Minimal compact group actions on C∗-algebras with simple fixed point algebras

Abstract

The notion of quasi-product actions of a compact group on a C[Formula: see text]-algebra was introduced by Bratteli et al. in their attempt to seek an equivariant analogue of Glimm’s characterization of non-type I C[Formula: see text]-algebras. We show that a faithful minimal action of a second countable compact group on a separable C[Formula: see text]-algebra is quasi-product whenever its fixed point algebra is simple. This was previously known only for compact abelian groups and for profinite groups. Our proof relies on a subfactor technique applied to finite index inclusions of simple C[Formula: see text]-algebras in the purely infinite case, and also uses ergodic actions of compact groups in the general case. As an application, we show that if moreover the fixed point algebra is a Kirchberg algebra, such an action is always isometrically shift-absorbing, and hence is classifiable by the equivariant KK-theory due to a recent result of Gabe-Szabó.