On projective representations for compact quantum groups

We study actions of compact quantum groups on type I -factors, which may be interpreted as projective representations of compact quantum groups. We generalize to this setting some of Woronowicz’s results concerning Peter–Weyl theory for compact quantum groups. The main new phenomenon is that for general compact quantum groups (more precisely, those which are not of Kac type), not all irreducible projective representations have to be finite-dimensional. As applications, we consider the theory of projective representations for the compact quantum groups associated with group von Neumann algebras of discrete groups, and consider a certain non-trivial projective representation for quantum SU(2). © 2011 Elsevier Inc. All rights reserved