Assembly maps for topological cyclic homology of group algebras

Abstract

We use assembly maps to study TC.AŒG I p/, the topological cyclic homology at a prime p of the group algebra of a discrete group G with coefficients in a connective ring spectrum A. For any finite group, we prove that the assembly map for the family of cyclic subgroups is an isomorphism on homotopy groups. For infinite groups, we establish pro-isomorphism, (split) injectivity, and rational injectivity results, as well as counterexamples to injectivity and surjectivity. In particular, for hyperbolic groups and for virtually finitely generated abelian groups, we show that the assembly map for the family of virtually cyclic subgroups is injective but in general not surjective.