Group actions on C*-algebras and their description by Hilbert C*-extensions

Automorphism groups #GAMMA# of C*-algebras A are considered, where #gamma#_1 x #gamma#_2 and #gamma#_2 x #gamma#_1 are unitarily equivalent for all #gamma#_1, #gamma#_2 element of #GAMMA#. The paper discusses the problem of the existence of Hilbert C*-extensions #left brace#F, #alpha#(G)#right brace# of #left brace#A, #GAMMA##right brace#, in particular its cohomological aspect. If the center Z subset or equal A of A is trivial, Z=C1, then this problem is a special case (the abelian or automorphism case) of the Doplicher-Roberts duality theory for compact groups. Special cases with Z contains C1 are presented, where the existence of Hilbert-C*-extensions can be proved. (orig.)SIGLEAvailable from TIB Hannover: RR 1596(385) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman