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arXiv 1610.04098math.GTmath.DSmath.GR
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圆上群作用的灵活性

Flexibility of group actions on the circle

Sang-hyun Kim, Thomas Koberda, Mahan Mj

摘要:

在这部分简要的专着,我们制定了一个一般框架,生产不可数家庭的异国情调的行动,某些经典的研究团体的行动圈。我们表明,如果$L$是一个非平凡的极限群,那么非线性表示品种$\mathrm{Hom}(L,\mathrm{Homeo}_+(S^1))$包含不可数许多半共轭类的忠实行动$S^1$与成对不相交的旋转谱(除了$0$),使每个表示升降机$\mathbb{R}$。对于大多数Fuchsian群$L$,我们进一步证明了这种柔性现象甚至局部发生,从而补充了K.曼恩我们证明了每个非初等的自由或曲面群都承认$S^1$上的一个作用,该作用与通过$\mathrm{Homeo}_+(S^1)$中的有限维连通李群分解的任何作用都不半共轭。证明了有界曲面的映射类群在$S^1$上具有非半共轭忠实作用。在建立这些结果的过程中,我们证明了$\mathrm{PSL}_2(\mathbb{R})$的不离散子群的一般组合定理,这些定理适用于大多数Fuchsian群和所有极限群。我们还显示了一个拓扑鲍姆斯拉格引理,和一般的组合定理表示成Baire拓扑群。这些群上的$\mathbb{Z}$ -值次可加亏损-1拟同构的丰度将作为推论而遵循。我们还给出了一个大多是自包含的和解的各种概念的半共轭在现存的文献中,通过显示它们都是等价的。

英文摘要:

In this partly expository monograph we develop a general framework for producing uncountable families of exotic actions of certain classically studied groups acting on the circle. We show that if $L$ is a nontrivial limit group then the nonlinear representation variety $\mathrm{Hom}(L,\mathrm{Homeo}_+(S^1))$ contains uncountably many semi-conjugacy classes of faithful actions on $S^1$ with pairwise disjoint rotation spectra (except for $0$) such that each representation lifts to $\mathbb{R}$. For the case of most Fuchsian groups $L$, we prove further that this flexibility phenomenon occurs even locally, thus complementing a result of K. Mann. We prove that each non-elementary free or surface group admits an action on $S^1$ that is never semi-conjugate to any action that factors through a finite--dimensional connected Lie subgroup in $\mathrm{Homeo}_+(S^1)$. It is exhibited that the mapping class groups of bounded surfaces have non-semi-conjugate faithful actions on $S^1$. In the process of establishing these results, we prove general combination theorems for indiscrete subgroups of $\mathrm{PSL}_2(\mathbb{R})$ which apply to most Fuchsian groups and to all limit groups. We also show a Topological Baumslag Lemma, and general combination theorems for representations into Baire topological groups. The abundance of $\mathbb{Z}$--valued subadditive defect--one quasimorphisms on these groups would follow as a corollary. We also give a mostly self-contained reconciliation of the various notions of semi-conjugacy in the extant literature by showing that they are all equivalent.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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