Deformation of algebras associated with group cocycles

We study deformation of algebras with coaction symmetry of reduced algebras of dis-crete groups, where the deformation parameter is given by a continuous family of group 2-cocycles. When the group satisfies the Baum-Connes conjecture with coefficients, we obtain an isomor-phism of K-groups of the deformed algebras. This extends both the theta-deformation of Rieffel on Tn-actions, and a recent result of Echterhoff, Luck, Phillips, and Walters on the K-groups on the twisted group algebras.