# Kalender – Københavns Universitet

Institut for Matematiske Fag > Kalender

# Begivenheder onsdag den 6. juni 2012

Baby NCG Seminar
CAPoW!
Taler(e): Søren Knudby, Tim de Laat
Onsdag den 6. juni 2012 kl. 13:15-14:00. Sted: Aud 7. Sprog: engelsk.

Søren will be presenting the following preprint:
arXiv:1205.4649 New C*-completions of discrete groups and related spaces
Authors: Nathanial P. Brown, Erik Guentner

Abstract: Let $\Gamma$ be a discrete group. To every ideal in $\ell^{\infty}(\G)$ we associate a C$^*$-algebra completion of the group ring that encapsulates the unitary representations with matrix coefficients belonging to the ideal. The general framework we develop unifies some classical results and leads to new insights. For example, we give the first C$^*$-algebraic characterization of a-T-menability; a new characterization of property (T); new examples of "exotic" quantum groups; and, after extending our construction to transformation groupoids, we improve
and simplify a recent result of Douglas and Nowak.

Tim will be presenting the following preprint:
arXiv:1205.2862 Groups associated to $II_1$-factors
Authors: Nathanial P. Brown, Valerio Capraro

Abstract: We extend recent work of the first named author, constructing a natural Hom semigroup associated to any pair of II$_1$-factors. This semigroup always satisfies cancelation, hence embeds into its Grothendieck group. When the target is an ultraproduct of a McDuff factor (e.g., $R^\omega$), this Grothendieck group turns out to carry a natural vector space structure; in fact, it is a Banach space with natural actions of outer automorphism groups.

Organiseret af Tim and Jamie

Operatoralgebraseminar
A complete classification of unital graph C*-algebras?
Taler(e): Søren Eilers
(University of Copenhagen)
Onsdag den 6. juni 2012 kl. 15:15-16:15. Sted: Aud 8. Sprog: engelsk.

I will discuss recent advances on the problem on classifying unital graph C*-algebras up to stable or exact isomorphism. The question mark in the title indicates that there are still a number technical items that need scrutiny, but if indeed this is a theorem, it is joint with Ruiz and Sørensen.

Organiseret af SE