Field Embeddings which are conjugate under a unit of a p-adic classical Group

TL;DR

This paper investigates conditions under which conjugate field extensions within a p-adic classical group can be realized through elements stabilizing a point in the Bruhat-Tits building, extending understanding of conjugacy in unitary groups.

Contribution

It establishes criteria for conjugacy of field extensions in p-adic unitary groups via stabilizer elements, linking Bruhat-Tits building points to conjugation properties.

Findings

E1 and E2 are conjugate under a stabilizer element if they are conjugate under the automorphism group and a certain condition holds.

Conjugation by g can often be realized within the stabilizer of a point in the group, not just the automorphism group.

The results apply to Hermitian spaces over division algebras with specific index and residue characteristic conditions.

Abstract

Let (V,h) be a Hermitian space over a division algebra D which is of index at most two over a non-Archimedean local field k of residue characteristic not 2. Let G be the unitary group defined by h and let \sigma be the adjoint involution. Suppose we are given two \sigma-invariant but not \sigma-fixed field extensions E1 and E2 of k in End_D(V) which are isomorphic under conjugation by an element g of G and suppose that there is a point x in the Bruhat-Tits building of G which is fixed by the action of E1\{0} and E2\{0} on the reduced building of Aut_D(V). Then E1 is conjugate to E2 under an element of the stabilizer of x in G if E1 and E2 are conjugate under an element of the stabilizer of x in Aut_D(V) and a weak extra condition. In addition in many cases the conjugation by g from E1 to E2 can be realized as conjugation by an element of the stabilizer of x in G.