1. Embeddings of local fields in simple algebras and simplicial structures
- Author
-
Daniel Skodlerack
- Subjects
Discrete mathematics ,simple algebras ,non-archimedean local fields ,General Mathematics ,Non-archimedean local fields ,Coxeter group ,17C20 ,Type (model theory) ,Centralizer and normalizer ,buildings ,Cyclic permutation ,Combinatorics ,Field extension ,Simple algebras ,Division algebra ,Embeddings types ,Embedding ,20E42 ,Isomorphism ,12J25 ,Buildings ,Mathematics::Representation Theory ,Mathematics - Abstract
We give a geometric interpretation of Broussous-Grabitz embedding types. We fix a central division algebra $D$ of finite index over a non-Archimedean local field $F$ and a positive integer $m$. Further we fix a hereditary order $\mathfrak{a}$ of $\operatorname{M}_m(D)$ and an unramified field extension $E|F$ in $\operatorname{M}_m(D)$ which is embeddable in $D$ and which normalizes $\mathfrak{a}$. Such a pair $(E,\mathfrak{a})$ is called an embedding. The embedding types classify the $\operatorname{GL}_m(D)$-conjugation classes of these embeddings. Such a type is a class of matrices with non-negative integer entries. We give a formula which allows us to recover the embedding type of $(E,\mathfrak{a})$ from the simplicial type of the image of the barycenter of $\mathfrak{a}$ under the canonical isomorphism, from the set of $E^\times$-fixed points of the reduced building of $\operatorname{GL}_m(D)$ to the reduced building of the centralizer of $E^\times$ in $\operatorname{GL}_m(D)$. Conversely the formula allows to calculate the simplicial type up to cyclic permutation of the Coxeter diagram.
- Published
- 2021