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arXiv math/0702625math.DGmath.GT
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曲线清管器的最小值-最大值

Min-max for sweepouts by curves

Tobias H. Colding, William P. Minicozzi

摘要:

给定2-球面上的一个黎曼度量,通过一个连续的单参数闭曲线族从点曲线开始和结束,将2-球面扫出。以连续的方式,尽可能地拉紧每个曲线,同时保持清料,从而拉紧清料。我们证明了以下有用的性质(见下面的定理1.9); cf. [CM1]、[CM 2]、[CD]的命题3.1、[Pi]的命题3.1和[Al]的命题12.5:收紧的扫掠中的长度接近扫掠中最长曲线的长度的每条曲线本身必须接近闭测地线。特别是,在扫掠中存在接近于闭测地线的曲线。利用扫掠法在2-球面上寻找闭测地线的方法可以追溯到20世纪20年代的伯克霍夫。上述有用的财产几乎总是隐含在任何sweepout建设的临界点的变分问题,但它并不总是记录,因为大多数作者只感兴趣的存在一个临界点。类似的结果也适用于2-球而不是圆的扫掠;参见。\cite{CM2}。在这两种情况下,想法基本上是相同的,尽管对于没有能量集中的曲线(即,"bubbling“); cf. \cite{Jo}。

英文摘要:

Given a Riemannian metric on the 2-sphere, sweep the 2-sphere out by a continuous one-parameter family of closed curves starting and ending at point curves. Pull the sweepout tight by, in a continuous way, pulling each curve as tight as possible yet preserving the sweepout. We show the following useful property (see Theorem 1.9 below); cf. [CM1], [CM2], proposition 3.1 of [CD], proposition 3.1 of [Pi], and 12.5 of [Al]: Each curve in the tightened sweepout whose length is close to the length of the longest curve in the sweepout must itself be close to a closed geodesic. In particular, there are curves in the sweepout that are close to closed geodesics. Finding closed geodesics on the 2-sphere by using sweepouts goes back to Birkhoff in the 1920s. The above useful property is virtually always implicit in any sweepout construction of critical points for variational problems yet it is not always recorded since most authors are only interested in the existence of one critical point. Similar results holds for sweepouts by 2-spheres instead of circles; cf. \cite{CM2}. The ideas are essentially the same in the two cases, though technically easier for curves where there is no concentration of energy (i.e., ``bubbling''); cf. \cite{Jo}.

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