Dixmier Traces and Unitary Representations

As is known, for any two given unitary representations of a topological group in Hilbert spaces, a new unitary representation in the corresponding space of Hilbert–Schmidt mappings can be defined. In the paper, a modification of this construction is suggested that uses the Dixmier trace (instead of the ordinary operator trace). The case of the group of second-order real unimodular matrices is studied in detail.