Almost cyclic elements in cross-characteristic representations of finite groups of Lie type

Abstract

Abstract This paper is a significant contribution to a general programme aimed to classify all projective irreducible representations of finite simple groups over an algebraically closed field, in which the image of at least one element is represented by an almost cyclic matrix (that is, a square matrix M of size n over a field 𝔽 {\mathbb{F}} with the property that there exists α ∈ 𝔽 {\alpha\in\mathbb{F}} such that M is similar to diag ⁡ ( α ⋅ Id k , M 1 ) {\operatorname{diag}(\alpha\cdot\mathrm{Id}_{k},M_{1})} , where M 1 {M_{1}} is cyclic and 0 ≤ k ≤ n {0\leq k\leq n} ). While a previous paper dealt with the Weil representations of finite classical groups, which play a key role in the general picture, the present paper provides a conclusive answer for all cross-characteristic projective irreducible representations of the finite quasi-simple groups of Lie type and their automorphism groups.