圆盘微分同胚的导数映射:一个例子
The derivative map for diffeomorphism of disks: An example
AI总结:
本文证明圆盘微分同胚的导数映射在 $k=11$ 时于同伦群上诱导非零映射,并据此给出 Burghelea–Lashof 猜想的反例。
摘要:
我们证明,通过对微分同胚取导数所定义的导数映射 $d \colon \mathrm{Diff}_\partial(D^k) \to Ω^kSO_k$,能够在同伦群上诱导出非平凡映射。具体而言,对于 $k=11$,我们证明以下同态非零:$d_* \colon π_5\mathrm{Diff}_\partial(D^{11}) \to π_5Ω^{11}SO_{11} \cong π_{16}SO_{11}$。作为推论,我们给出了 Burghelea 和 Lashof 一个猜想的反例,从而给出球面上一个非平凡向量丛 $E$ 的例子,而它作为拓扑 $\mathbb{R}^k$-丛是平凡的($E$ 的秩为 $k=11$,底球面为 $S^{17}$)。证明依赖于 Burklund 和 Sencer 关于界定哪些同伦 17-球面以 8-连通流形为边界的最新结果、Antonelli、Burghelea 和 Kahn 对 Gromoll 滤过采用的 plumbbing 方法,以及某些同伦球面低余维嵌入的显式构造。
英文摘要:
We prove that the derivative map $d \colon \mathrm{Diff}_\partial(D^k) \to Ω^kSO_k$, defined by taking the derivative of a diffeomorphism, can induce a nontrivial map on homotopy groups. Specifically, for $k = 11$ we prove that the following homomorphism is non-zero: $$ d_* \colon π_5\mathrm{Diff}_\partial(D^{11}) \to π_{5}Ω^{11}SO_{11} \cong π_{16}SO_{11} $$ As a consequence we give a counter-example to a conjecture of Burghelea and Lashof and so give an example of a non-trivial vector bundle $E$ over a sphere which is trivial as a topological $\mathbb{R}^k$-bundle (the rank of $E$ is $k=11$ and the base sphere is $S^{17}$.) The proof relies on a recent result of Burklund and Senger which determines those homotopy 17-spheres bounding $8$-connected manifolds, the plumbing approach to the Gromoll filtration due to Antonelli, Burghelea and Kahn, and an explicit construction of low-codimension embeddings of certain homotopy spheres.
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