中文

Area comparison results for isotropic surfaces

微分几何 2007-05-23 v5 辛几何

摘要

Consider a 2-plane PCnP \subset \mathbb{C}^n and let DD be a bounded region in PP with a piecewise-smooth boundary. Let I(D)I(D) be the infimum of areas of all piecewise-smooth isotropic surfaces in Cn\mathbb{C}^n with the same boundary as DD. Then I(D)=λPnArea(D)I(D)= \lambda_P^n \cdot Area(D). If PP is not complex, λPn<3π22\lambda_P^n < \frac{3\pi}{2\sqrt{2}}. For a complex plane CCn\mathbb{C} \subset \mathbb{C}^n, λCn2\lambda_{\mathbb{C}}^n \geq 2, λC23\lambda_{\mathbb{C}}^2 \geq 3 and also 3π222\frac{3\pi^2}{2\sqrt{2}} is the area of an explicit Hamiltonian stationary isotropic Mobius band embedded in Cn\mathbb{C}^n whose boundary is a unit circle in C\mathbb{C}. As a corollary, a compact surface Σ\Sigma (possibly with boundary) in a symplectic manifold can be approximated by isotropic surfaces of area 3π22Area(Σ)\leq \frac{3\pi}{2\sqrt{2}} Area(\Sigma). Another corollary is that a closed curve of length ll in Cn\mathbb{C}^n bounds an isotropic surface of area 3l282\leq \frac{3l^2}{8\sqrt{2}}. A related result is the following: consider CP1CPn\mathbb{C}P^1 \subset \mathbb{C}P^n and let DD be a region in CP1\mathbb{C}P^1. Let I(D)I(D) be the infimum of areas of all isotropic surfaces in CPn\mathbb{C}P^n with the same boundary as DD representing the same relative homology class mod 2 as DD. Then 2Area(D)I(D)λCnArea(D) 2 \cdot Area(D) \leq I(D) \leq \lambda_{\mathbb{C}}^n \cdot Area(D). Moreover the first inequality becomes an equality for D=CP1D=\mathbb{C}P^1.

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引用

@article{arxiv.math/0409293,
  title  = {Area comparison results for isotropic surfaces},
  author = {Edward Goldstein},
  journal= {arXiv preprint arXiv:math/0409293},
  year   = {2007}
}

备注

10 pages