Noncommutative coarse geometry

Abstract

We use compactifications of C\*-algebras to introduce noncommutative coarse geometry. We transfer a noncommutative coarse structure on a C\*-algebra with an action of a locally compact Abelian group by translations to Rieffel deformations and prove that the resulting noncommutative coarse spaces are coarsely equivalent. We construct a noncommutative coarse structure from a cocompact continuously square-integrable action of a group and show that this is coarsely equivalent to the standard coarse structure on the group in question. We define noncommutative coarse maps through certain completely positive maps that induce \*-homomorphisms on the boundaries of the compactifications. We lift \*-homomorphisms between separable, nuclear boundaries to noncommutative coarse maps and prove an analogous lifting theorem for maps between metrisable boundaries of ordinary locally compact spaces.