n - 1; (ii) the pre-image of the stereographic projection of the standard cylinder S^k × R^n-k belong to R^n+1 with 1 ≤ k ≤ n- 1; (iii) the pre-image of the stereographic projection of the Cone in R^n+1 : -↑x(u, v, t) = (tu, tv), where (u,v, t)∈S^k(a) × S^n-k-1( √1-a^2)× R^+.展开更多
文摘Given an immersed submanifold x : M^M → S^n in the unit sphere S^n without umbilics, a Blaschke eigenvalue of x is by definition an eigenvalue of the Blaschke tensor of x. x is called Blaschke isoparametric if its Mobius form vanishes identically and all of its Blaschke eigenvalues are constant. Then the classification of Blaschke isoparametric hypersurfaces is natural and interesting in the MSbius geometry of submanifolds. When n = 4, the corresponding classification theorem was given by the authors. In this paper, we are able to complete the corresponding classification for n = 5. In particular, we shall prove that all the Blaschke isoparametric hypersurfaces in S^5 with more than two distinct Blaschke eigenvalues are necessarily Mobius isoparametric.
文摘For an immersed submanifold x : M^m→ Sn in the unit sphere S^n without umbilics, an eigenvalue of the Blaschke tensor of x is called a Blaschke eigenvalue of x. It is interesting to determine all hypersurfaces in Sn with constant Blaschke eigenvalues. In this paper, we are able to classify all immersed hypersurfaces in S^m+1 with vanishing MSbius form and constant Blaschke eigenvalues, in case (1) x has exact two distinct Blaschke eigenvalues, or (2) m = 3. With these classifications, some interesting examples are also presented.
文摘In this paper, we obtain a formula for submanifolds in Sn+p by calculating the Laplacian of the Moebius second fundamental form. Using this formula, we obtain some pinching theorems about the minimal eigenvalue of the Blaschke tensor.
文摘Abstract Let M^2 be an umbilic-free surface in the unit sphere S^3. Four basic invariants of M^2 under the Moebius transformation group of S^3 are Moebius metric g, Blaschke tensor A, Moebius second fundamental form B and Moebius form φ. We call the Blaschke tensor is isotropic if there exists a smooth function λ such that A = λg. In this paper, We classify all surfaces with isotropic Blaschke tensor in S^3.
文摘Let x : M→S^n+1 be a hypersurface in the (n + 1)-dimensional unit sphere S^n+1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n+1 are Mobius metric, Mobius form, Mobius second fundamental form and Blaschke tensor. In this paper, we prove the following theorem: Let x : M→S^n+1 (n≥2) be an umbilic free hypersurface in S^n+1 with nonnegative Mobius sectional curvature and with vanishing Mobius form. Then x is locally Mobius equivalent to one of the following hypersurfaces: (i) the torus S^k(a) × S^n-k(√1- a^2) with 1 ≤ k ≤ n - 1; (ii) the pre-image of the stereographic projection of the standard cylinder S^k × R^n-k belong to R^n+1 with 1 ≤ k ≤ n- 1; (iii) the pre-image of the stereographic projection of the Cone in R^n+1 : -↑x(u, v, t) = (tu, tv), where (u,v, t)∈S^k(a) × S^n-k-1( √1-a^2)× R^+.