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arXiv 1902.07962math.GR
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从局部紧群到离散群的抽象同态

Abstract homomorphisms from locally compact groups to discrete groups

Linus Kramer, Olga Varghese

摘要:

我们证明了从局部紧群$L$到图积$G_Γ$的每个抽象同态$φ$,如果赋予离散拓扑,要么是连续的,要么是$φ(L)$位于一个“小”抛物子群中.特别地,图不是“小”的图积上的每个局部紧群拓扑是离散的。这扩展了莫里斯-尼古拉斯早期的工作。我们还展示了以下内容。若$L$是局部紧群,且$G$是不含无限扭群和无限生成阿贝尔群的离散群,则每个抽象同态$φ:L\to G$要么是连续的,要么是$φ(L)$包含在$G$的有限非平凡子群的正规化子中.作为应用,我们得到了关于从局部紧群到Artin群和Coxeter群的同态连续性的结果。

英文摘要:

We show that every abstract homomorphism $φ$ from a locally compact group $L$ to a graph product $G_Γ$, endowed with the discrete topology, is either continuous or $φ(L)$ lies in a 'small' parabolic subgroup. In particular, every locally compact group topology on a graph product whose graph is not 'small' is discrete. This extends earlier work by Morris-Nickolas. We also show the following. If $L$ is a locally compact group and if $G$ is a discrete group which contains no infinite torsion group and no infinitely generated abelian group, then every abstract homomorphism $φ:L\to G$ is either continuous, or $φ(L)$ is contained in the normalizer of a finite nontrivial subgroup of $G$. As an application we obtain results concerning the continuity of homomorphisms from locally compact groups to Artin and Coxeter groups.

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