THE BOHR COMPACTIFICATION OF AN ARITHMETIC GROUP - Archive ouverte HAL Access content directly
Preprints, Working Papers, ... (Preprint) Year : 2023

THE BOHR COMPACTIFICATION OF AN ARITHMETIC GROUP

Abstract

Given a group Γ, its Bohr compactification Bohr(Γ) and its profinite completion Prof(Γ) are compact groups naturally associated to Γ; moreover, Prof(Γ) can be identified with the quotient of Bohr(Γ) by its connected component Bohr(Γ)_0. We study the structure of Bohr(Γ) for an arithmetic subgroup Γ of an algebraic group G over Q. When G is unipotent, we show that Bohr(Γ) can be identified with the direct product Bohr(Γ/[Γ,Γ])_0 × Prof(Γ). In the general case, using a Levi decomposition G = U ⋊ H (where U is unipotent and H is reductive), we show that Bohr(Γ) can be described as the semi-direct product of a certain quotient of Bohr(Γ ∩ U) with Bohr(Γ ∩ H). When G is simple and has higher R-rank, Bohr(Γ) is isomorphic, up to a finite group, to the product K × Prof(Γ), where K is the maximal compact factor of G(R).
Fichier principal
Vignette du fichier
BohrCompactficationArithmeticGroup.pdf (433.52 Ko) Télécharger le fichier
Origin : Files produced by the author(s)

Dates and versions

hal-04073352 , version 1 (18-04-2023)

Identifiers

  • HAL Id : hal-04073352 , version 1

Cite

Bachir Bekka. THE BOHR COMPACTIFICATION OF AN ARITHMETIC GROUP. 2023. ⟨hal-04073352⟩
16 View
24 Download

Share

Gmail Facebook X LinkedIn More