p-stable group

In finite group theory, a p-stable group for an odd prime p is a finite group satisfying a technical condition introduced by Gorenstein and Walter (1964, p.169, 1965) in order to extend Thompson's uniqueness results in the odd order theorem to groups with dihedral Sylow 2-subgroups.

Definitions

There are several equivalent definitions of a p-stable group.

First definition.

We give definition of a p-stable group in two parts. The definition used here comes from (Glauberman 1968, p. 1104).

1. Let p be an odd prime and G be a finite group with a nontrivial p-core $O_p(G)$. Then G is p-stable if it satisfies the following condition: Let P be an arbitrary p-subgroup of G such that $O_{p^\prime}(G)$ is a normal subgroup of G. Suppose that $x\in N_G(P)$ and $\bar x$ is the coset of $C_G(P)$ containing x. If $[P,x,x]=1$, then $\overline{x}\in O_n(N_G(P)/C_G(P))$.

Now, define $\mathcal{M}_p(G)$ as the set of all p-subgroups of G maximal with respect to the property that $O_p(M)\not= 1$.

2. Let G be a finite group and p an odd prime. Then G is called p-stable if every element of $\mathcal{M}_p(G)$ is p-stable by definition 1.

Second definition.

Let p be an odd prime and H a finite group. Then H is p-stable if $F^*(H)=O_p(H)$ and, whenever P is a normal p-subgroup of H and $g \in H$ with $[P,g,g]=1$, then $gC_H(P)\in O_p(H/C_H(P))$.

Properties

If p is an odd prime and G is a finite group such that SL₂(p) is not involved in G, then G is p-stable. If furthermore G contains a normal p-subgroup P such that $C_G(P)\leqslant P$, then $Z(J_0(S))$ is a characteristic subgroup of G, where $J_0(S)$ is the subgroup introduced by John Thompson in (Thompson 1969, pp. 149–151).

See also

• p-stability is used as one of the conditions in Glauberman's ZJ theorem.
• Quadratic pair
• p-constrained group
• p-solvable group

References

• Glauberman, George (1968), "A characteristic subgroup of a p-stable group", Canadian Journal of Mathematics 20: 1101–1135, doi:10.4153/cjm-1968-107-2, ISSN 0008-414X, MR 0230807
• Thompson, John G. (1969), "A replacement theorem for p-groups and a conjecture", Journal of Algebra 13: 149–151, doi:10.1016/0021-8693(69)90068-4, ISSN 0021-8693, MR 0245683
• Gorenstein, D.; Walter, John H. (1964), "On the maximal subgroups of finite simple groups", Journal of Algebra 1: 168–213, doi:10.1016/0021-8693(64)90032-8, ISSN 0021-8693, MR 0172917
• Gorenstein, D.; Walter, John H. (1965), "The characterization of finite groups with dihedral Sylow 2-subgroups. I", Journal of Algebra 2: 85–151, doi:10.1016/0021-8693(65)90027-X, ISSN 0021-8693, MR 0177032
• Gorenstein, D.; Walter, John H. (1965), "The characterization of finite groups with dihedral Sylow 2-subgroups. II", Journal of Algebra 2 (2): 218–270, doi:10.1016/0021-8693(65)90019-0, ISSN 0021-8693, MR 0177032
• Gorenstein, D.; Walter, John H. (1965), "The characterization of finite groups with dihedral Sylow 2-subgroups. III", Journal of Algebra 2 (3): 354–393, doi:10.1016/0021-8693(65)90015-3, ISSN 0021-8693, MR 0190220
• Gorenstein, D. (1979), "The classification of finite simple groups. I. Simple groups and local analysis", American Mathematical Society. Bulletin. New Series 1 (1): 43–199, doi:10.1090/S0273-0979-1979-14551-8, ISSN 0002-9904, MR 513750
• Gorenstein, D. (1980), Finite groups (2nd ed.), New York: Chelsea Publishing Co., ISBN 978-0-8284-0301-6, MR 569209