Memoirs of the American Mathematical Society Series

$Cover of Finite Groups Which Are Almost Groups of Lie Type in Characteristic $\mathbf {p}$$

Finite Groups Which Are Almost Groups of Lie Type in Characteristic $\mathbf {p}$

by Chris Parker, Gerald Pientka, Andreas Seidel, and Gernot Stroth

Published 31 January 2024

Let p be a prime. In this paper we investigate finite K{2,p}-groups G which have a subgroup H ? G such that K ? H = NG(K) ? Aut(K) for K a simple group of Lie type in characteristic p, and |G : H| is coprime to p. If G is of local characteristic p, then G is called almost of Lie type in characteristic p. Here G is of local characteristic p means that for all nontrivial p-subgroups P of G, and Q the largest normal p-subgroup in NG(P) we have the containment CG(Q) ? Q. We determine details of the structure of groups which are almost of Lie type in characteristic p. In particular, in the case that the rank of K is at least 3 we prove that G = H. If H has rank 2 and K is not PSL3(p) we determine all the examples where G = H. We further investigate the situation above in which G is of parabolic characteristic p. This is a weaker assumption than local characteristic p. In this case, especially when p ? {2, 3}, many more examples appear. In the appendices we compile a catalogue of results about the simple groups with proofs. These results may be of independent interest.