BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Ralf Meyer DTSTART:20200930T120000Z DTEND:20200930T133000Z DTSTAMP:20260404T110830Z UID:WSIPM/2 DESCRIPTION:Title: Groupoid models and C*-algebras of diagrams of groupoid correspondenc es\nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on O perator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphism between étale groupoids. Topological graphs\, self-similaritie s of groups\, or self-similar graphs are examples of this. Groupoid corre spondences induce C*-correspondences between groupoid C*-algebras\, which then give Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid correspondence is isomorphic to a groupoid C*-algebra of an étale groupo id built from the groupoid correspondence. This gives a uniform construct ion of groupoid models for many interesting C*-algebras\, such as graph C* -algebras of regular graphs\, Nekrashevych's C*-algebras of self-similar g roups and their generalisation by Exel and Pardo for self-similar graphs. If possible\, I would also like to mention work in progress to extend thi s theorem to relative Cuntz-Pimsner algebras\, which would then cover all topological graph C*-algebras.\nGroupoid correspondences form a bicategory . This structure is already used to form the groupoid model of a groupoid correspondence. It also allows us to define actions of monoids or\, more generally\, of categories on groupoids by groupoid correspondences. Pass ing to C*-algebras\, this gives a product system where the unit fibre is a groupoid C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pim sner algebra of this product system is again a groupoid C*-algebra of an étale groupoid\, which is defined directly from the action by groupoid co rrespondences. For more general monoids\, the two constructions become di fferent\, however. We show this in a special case that is related to sepa rated graph C*-algebras and their tame versions.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Aidan Sims DTSTART:20201001T103000Z DTEND:20201001T120000Z DTSTAMP:20260404T110830Z UID:WSIPM/5 DESCRIPTION:Title: Reconstruction of groupoids\, and classification of Fell algebras \nby Aidan Sims as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nI will the history of reconstruction of groupoids from pairs of operator algebras\, from Feldman and Moore’s results on v on Neumann algebras through Kumjian’s and then Renault’s results about C*-algebras of twists\, and including some recent results about groupoids that are not topologically principal. I will finish by outlining how Kumj ian’s theory leads to a Dixmier-Douady classification theorem for Fell a lgebras.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Ralf Meyer DTSTART:20201001T120000Z DTEND:20201001T133000Z DTSTAMP:20260404T110830Z UID:WSIPM/6 DESCRIPTION:Title: Groupoid models and C*-algebras of diagrams of groupoid correspondenc es\nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on O perator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphism between étale groupoids. Topological graphs\, self-similaritie s of groups\, or self-similar graphs are examples of this. Groupoid corre spondences induce C*-correspondences between groupoid C*-algebras\, which then give Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid correspondence is isomorphic to a groupoid C*-algebra of an étale groupo id built from the groupoid correspondence. This gives a uniform construct ion of groupoid models for many interesting C*-algebras\, such as graph C* -algebras of regular graphs\, Nekrashevych's C*-algebras of self-similar g roups and their generalisation by Exel and Pardo for self-similar graphs. If possible\, I would also like to mention work in progress to extend thi s theorem to relative Cuntz-Pimsner algebras\, which would then cover all topological graph C*-algebras.\nGroupoid correspondences form a bicategory . This structure is already used to form the groupoid model of a groupoid correspondence. It also allows us to define actions of monoids or\, more generally\, of categories on groupoids by groupoid correspondences. Pass ing to C*-algebras\, this gives a product system where the unit fibre is a groupoid C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pim sner algebra of this product system is again a groupoid C*-algebra of an étale groupoid\, which is defined directly from the action by groupoid co rrespondences. For more general monoids\, the two constructions become di fferent\, however. We show this in a special case that is related to sepa rated graph C*-algebras and their tame versions.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Dana Williams DTSTART:20201001T133000Z DTEND:20201001T150000Z DTSTAMP:20260404T110830Z UID:WSIPM/7 DESCRIPTION:Title: Morita equivalence\, the equivariant Brauer group\, and beyond\nb y Dana Williams as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nI will give a brief survey of work on the equivar iant Brauer group together with the necessary preliminaries as well as gen eralizations involving groupoid C*-algebras.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Gabor Szabo DTSTART:20201001T150000Z DTEND:20201001T163000Z DTSTAMP:20260404T110830Z UID:WSIPM/8 DESCRIPTION:Title: Dynamical criteria towards classifiable transformation group C*-algeb ras\nby Gabor Szabo as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nIn this talk I will report on joint work with David Kerr regarding the structure and classification of certain tran sformation group C*-algebras. It is a general important question when free minimal actions of amenable groups on compact spaces give rise to crossed product C*-algebras that fall within the scope of Elliott's program. Afte r some years of research where this had been partially settled for special classes of groups with methods related to noncommutative dimension theory \, Kerr's notion of almost finiteness opens the door to systematically stu dy this problem for all amenable groups. I will give an overview of these techniques and the current state-of-the-art\, culminating in our result th at asserts the classifiability of such crossed products if the underlying space is finite-dimensional and the group has subexponential growth.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Ralf Meyer DTSTART:20201002T103000Z DTEND:20201002T120000Z DTSTAMP:20260404T110830Z UID:WSIPM/9 DESCRIPTION:Title: Groupoid models and C*-algebras of diagrams of groupoid correspondenc es\nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on O perator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphism between étale groupoids. Topological graphs\, self-similaritie s of groups\, or self-similar graphs are examples of this. Groupoid corre spondences induce C*-correspondences between groupoid C*-algebras\, which then give Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid correspondence is isomorphic to a groupoid C*-algebra of an étale groupo id built from the groupoid correspondence. This gives a uniform construct ion of groupoid models for many interesting C*-algebras\, such as graph C* -algebras of regular graphs\, Nekrashevych's C*-algebras of self-similar g roups and their generalisation by Exel and Pardo for self-similar graphs. If possible\, I would also like to mention work in progress to extend thi s theorem to relative Cuntz-Pimsner algebras\, which would then cover all topological graph C*-algebras.\nGroupoid correspondences form a bicategory . This structure is already used to form the groupoid model of a groupoid correspondence. It also allows us to define actions of monoids or\, more generally\, of categories on groupoids by groupoid correspondences. Pass ing to C*-algebras\, this gives a product system where the unit fibre is a groupoid C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pim sner algebra of this product system is again a groupoid C*-algebra of an étale groupoid\, which is defined directly from the action by groupoid co rrespondences. For more general monoids\, the two constructions become di fferent\, however. We show this in a special case that is related to sepa rated graph C*-algebras and their tame versions.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Alcides Buss DTSTART:20201002T120000Z DTEND:20201002T133000Z DTSTAMP:20260404T110830Z UID:WSIPM/10 DESCRIPTION:Title: Amenability for actions of groups on C*-algebras\nby Alcides Bus s as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\ nAbstract\nIn this lecture I will explain recent developments in the theor y of amenability for actions of groups on C*-algebras and Fell bundles\, b ased on joint works with Siegfried Echterhoff\, Rufus Willett\, Fernando A badie and Damián Ferraro. Our main results prove that essentially all kno wn notions of amenability are equivalent. We also extend Matsumura’s the orem to actions of exact locally compact groups on commutative C*-algebras and give a counter-example for the weak containment problem for actions o n noncommutative C*-algebras.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/10/ END:VEVENT BEGIN:VEVENT SUMMARY:N. Christopher Phillips DTSTART:20201002T133000Z DTEND:20201002T150000Z DTSTAMP:20260404T110830Z UID:WSIPM/11 DESCRIPTION:Title: Crossed products by automorphisms of C(X\,D)\nby N. Christopher Phillips as part of Western Sydney\, IPM joint workshop on Operator Algebr as\n\n\nAbstract\nWe consider crossed products of\nthe form $C^* \\bigl( { \\mathbb{Z}}\, \\\, C (X\, D)\, \\\, \\alpha \\bigr)$\nin which $D$ is sim ple\, $X$ is compact metrizable\,\n$\\alpha$ induces a minimal homeomorphi sm $h \\colon X \\to X$\,\nand a mild technical assumption holds.\nIn a nu mber of examples inaccessible\nvia methods based on finite Rokhlin dimensi on\,\neither because $D$ is not ${\\mathcal{Z}}$-stable\nor because $X$ is infinite dimensional\,\nwe prove structural properties of the crossed pro duct\,\nsuch as (tracial) ${\\mathcal{Z}}$-stability\, stable rank one\,\n real rank zero\, and pure infiniteness.\n\nThe method is to find a central ly large subalgebra\nof the crossed product which is a direct limit of\n`` recursive subhomogeneous algebras over $D$''.\nWith a better understanding of such direct limits\,\nmany more examples would become accessible.\n\nT his is joint work with Dawn Archey and Julian Buck.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Alex Kumjian DTSTART:20201002T150000Z DTEND:20201002T163000Z DTSTAMP:20260404T110830Z UID:WSIPM/12 DESCRIPTION:Title: Pushouts of groupoid extensions by abelian group bundles\nby Ale x Kumjian as part of Western Sydney\, IPM joint workshop on Operator Algeb ras\n\n\nAbstract\nGiven a groupoid extension of a locally compact Hausdor ff groupoid by a bundle of abelian groups on which it acts\, we construct a pushout twist over the groupoid semidirect product of the groupoid actin g on the dual of the bundle regarded as a topological space. We then sho w that the C*-algebra of the original extension groupoid is isomorphic to the twisted groupoid associated to the pushout. We will also discuss exam ples. This talk is based on current joint work with Marius Ionescu\, Jean Renault\, Aidan Sims and Dana Williams.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Aidan Sims DTSTART:20200930T103000Z DTEND:20200930T120000Z DTSTAMP:20260404T110830Z UID:WSIPM/24 DESCRIPTION:Title: Reconstruction of groupoids\, and classification of Fell algebras\nby Aidan Sims as part of Western Sydney\, IPM joint workshop on Operato r Algebras\n\n\nAbstract\nI will the history of reconstruction of groupoid s from pairs of operator algebras\, from Feldman and Moore’s results on von Neumann algebras through Kumjian’s and then Renault’s results abou t C*-algebras of twists\, and including some recent results about groupoid s that are not topologically principal. I will finish by outlining how Kum jian’s theory leads to a Dixmier-Douady classification theorem for Fell algebras.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Dana Williams DTSTART:20200930T133000Z DTEND:20200930T150000Z DTSTAMP:20260404T110830Z UID:WSIPM/26 DESCRIPTION:Title: Morita equivalence\, the equivariant Brauer group\, and beyond\n by Dana Williams as part of Western Sydney\, IPM joint workshop on Operato r Algebras\n\n\nAbstract\nI will give a brief survey of work on the equiva riant Brauer group together with the necessary preliminaries as well as ge neralizations involving groupoid C*-algebras.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Jean Renault DTSTART:20200930T150000Z DTEND:20200930T163000Z DTSTAMP:20260404T110830Z UID:WSIPM/27 DESCRIPTION:Title: KMS states and groupoid C*-algebras\nby Jean Renault as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nI will illustrate the use of groupoids in the study of KMS states and weight s on C*-algebras. The KMS condition\, which was introduced in quantum stat istical mechanics to characterize equilibrium states\, plays a crucial rol e in the theory of von Neumann algebras. The study of KMS states and their phase transitions on specific C*-algebras\, in particular graph algebras\ , is an active field of research where the groupoid techniques are well su ited.\n LOCATION:https://stable.researchseminars.org/talk/WSIPM/27/ END:VEVENT END:VCALENDAR