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arXiv 1306.4087math.SG
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Legendre变换在余切丛Floer复形研究中的作用

The role of the Legendre transform in the study of the Floer complex of cotangent bundles

Alberto Abbondandolo, Matthias Schwarz

摘要:

考虑闭可定向流形M的余切丛T*M上的经典哈密顿量H,设L:TM -> R是它的Legendre-对偶拉格朗日量.在以前的文章中,我们构造了一个同构Phi从Morse复的拉格朗日作用泛函,这是与L的Floer复,这是确定的H。本文给出了Φ的一个同伦逆Psi的显式构造。与其他之前定义的相同方向的映射相反,Psi是链级别的同构,并保留了动作过滤。它的定义是基于计数Floer轨迹上的负半圆柱的边界上满足“一半”的哈密顿方程。虽然不是拉格朗日型的,这样的边界条件定义的弗雷德霍姆算子具有良好的紧性。我们还提出了一个启发式的论点,独立于任何Fredholm和紧性分析,解释了为什么空间的地图中使用的定义披和PSI是自然的。勒让德变换起着至关重要的作用,在我们的严格和启发式的论点。我们处理了一些细节的微妙问题的方向和显示的同伦的Floer复杂的同构的奇异同调的闭路空间的局部系数系统,这是由拉回TM的第二Stiefel-Whitney类的2-环面在M。

英文摘要:

Consider a classical Hamiltonian H on the cotangent bundle T*M of a closed orientable manifold M, and let L:TM -> R be its Legendre-dual Lagrangian. In a previous paper we constructed an isomorphism Phi from the Morse complex of the Lagrangian action functional which is associated to L to the Floer complex which is determined by H. In this paper we give an explicit construction of a homotopy inverse Psi of Phi. Contrary to other previously defined maps going in the same direction, Psi is an isomorphism at the chain level and preserves the action filtration. Its definition is based on counting Floer trajectories on the negative half-cylinder which on the boundary satisfy "half" of the Hamilton equations. Albeit not of Lagrangian type, such a boundary condition defines Fredholm operators with good compactness properties. We also present a heuristic argument which, independently on any Fredholm and compactness analysis, explains why the spaces of maps which are used in the definition of Phi and Psi are the natural ones. The Legendre transform plays a crucial role both in our rigorous and in our heuristic arguments. We treat with some detail the delicate issue of orientations and show that the homology of the Floer complex is isomorphic to the singular homology of the loop space of M with a system of local coefficients, which is defined by the pull-back of the second Stiefel-Whitney class of TM on 2-tori in M.

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