Published online by Cambridge University Press: 24 October 2008
A unital C*-algebra is said to satisfy the Dixmier property if for each element x in
the closed convex hull of all elements of the form u*xu, u being a unitary in
, intersects the centre of
((2), 2·7). The von Neumann algebras and also some other classes of C*-algebras are known to satisfy the Dixmier property (cf. (2), (3), (4), (6)). If
is a simple C*-algebra which satisfies the Dixmier property then
has at most one tracial state. In (3) Archbold raised the question whether there exists a unital simple C*-algebra which has at most one tracial state without satisfying the Dixmier property. In the present note we characterize the unital simple C*-algebras with at most one tracial state in terms of a condition which is similar to the Dixmier property, but is in fact formally weaker in the framework of simple C*-algebras. This characterization relies on the method used by Pedersen in (5) in order to show that for a unital simple C*-algebra
which has at most one tracial state and at least one non-trivial projection the linear span of all projections in
is dense in
As an application we characterize those unital simple C*-algebras with a unique tracial state which satisfy the Dixmier property.