Faithful tracial states on quotients of C*-algebras

Abstract

We study the existence of faithful tracial states on C * -algebras as well as the stronger proerty that all quotients admit faithful tracial states. We provide a sufficient and necessary condition for when C * -algebras admit faithful tracial states in terms of the Cuntz semigroup and use this to give an equivalent formulation for all quotients to admit faithful tracial states. We relate this to the notion of strong quasidiagonality, and show that any amenable discrete group with faithful tracial states on all quotients of the corresponding group-C * -algebra is strongly quasidiagonal under the condition that all quotients satisfy the Universal Coefficient Theorem.