Events - Page 7

Time and place: Nov. 28, 2012 2:15 PM4:00 PM, NHA, seminarrom B71

Jyotishman Bhowmick, UiO, will give a talk with title: Deformation of operator algebras by Borel cocycles

 

Abstract:Given a coaction of a locally compact group on a C^* algebra and fixing a cocycle on G, we discuss a method to deform A into another C^* algebra, thus generalizing  the works of Kasprzak, Yamashita and Rieffel. This is a joint work with S. Neshveyev and A.S. Sangha.

Time and place: Nov. 21, 2012 2:15 PM4:00 PM, NHA, seminarrom B71

Stuart White (University of Glasgow, UK) will talk on "Z-stability and central sequences".

Abstract: Over recent years, tensorial absorption of the Jiang-Su algebra $\mathcal Z$ has become a particularly prominent property of $C^*$-algebras. In this talk, I'll explain what this means, and why this is the case; I'll also discuss methods for establishing ``$\mathcal Z$''-stability using central sequence, and some more general properties of central sequence algebras. The talk will end with a recent result showing that for a simple separable unital nuclear C*-algebra, whose extremal traces are compact and of finite covering dimension $\mathcal Z$-stability can be detected by a comparison property of the Cuntz semigroup (this result is joint work with Andrew Toms and Wilhelm Winter, which has also been independently discovered by Eberhard Kirchberg and Mickael Rørdam, and by Yasuhiko Sato).  

Time and place: Nov. 12, 2012 10:15 AM12:00 PM, NHA, seminarrom B62

Dana Williams, Dartmouth College (USA) will talk on "Equivalence theorems and linking groupoids".

 

 

Time and place: Oct. 24, 2012 1:15 PM3:00 PM, NHA, seminarrom B62
Time and place: Sep. 19, 2012 2:15 PM4:00 PM, NHA, seminarrom B71

 

Abstract: The Kolmogorov decomposition of positive scalar valued kernels has played an important role in applications of operator theory to function theory.  It has been vastly generalised, finding its apotheosis in the result of Baretto, Bhat, Liebscher and Skeide which states that a positive $L(A,B)$-valued kernel, $A$ and $B$ $C^*$-algebras, has a Kolmogorov decomposition if and only if it is completely positive; that is, the restriction of the kernel to any finite set of index points gives a completely positive map.  The result may be viewed as a generalisation of the Stinespring dilation theorem from single point to multi-point index sets.  This talk presents the analogue of the Haagerup-Paulsen-Wittstock decomposition theorem for $L(A,B)$-valued kernels (where now $B$ is assumed to be injective).  It happens that in general complete boundedness of the kernel (ie, complete boundedness of the map resulting from restriction of the kernel to any finite index set) is not quite enough to ensure a decomposition: a certain regularity condition must also hold.  This condition can be seen to be automatic if the kernel is completely positive or the index set is countable.  This is joint work with Tirthankar Bhattacharyya and Chris Todd.  

Time and place: Aug. 22, 2012 2:15 PM3:15 PM, NHA, seminarrom B71

Dávid Kunszenti-Kovács, Tübingen University (Germany) will give a talk with title "The Jacobs-deLeeuw-Glicksberg decomposition and ergodic theorems".

Abstract: We present the classical decomposition theorem for contractions on Hilbert spaces due to Jacobs, deLeeuw and Glicksberg, and show how it can be used to prove ergodic theorems. We then prove a new version of this decomposition, adapted to the context of W*-algebras, with consequences for W*-dynamical systems. Finally we take a look at how the characterizations given in the original decomposition theorem can be further strengthened.  

Time and place: Aug. 16, 2012 2:15 PM4:00 PM, NHA, seminarrom B71

John Quigg, University of Arizona (Tempe), USA, will give a talk with title "Exotic group C*-algebras"

Abstract: We study C*-algebras between C*(G) and C*_r(G), focusing on the aspects relevant to noncommutative crossed-product duality.  

Time and place: Apr. 19, 2012 12:30 PM, seminarrom B71

Erik Alfsen will give a talk with title  "Finding decompositions of separable states"

 

Time and place: Mar. 15, 2012 12:30 PM2:00 PM, NHA, seminarrom B71

Magnus Dahler Norling will give a second talk on the topic of inverse semigroup C*-algebras associated with left cancellative semigroups.

Time and place: Mar. 8, 2012 12:30 PM2:00 PM, NHA, seminarrom B71

Magnus Dahler Norling will give a talk with title "Inverse semigroup C*-algebras associated with left cancellative semigroups".

 

Abstract: To each discrete left cancellative semigroup S one may associate a certain inverse semigroup I_l(S), often called the left inverse hull of S. We show how the full and the reduced C*-algebras of I_l(S) are related to the full and the reduced semigroup C*-algebras for S recently introduced by Xin Li, and give conditions ensuring that these algebras are isomorphic. Our picture provides an enhanced understanding of Li's algebras.  

Time and place: Mar. 1, 2012 12:30 PM2:00 PM, NHA, seminarrom B71

Simen Rustad (UiO) will give a talk with title  "Construction of Bost-Connes type systems for function fields".

 

Abstract: I will try to indicate how Benoit Jacob's construction of a Bost-Connes  type system for function fields fits into a more general framework.  

Time and place: Feb. 23, 2012 12:30 PM2:00 PM, NHA, seminarrom B71

Bora Yalkinoglu will give a talk entitled: Introduction to p-adic Bost-Connes systems.

Abstract: In this talk we want to give a gentle introduction into the recently emerging theory of p-adic Bost-Connes systems. In the first part of the talk, after reviewing the necessary background from p-adic analysis and number theory, we will explain recent work of Connes and Consani on certain p-adic representations of the classical BC-system. In the second part of the talk we will discuss recent work on generalizations of the work of Connes and Consani and, further, point out several open problems for further research.  

Time and place: Feb. 13, 2012 2:15 PM4:00 PM, NHA, seminarrom B71

Thomas Timmermann, Westfälische Wilhelms-Universität Münster, Germany, will give a talk with title "Towards the dynamical quantum group SU_q(2) on the level of operator algebras"

Time and place: Jan. 26, 2012 12:30 PM2:00 PM, NHA, seminarrom B71

Fred Shultz, Wellesley College (USA) will give a talk with title "Affine automorphisms of the convex set of separable states, and decompositions of separable states".

Time and place: Nov. 24, 2011 12:15 PM2:00 PM, B62, NHA hus

Roberto Conti , Università di Chieti-Pescara ‘G. D’Annunzio’, Italy, will give a talk on "Sectors of scaling limit nets and asymptotic morphisms".

 

Abstract: In the algebraic approach to 4D-QFT the main object of study is a local net, namely an isotonous correspondence between spacetime regions and operator algebras on a fixed Hilbert space satisfying physically motivated properties including Einstein causality. The so-called DHR superselection sectors of the net are then described by certain (inner equivalence classes of) *-endomorphisms of the C*-algebra of quasi-local observables. For any local net, one may also consider its associated scaling limit nets, carrying the information on the short distance limit of the given QFT (roughly, this is the algebraic version of the renormalization group). In this talk we will argue that the superselection sectors of a scaling limit net can be described in terms of suitable maps of the original theory, that are similar to the asymptotic morphisms appearing in E-theory of Connes and Higson. This is a new arena where concepts from AQFT and NCG are merged together, and provides a first step for an alternative (rigorous, model independent) approach to the notion of confinement. (This is joint work with G. Morsella).  

Time and place: Nov. 18, 2011 12:30 PM2:00 PM, B70, NHA Hus
Time and place: Nov. 11, 2011 12:30 PM2:00 PM, NHA, seminarrom B71