| Résume | The KK-theory groups with real coefficients can be useful tools to encode certain properties of discrete group actions on C* algebras.
For instance, using the real KK-classes associated to traces on C* algebras, one can rephrase Atiyah’s L2 index theorem for coverings and generalise it to a property of group actions on C*-algebras, which can be called free and properness in K-theory. We will review these constructions and describe related secondary classes.
Based on joint work with Paolo Antonini and Georges Skandalis. |
