Primeness and primitivity conditions for twisted group $C^*$-algebras
  For a multiplier (2-cocycle) $\sigma$ on a discrete group $G$ we give conditions for which the twisted group $C^*$-algebra associated with the pair $(G,\sigma)$ is prime or primitive. We also discuss how these conditions behave on direct products and free products of groups. 
Tron Omland
math.OA math.GR