George A. Elliott, Department of Mathematics, University of Toronto, Toronto, Canada M5S 2E4; e-mail: elliott@math.toronto.edu

Abstract/Résumé:

It is shown that for a unital C*-algebra, what is sometimes referred to as the Elliott invariant—loosely speaking, K-theory and traces— i.e., the order-unit K\(_0\)-group, the K\(_1\)-group, and the trace simplex, paired in the natural way with K\(_0\), can be expressed purely in terms of K-theory, with the trace simplex and its pairing with K\(_0\) recoverable in a simple way (using polar decomposition) from algebraic K\(_1\), defined as in the purely algebraic context using invertible elements rather than just unitaries.

L’invariant naïf d’Elliott, qui est à la base de la classification complète récente d’une énorme classe de C*-algèbres simples (celles qui sont de dimension nucléaire finie, qui sont séparables, et qui satisfont à l’UCT), peut s’exprimer entièrement dans le cadre de K-théorie algébrique.

Keywords: Algebraic K1-group of a C*-algebra encodes bounded traces

AMS Subject Classification: None of the above; but in this section, $K_0$ as an ordered group; traces, General theory of $C^*$-algebras, Classifications of $C^*$-algebras; factors, K-theory and operator algebras -including cyclic theory 19B99, 19K14, 46L05, 46L35, 46L80

PDF(click to download): K-Theory and Traces

Bit Na Choi, Department of Mathematics and Statistics, University of New Hampshire, Durham, NH 03824, USA; e-mail: Bitna.Choi@unh.edu

Andrew J. Dean, Department of Mathematical Sciences, Lakehead University, Thunder Bay, ON, Canada P7B 5E1; e-mail: ajdean@lakeheadu.ca

Abstract/Résumé:

We show that a \(\mathbb{Z}_2\) action on a lattice-ordered dimension group will arise as an inductive limit of \(\mathbb{Z}_2\) actions on simplicial groups. The motivation for this study is the range of invariant problem in Elliott and Su’s classification of AF type \(\mathbb{Z}_2\) actions. We modify the proof of the Effros-Handelman-Shen theorem to include \(\mathbb{Z}_2\) actions.

Nous montrons qu’une action de \(\mathbb{Z}_2\) sur un groupe de dimension ordonné par treillis apparaît comme une limite inductive d’actions de \(\mathbb{Z}_2\) sur des groupes simpliciaux. La motivation de cette étude est le problème de la gamme de l’invariant dans la classification d’Elliott et de Su des actions de \(\mathbb{Z}_2\) de type AF. Nous modifions la preuve du théorème d’Effros-Handelman-Shen pour inclure les actions de \(\mathbb{Z}_2\).

Keywords: Dimension groups, K-theory, classification

AMS Subject Classification: Ordered abelian groups; Riesz groups; ordered linear spaces, $K_0$ as an ordered group; traces 06F20, 19K14

PDF(click to download): A Modification of the Effros-Handelman-Shen Theorem with ${Z}_2$ actions

Gregory R. Maloney, Department of Mathematics, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125-3393, USA; e-mail: gmaloney@math.umb.edu

Abstract/Résumé:

We describe a class of dimension groups associated with multidimensional continued fractions and show how a certain property of a continued fraction is reflected in the structure of its dimension group.

On décrit une classe de groupes de dimensions associés aux fractions continues multidimensionnelles et on montre comment une certaine propriété d’une fraction continue se reflète dans la structure de son groupe de dimensions.

Keywords:

AMS Subject Classification: $K_0$ as an ordered group; traces 19K14

PDF(click to download): Dimension groups and multidimensional continued fractions

S.G. Walters

Abstract/Résumé:

No abstract available but the full text pdf may be downloaded at the title link below.

Keywords: C*-algebra, Chern characters, K-theory, automorphisms, rotation algebras, unbounded traces

AMS Subject Classification: $K_0$ as an ordered group; traces, Automorphisms, K-theory and operator algebras -including cyclic theory 19K14, 46L40, 46L80

PDF(click to download): On the irrational quartic algebra