On the $C^{\ast }$-algebra associated with the full adele ring of a number field

Abstract

The multiplicative group of a number field acts by multiplication on the full adele ring of the field. Generalising a theorem of Laca and Raeburn, we explicitly describe the primitive ideal space of the crossed product $C^{\ast }$-algebra associated with this action. We then distinguish real, complex, and finite places of the number field using K-theoretic invariants. Combining these results with a recent rigidity theorem of the authors implies that any $\ast$-isomorphism between two such $C^{\ast }$-algebras gives rise to an isomorphism of the underlying number fields that is constructed from the $\ast$-isomorphism.