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arXiv 2401.04604math.NTmath.GR
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关于Drinfeld模群的自同构

On the automorphisms of the Drinfeld modular groups

University of Glasgow(格拉斯哥大学);Kongju National University(公州国立大学)

A. W. Mason, Andreas Schweizer

AI总结:

本文研究了Drinfeld模群的自同构结构,发现其自同构群的生成元及作用于极点和椭圆点的特性,并构造了置换孤立顶点的无限阶自同构群。

摘要:

设A是代数函数域K上所有在固定极点∞之外为整数的元素构成的环。与经典的模群SL₂(ℤ)和Bianchi群不同,Drinfeld模群G=GL₂(A)不是可数生成的,其自同构群Aut(G)是不可数的。除了最简单的情况A=𝔽_q[t]外,关于Aut(G)的生成元或其结构知之甚少。我们为一个新的情况找到了Aut(G)的生成元集。在过程中,我们证明了G的每一个自同构都作用于G的极点和椭圆点。推广Reiner对于A=𝔽_q[t]的结果,我们描述了每个极点的一个不可数子群,其在G上的作用本质上由该极点的稳定子群定义。当δ(∞的次数)为1时,椭圆点与商图G\mathcal{T}的孤立顶点有关。我们构造了一个无限阶的G自同构群,该群完全置换孤立顶点并具有循环稳定子群。

英文摘要:

Let $A$ be the ring of elements in an algebraic function field $K$ over $\mathbb{F}_q$ which are integral outside a fixed place $\infty$. In contrast to the classical modular group $SL_2(\mathbb{Z})$ and the Bianchi groups, the {\it Drinfeld modular group} $G=GL_2(A)$ is not finitely generated and its automorphism group $\mathrm{Aut}(G)$ is uncountable. Except for the simplest case $A=\mathbb{F}_q[t]$ not much is known about the generators of $\mathrm{Aut}(G)$ or even its structure. We find a set of generators of $\mathrm{Aut}(G)$ for a new case. \par On the way, we show that {\it every} automorphism of $G$ acts on both, the {\it cusps} and the {\it elliptic points} of $G$. Generalizing a result of Reiner for $A=\mathbb{F}_q[t]$ we describe for each cusp an uncountable subgroup of $\mathrm{Aut}(G)$ whose action on $G$ is essentially defined on the stabilizer of that cusp. In the case where $δ$ (the degree of $\infty$) is $1$, the elliptic points are related to the isolated vertices of the quotient graph $G\setminus\mathcal{T}$ of the Bruhat-Tits tree. We construct an infinite group of automorphisms of $G$ which fully permutes the isolated vertices with cyclic stabilizer.

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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