Rigidity and mean curvature flow via harmonic Gauss maps

We investigate properties of harmonic Gauss maps and their applications to Lawson-Osserman’s problem, to the rigidity of space-like submanifolds in a pseudo-Euclidean space and to the mean curvature flow.     

Highly degenerate harmonic mean curvature flow

We study the evolution of a weakly convex surface in with flat sides by the Harmonic Mean Curvature flow. We establish the short time existence as well as the optimal regularity of the surface and we show that the boundaries of the flat sides evolve by the curve shortening flow. It follows from our results that a weakly convex surface with flat sides of class C ^k,γ , for some and 0  <  γ ≤ 1, remains in the same class under the flow. This distinguishes this flow from other, previously studied, degenerate parabolic equations, including the porous medium equation and the Gauss curvature flow with flat sides, where the regularity of the solution for t  >  0 does not depend on the regularity of the initial data. M. C. Caputo partially supported by the NSF grant DMS-03-54639. P. Daskalopoulos partially supported by the NSF grants DMS-01-02252, DMS-03-54639 and the EPSRC in the UK.     

Deforming convex hypersurfaces to a hypersurface with prescribed harmonic mean curvature

A heat flow method is used to deform convex hypersulfaces in a ring domain to a hypersurface whose harmonic mean curvature is a prescribed function.     

Homotopy of area decreasing maps by mean curvature flow

Let f:M→N$f:M\to N$ be a smooth area decreasing map between two Riemannian manifolds (M,_gM)$(M,{\mathrm{g}}_M)$ and (N,_gN)$(N,{\mathrm{g}}_N)$. Under weak and natural assumptions on the curvatures of (M,_gM)$(M,{\mathrm{g}}_M)$ and (N,_gN)$(N,{\mathrm{g}}_N)$, we prove that the mean curvature flow provides a smooth homotopy of f to a constant map.     

L 2 harmonic forms and stability of hypersurfaces with constant mean curvature

We prove that a complete noncompact oriented strongly stable hypersurfaceM ⁿ with cmc (constant mean curvature)H in a complete oriented manifoldN ⁿ⁺¹ with bi-Ricci curvature, satisfying alongM, admits no nontrivialL ² harmonic 1-forms. This implies ifM ⁿ (2n4) is a complete noncompact strongly stable hypersurface in hyperbolic spaceH ⁿ⁺¹(–1) with cmc , there exist no nontrivialL ² harmonic 1-forms onM. We also classify complete oriented strongly stable surfaces with cmcH in a complete oriented manifoldN ³ with scalar curvature satisfying .     

L2调和形式与具有常平均曲率的稳定超曲面

设M为(n 1)维流形Ⅳ中完备、非紧、定向的、具有常平均曲率H的强稳定超曲面,文中证明了若Ⅳ的双Ricci曲率沿M不小于-n^2H^2,则M上不存在非平凡的L^2调和1-形式．     

Time maps and exact multiplicity results for one-dimensional prescribed mean curvature equations

We investigate various properties of time maps for one-dimensional prescribed mean curvature equations. Using these properties, we obtain some exact multiplicity results of positive solutions and sign-changing solutions. As it turned out, these quasilinear problems show many different phenomena from semilinear problems. Our methods are based on a detailed analysis of time maps.     

Hölder continuity of harmonic maps from Riemannian polyhedra to spaces of upper bounded curvature

This is an addendum to the recent Cambridge Tract “Harmonic maps between Riemannian polyhedra”, by J. Eells and the present author. H?lder continuity of locally energy minimizing maps from an admissible Riemannian polyhedron X to a complete geodesic space Y is established here in two cases: (1) Y is simply connected and has curvature (in the sense of A.D. Alexandrov), or (2) Y is locally compact and has curvature , say, and is contained in a convex ball in Y satisfying bi-point uniqueness and of radius (best possible). With Y a Riemannian polyhedron, and in case (2), this was established in the book mentioned above, though with H?lder continuity taken in a weaker, pointwise sense. For X a Riemannian manifold the stated results are due to N.J. Korevaar and R.M. Schoen, resp. T. Serbinowski. Received: 10 October 2001 / Accepted: 20 November 2001 / Published online: 6 August 2002     

Jost maps, ball-homogeneous and harmonic manifolds

Given a real number ε>0, small enough, an associated Jost map J_ε between two Riemannian manifolds is defined. Then we prove that connected Riemannian manifolds for which the center of mass of each small geodesic ball is the center of the ball (i.e. for which the identity is a J_ε map) are ball-homogeneous. In the analytic case we characterize such manifolds in terms of the Euclidean Laplacian and we show that they have constant scalar curvature. Under some restriction on the Ricci curvature we prove that Riemannian analytic manifolds for which the center of mass of each small geodesic ball is the center of the ball are locally and weakly harmonic.