Rational discrete cohomology for totally disconnected locally compact groups

Abstract

Rational discrete cohomology and homology for a totally disconnected locally compact group $G$ is introduced and studied. The $\mathrm{Hom}$-$\otimes$ identities associated to the rational discrete bimodule $\mathrm{Bi}(G)$ allow to introduce the notion of rational duality groups in analogy to the discrete case. It is shown that semi-simple groups defined over a non-discrete, non-archimedean local field are rational t.d.l.c. duality groups, and the same is true for certain topological Kac-Moody groups. However, Y. Neretin's group of spheromorphisms of a locally finite regular tree is not even of finite rational discrete cohomological dimension. For a unimodular t.d.l.c. group $G$ of type $\mathrm{FP}$ it is possible to define an Euler-Poincaré characteristic $\chi (G)$ which is a rational multiple of a Haar measure. This value is calculated explicitly for Chevalley groups defined over a non-discrete, non-archimedean local field $K$ and some other examples.

References in corpus (3)

• Tidy subgroups for commuting automorphisms of totally disconnected groups: an analogue of simultaneous triangularisation of matrices
• Rational discrete cohomology for totally disconnected locally compact groups
• Topological simplicity, commensurator super-rigidity and non-linearities of Kac-Moody groups

Cited by in corpus (7)

• Rational discrete cohomology for totally disconnected locally compact groups
• Finiteness properties of totally disconnected locally compact groups
• Rational discrete first degree cohomology for totally disconnected locally compact groups
• Subgroups, hyperbolicity and cohomological dimension for totally disconnected locally compact groups
• Homotopical Algebra in Categories with Enough Projectives
• On homological properties of the Schlichting completion
• Classifying rational G-spectra for profinite G