Mercoledì 16 marzo 2011
Aula Dal Passo, Dip. Matematica, U. Roma "Tor Vergata"
Ore 14.00	N. P. Brown , Penn State University - New C*-completions of groups
	Given a group G, there are two common C*-completions of the group algebra: the reduced and full. But there are many other canonical completions determined by "rates of decay" of matrix coefficients. In joint work with Erik Guentner we've started to study these other completions and the results look promising. So far, we've found the first C*-characterization of a-T-menability, given new examples of "exotic" quantum groups, and substantially simplified and generalized a recent theorem of Ron Douglas and Piotr Nowak.
Ore 15.00	V. Capraro Thesis' defence, Università di Roma "Tor Vergata" - Peculiar properties of subfactors of ultrapowers of the hyperfinite II1 factor
	Connes' embedding conjecture asks whether any II1 factor with separable predual embeds into the ultrapower Rω of the hyperfinite II1 factor. Motivated by this problem I start studying peculiar properties of subfactors of Rω. I give new and unexpected examples of subfactors of Rω, for instance the group von Neumann algebra of the unitary group of Rω (joint work with L.Paunescu). I use a new invariant introduced by N.P. Brown in order to give positive answer to the following problem of Sorin Popa: given an embedding into Rω, does there exist another embedding whose relative commutant is a factor? (joint work with N. P. Brown). Finally I introduce a notion of curvature on this invariant that allows to find a geometric counterpart of rigidity: the invariant associated to a factor with property (T) is plenty of angles (joint work with L. Benzo).
Ore 16.00	Coffee Break
Ore 16.30	G. Arzhantseva, Université de Geneve - Coarse amenability and coarse embeddings
	The concept of coarse embedding was introduced by Gromov in 1993. It plays an important role in the study of large-scale geometry of groups and the Novikov higher signature conjecture. Guoliang Yu's property A is a weak amenability-type condition that is satisfied by many known metric spaces. It implies the existence of a coarse embedding into a Hilbert space. We construct the first example of a metric space with bounded geometry which coarsely embeds into a Hilbert space, but does not have property A. This is a joint work with Erik Guentner and Jan Spakula.