Technion Mathematics Colloquium Speaker: Andrzej Zuk (Paris 7) Title: On a problem of Atiyah Time: Monday, January 16, 3:30 pm Place: Amado 232, Technion Colloquium homepage: <http://www.technion.ac.il/~yehuday/colloquium/colloq.html> Abstract: In 1976, Michael Atiyah defined L2-Betti numbers for manifolds and asked a question about their rationality. These numbers arise as the von Neumann dimensions of kernels of certain operators acting on the L2-space of the fundamental group of a manifold. The problem concerning their values is closely related to the Kaplansky zero-divisor question. We present constructions of closed manifolds with irrational L2-Betti numbers. --------------------------------------------------------- Technion Math. Net (TECHMATH) Editor: Michael Cwikel <techm@math.technion.ac.il> Announcement from: Amir Yehudayoff <amir.yehudayoff@gmail.com>