Group C*-Algebras and K-theory ¡ Nigel Higson and Erik Guentner ¢ Department of Mathematics, Pennsylvania State University University Park, PA 16802
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[email protected] Preface These notes are about the formulation of the Baum-Connes conjecture in operator algebra theory and the proofs of some cases of it. They are aimed at readers who ¤ have some prior familiarity with -theory for ¥§¦ -algebras (up to and including the Bott Periodicity theorem). I hope the notes will be suitable for a second course in operator ¤ -theory. The lectures begin by reviewing ¤ -theory and the Bott periodicity theorem. Much of the Baum-Connes theory has to do with broadening the periodicity theo- rem in one way or another, and for this reason quite some time is spent formulating and proving the theorem in a way which is suited to later extensions. Following that, the lectures turn to the machinery of bivariant ¤ -theory and the formulation of the Baum-Connes conjecture. The main objective of the notes is reached in Lec- ture 4, where the conjecture is proved for groups which act properly and isometrically on affine Euclidean spaces. The remaining lectures deal with partial results which are important in applications and with counterxamples to various overly optimistic strengthenings of the conjecture. Despite their length the notes are not complete in every detail, and the reader will have to turn to the references, or his own inner resources, to fill some gaps. In ad- dition the lectures contain no discussion of applications or connections to geometry, topology and harmonic analysis, nor do they cover the remarkable work of Vincent Lafforgue.