Controlled K-theory for groupoids & applications to Coarse Geometry

Abstract

We develop a generalization of quantitative K-theory, which we call controlled K-theory. It is powerful enough to study the K-theory of crossed product of C⁎-algebras by action of étale groupoids and discrete quantum groups. In this article, we will use it to study groupoids crossed products. We define controlled assembly maps, which factorize the Baum–Connes assembly maps, and define the controlled Baum–Connes conjecture. We relate the controlled conjecture for groupoids to the classical conjecture, and to the coarse Baum–Connes conjecture. This allows to give applications to Coarse Geometry. In particular, we can prove that the maximal version of the controlled coarse Baum–Connes conjecture is satisfied for a coarse space which admits a fibred coarse embedding, which is a stronger version of a result of M. Finn-Sell.