Embedding permutation groups into wreath products in product action

TL;DR

This paper studies how subgroups of wreath products acting on functions can be embedded into smaller or direct product structures, with applications to error-correcting codes in Hamming graphs.

Contribution

It provides a new embedding theorem for subgroups of wreath products in product action, depending on their action on the set Delta.

Findings

Subgroups can be embedded into smaller wreath products if the action is transitive.

Intransitive actions lead to embeddings into direct products of wreaths.

Applications to automorphism groups of graph products and codes.

Abstract

The wreath product of two permutation groups G < Sym(Gamma) and H < Sym(Delta) can be considered as a permutation group acting on the set Pi of functions from Delta to Gamma. This action, usually called the product action, of a wreath product plays a very important role in the theory of permutation groups, as several classes of primitive or quasiprimitive groups can be described as subgroups of such wreath products. In addition, subgroups of wreath products in product action arise as automorphism groups of graph products and codes. In this paper we consider subgroups X of full wreath products Sym(Gamma) wr Sym(Delta) in product action. Our main result is that, in a suitable conjugate of X, the subgroup of Sym(Gamma) induced by a stabilizer of a coordinate delta in Delta only depends on the orbit of delta under the induced action of X on Delta. Hence, if the action of X on Delta is transitive, then X can be embedded into a much smaller wreath product. Further, if this X-action is intransitive, then X can be embedded into a direct product of such wreath products where the factors of the direct product correspond to the X-orbits in Delta. We offer an application of the main theorems to error-correcting codes in Hamming graphs.