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arXiv math/0512547math.DGmath.MG
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海森堡群H^1中的面积平稳曲面

Area-stationary surfaces in the Heisenberg group H^1

Manuel Ritoré, César Rosales

摘要:

我们用变分的方法引入了海森堡群H ^1中曲面的中曲率的概念,并赋予了它的卡诺-卡拉西奥多里距离。通过分析面积的一阶变分,我们将面积上的C^2平稳曲面刻画为中曲率零(或在保体积条件下为常数)且特征曲线与奇异曲线正交的曲面。此外,对于包围给定区域的保体积面积平稳曲面,得到了一个与面积、中曲率和体积有关的Minkowski型公式.由于面积平稳曲面的特征,我们改进了以前的伯恩斯坦型定理,以便描述H^1中xy平面上的整个面积平稳图。校准参数表明,这些图是全球面积最小化。最后,利用已知的奇异集的描述、面积平稳曲面的特征和常中曲率曲面的规则性质,证明了我们的主要结果,其中我们将H^1中的保体积面积平稳曲面分类为非空奇异集.特别地,我们在欧几里得空间中推导出亚历山德罗夫唯一性定理的对应定理:在体积约束下,H^1区域平稳的任何紧致连通C^2曲面必须与旋转对称球面全等,该旋转对称球面是连接两点的所有曲率相同的测地线的并集。作为结果,我们解决了H^1中的等周问题,假设解是C^2光滑的。

英文摘要:

We use variational arguments to introduce a notion of mean curvature for surfaces in the Heisenberg group H^1 endowed with its Carnot-Carathéodory distance. By analyzing the first variation of area, we characterize C^2 stationary surfaces for the area as those with mean curvature zero (or constant if a volume-preserving condition is assumed) and such that the characteristic curves meet orthogonally the singular curves. Moreover, a Minkowski type formula relating the area, the mean curvature, and the volume is obtained for volume-preserving area-stationary surfaces enclosing a given region. As a consequence of the characterization of area-stationary surfaces, we refine previous Bernstein type theorems in order to describe entire area-stationary graphs over the xy-plane in H^1. A calibration argument shows that these graphs are globally area-minimizing. Finally, by using the known description of the singular set, the characterization of area-stationary surfaces, and the ruling property of constant mean curvature surfaces, we prove our main results where we classify volume-preserving area-stationary surfaces in H^1 with non-empty singular set. In particular, we deduce the following counterpart to Alexandrov uniqueness theorem in Euclidean space: any compact, connected, C^2 surface in H^1 area-stationary under a volume constraint must be congruent with a rotationally symmetric sphere obtained as the union of all the geodesics of the same curvature joining two points. As a consequence, we solve the isoperimetric problem in H^1 assuming C^2 smoothness of the solutions.

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