The spread of a finite group

• 成果类型: Article
• 署名作者: Burness, Timothy C.; Guralnick, Robert M.; Harper, Scott
• 刊物名称: ANNALS OF MATHEMATICS
• ISSN/ISSBN: 0003-486X
• DOI: 10.4007/annals.2021.193.2.5
• 发表日期: 2021
• 页码: 619-687
• 关键词: fixed-point ratios; maximal-subgroups; exceptional groups; lie type; probabilistic generation; irreducible characters; conjugacy classes; classical-groups; chevalley-groups; uniform spread

摘要

A group G is said to 3/2-generated if every nontrivial element belongs to a generating pair. It is easy to see that if G has this property, then every proper quotient of G is cyclic. In this paper we prove that the converse is true for finite groups, which settles a conjecture of Breuer, Guralnick and Kantor from 2008. In fact, we prove a much stronger result, which solves a problem posed by Brenner and Wiegold in 1975. Namely, if G is a finite group and every proper quotient of G is cyclic, then for any pair of nontrivial elements x(1), x(2) is an element of G, there exists y is an element of G such that G = < x(1), y > = < x(2), y >. In other words, s(G) >= 2, where s(G) is the spread of G. Moreover, if u(G) denotes the more restrictive uniform spread of G, then we can completely characterise the finite groups G with u(G) = 0 and u(G) = 1. To prove these results, we first establish a reduction to almost simple groups. For simple groups, the result was proved by Guralnick and Kantor in 2000 using probabilistic methods, and since then the almost simple groups have been the subject of several papers. By combining our reduction theorem and this earlier work, it remains to handle the groups with socle an exceptional group of Lie type, and this is the case we treat in this paper.