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arXiv 2111.05697math.GR
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关于有限群的可解图

On the soluble graph of a finite group

Timothy C. Burness, Andrea Lucchini, Daniele Nemmi

摘要:

设$G$是有限不可解群,其根$R(G)$是可解的.在本文中,我们研究的$G$,这是一个自然的推广广泛研究的交换图的可解图。这里的顶点是$G \setminus R(G)$中的元素,如果它们生成$G$的可解子群,则$x$与$y$相邻。我们的主要结果表明,这个图总是连通的,它的直径,表示为$δ_{\mathcal{S}}(G)$,最多是$5$。更确切地说,我们表明,$δ_{\mathcal{S}}(G) \leqslant 3$,如果$G$不是几乎简单的,我们得到更强的界限几乎简单的各种家庭的群体。例如,我们将显示所有$n \geqslant 6$的$δ_{\mathcal{S}}(S_n) = 3$。我们还建立了具有$δ_{\mathcal{S}}(G) \geqslant 4$的单群的存在性。例如,我们证明了$δ_{\mathcal{S}}(A_{2p+1}) \geqslant 4$对于每个苏菲·杰曼素数$p \geqslant 5$,这表明我们的$5$的一般上界接近最佳可能。最后,我们简要讨论了一些变化的可溶性图的建设,我们提出了几个开放的问题。

英文摘要:

Let $G$ be a finite insoluble group with soluble radical $R(G)$. In this paper we investigate the soluble graph of $G$, which is a natural generalisation of the widely studied commuting graph. Here the vertices are the elements in $G \setminus R(G)$, with $x$ adjacent to $y$ if they generate a soluble subgroup of $G$. Our main result states that this graph is always connected and its diameter, denoted $δ_{\mathcal{S}}(G)$, is at most $5$. More precisely, we show that $δ_{\mathcal{S}}(G) \leqslant 3$ if $G$ is not almost simple and we obtain stronger bounds for various families of almost simple groups. For example, we will show that $δ_{\mathcal{S}}(S_n) = 3$ for all $n \geqslant 6$. We also establish the existence of simple groups with $δ_{\mathcal{S}}(G) \geqslant 4$. For instance, we prove that $δ_{\mathcal{S}}(A_{2p+1}) \geqslant 4$ for every Sophie Germain prime $p \geqslant 5$, which demonstrates that our general upper bound of $5$ is close to best possible. We conclude by briefly discussing some variations of the soluble graph construction and we present several open problems.

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