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:20260422T225658Z UID:WSIPM/2 DESCRIPTION:Title: Gr oupoid models and C*-algebras of diagrams of groupoid correspondences\ nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphi sm between étale groupoids. Topological graphs\, self-similarities of gr oups\, or self-similar graphs are examples of this. Groupoid corresponden ces induce C*-correspondences between groupoid C*-algebras\, which then gi ve Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid corres pondence is isomorphic to a groupoid C*-algebra of an étale groupoid buil t from the groupoid correspondence. This gives a uniform construction of groupoid models for many interesting C*-algebras\, such as graph C*-algebr as of regular graphs\, Nekrashevych's C*-algebras of self-similar groups a nd their generalisation by Exel and Pardo for self-similar graphs. If pos sible\, I would also like to mention work in progress to extend this theor em to relative Cuntz-Pimsner algebras\, which would then cover all topolog ical graph C*-algebras.\nGroupoid correspondences form a bicategory. This structure is already used to form the groupoid model of a groupoid corres pondence. It also allows us to define actions of monoids or\, more genera lly\, of categories on groupoids by groupoid correspondences. Passing to C*-algebras\, this gives a product system where the unit fibre is a groupo id C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pimsner al gebra of this product system is again a groupoid C*-algebra of an étale g roupoid\, which is defined directly from the action by groupoid correspond ences. For more general monoids\, the two constructions become different\ , however. We show this in a special case that is related to separated gr aph C*-algebras and their tame versions.\n LOCATION:https://researchseminars.org/talk/WSIPM/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Aidan Sims DTSTART:20201001T103000Z DTEND:20201001T120000Z DTSTAMP:20260422T225658Z UID:WSIPM/5 DESCRIPTION:Title: Re construction of groupoids\, and classification of Fell algebras\nby Ai dan Sims as part of Western Sydney\, IPM joint workshop on Operator Algebr as\n\n\nAbstract\nI will the history of reconstruction of groupoids from p airs of operator algebras\, from Feldman and Moore’s results on von Neum ann algebras through Kumjian’s and then Renault’s results about C*-alg ebras of twists\, and including some recent results about groupoids that a re not topologically principal. I will finish by outlining how Kumjian’s theory leads to a Dixmier-Douady classification theorem for Fell algebras .\n LOCATION:https://researchseminars.org/talk/WSIPM/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Ralf Meyer DTSTART:20201001T120000Z DTEND:20201001T133000Z DTSTAMP:20260422T225658Z UID:WSIPM/6 DESCRIPTION:Title: Gr oupoid models and C*-algebras of diagrams of groupoid correspondences\ nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphi sm between étale groupoids. Topological graphs\, self-similarities of gr oups\, or self-similar graphs are examples of this. Groupoid corresponden ces induce C*-correspondences between groupoid C*-algebras\, which then gi ve Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid corres pondence is isomorphic to a groupoid C*-algebra of an étale groupoid buil t from the groupoid correspondence. This gives a uniform construction of groupoid models for many interesting C*-algebras\, such as graph C*-algebr as of regular graphs\, Nekrashevych's C*-algebras of self-similar groups a nd their generalisation by Exel and Pardo for self-similar graphs. If pos sible\, I would also like to mention work in progress to extend this theor em to relative Cuntz-Pimsner algebras\, which would then cover all topolog ical graph C*-algebras.\nGroupoid correspondences form a bicategory. This structure is already used to form the groupoid model of a groupoid corres pondence. It also allows us to define actions of monoids or\, more genera lly\, of categories on groupoids by groupoid correspondences. Passing to C*-algebras\, this gives a product system where the unit fibre is a groupo id C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pimsner al gebra of this product system is again a groupoid C*-algebra of an étale g roupoid\, which is defined directly from the action by groupoid correspond ences. For more general monoids\, the two constructions become different\ , however. We show this in a special case that is related to separated gr aph C*-algebras and their tame versions.\n LOCATION:https://researchseminars.org/talk/WSIPM/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Dana Williams DTSTART:20201001T133000Z DTEND:20201001T150000Z DTSTAMP:20260422T225658Z UID:WSIPM/7 DESCRIPTION:Title: Mo rita equivalence\, the equivariant Brauer group\, and beyond\nby Dana Williams as part of Western Sydney\, IPM joint workshop on Operator Algebr as\n\n\nAbstract\nI will give a brief survey of work on the equivariant Br auer group together with the necessary preliminaries as well as generaliza tions involving groupoid C*-algebras.\n LOCATION:https://researchseminars.org/talk/WSIPM/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Gabor Szabo DTSTART:20201001T150000Z DTEND:20201001T163000Z DTSTAMP:20260422T225658Z UID:WSIPM/8 DESCRIPTION:Title: Dy namical criteria towards classifiable transformation group C*-algebras \nby Gabor Szabo as part of Western Sydney\, IPM joint workshop on Operato r Algebras\n\n\nAbstract\nIn this talk I will report on joint work with Da vid Kerr regarding the structure and classification of certain transformat ion group C*-algebras. It is a general important question when free minima l actions of amenable groups on compact spaces give rise to crossed produc t C*-algebras that fall within the scope of Elliott's program. After some years of research where this had been partially settled for special classe s of groups with methods related to noncommutative dimension theory\, Kerr 's notion of almost finiteness opens the door to systematically study this problem for all amenable groups. I will give an overview of these techniq ues and the current state-of-the-art\, culminating in our result that asse rts the classifiability of such crossed products if the underlying space i s finite-dimensional and the group has subexponential growth.\n LOCATION:https://researchseminars.org/talk/WSIPM/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Ralf Meyer DTSTART:20201002T103000Z DTEND:20201002T120000Z DTSTAMP:20260422T225658Z UID:WSIPM/9 DESCRIPTION:Title: Gr oupoid models and C*-algebras of diagrams of groupoid correspondences\ nby Ralf Meyer as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nA groupoid correspondence is a generalised morphi sm between étale groupoids. Topological graphs\, self-similarities of gr oups\, or self-similar graphs are examples of this. Groupoid corresponden ces induce C*-correspondences between groupoid C*-algebras\, which then gi ve Cuntz-Pimsner algebras. The Cuntz-Pimsner algebra of a groupoid corres pondence is isomorphic to a groupoid C*-algebra of an étale groupoid buil t from the groupoid correspondence. This gives a uniform construction of groupoid models for many interesting C*-algebras\, such as graph C*-algebr as of regular graphs\, Nekrashevych's C*-algebras of self-similar groups a nd their generalisation by Exel and Pardo for self-similar graphs. If pos sible\, I would also like to mention work in progress to extend this theor em to relative Cuntz-Pimsner algebras\, which would then cover all topolog ical graph C*-algebras.\nGroupoid correspondences form a bicategory. This structure is already used to form the groupoid model of a groupoid corres pondence. It also allows us to define actions of monoids or\, more genera lly\, of categories on groupoids by groupoid correspondences. Passing to C*-algebras\, this gives a product system where the unit fibre is a groupo id C*-algebra. If the monoid is an Ore monoid\, then the Cuntz-Pimsner al gebra of this product system is again a groupoid C*-algebra of an étale g roupoid\, which is defined directly from the action by groupoid correspond ences. For more general monoids\, the two constructions become different\ , however. We show this in a special case that is related to separated gr aph C*-algebras and their tame versions.\n LOCATION:https://researchseminars.org/talk/WSIPM/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Alcides Buss DTSTART:20201002T120000Z DTEND:20201002T133000Z DTSTAMP:20260422T225658Z UID:WSIPM/10 DESCRIPTION:Title: A menability for actions of groups on C*-algebras\nby Alcides Buss as pa rt of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstra ct\nIn this lecture I will explain recent developments in the theory of am enability for actions of groups on C*-algebras and Fell bundles\, based on joint works with Siegfried Echterhoff\, Rufus Willett\, Fernando Abadie a nd Damián Ferraro. Our main results prove that essentially all known noti ons of amenability are equivalent. We also extend Matsumura’s theorem to actions of exact locally compact groups on commutative C*-algebras and gi ve a counter-example for the weak containment problem for actions on nonco mmutative C*-algebras.\n LOCATION:https://researchseminars.org/talk/WSIPM/10/ END:VEVENT BEGIN:VEVENT SUMMARY:N. Christopher Phillips DTSTART:20201002T133000Z DTEND:20201002T150000Z DTSTAMP:20260422T225658Z UID:WSIPM/11 DESCRIPTION:Title: C rossed products by automorphisms of C(X\,D)\nby N. Christopher Phillip s as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\ nAbstract\nWe consider crossed products of\nthe form $C^* \\bigl( {\\mathb b{Z}}\, \\\, C (X\, D)\, \\\, \\alpha \\bigr)$\nin which $D$ is simple\, $ X$ is compact metrizable\,\n$\\alpha$ induces a minimal homeomorphism $h \ \colon X \\to X$\,\nand a mild technical assumption holds.\nIn a number of examples inaccessible\nvia methods based on finite Rokhlin dimension\,\ne ither because $D$ is not ${\\mathcal{Z}}$-stable\nor because $X$ is infini te dimensional\,\nwe prove structural properties of the crossed product\,\ nsuch as (tracial) ${\\mathcal{Z}}$-stability\, stable rank one\,\nreal ra nk zero\, and pure infiniteness.\n\nThe method is to find a centrally larg e subalgebra\nof the crossed product which is a direct limit of\n``recursi ve subhomogeneous algebras over $D$''.\nWith a better understanding of suc h direct limits\,\nmany more examples would become accessible.\n\nThis is joint work with Dawn Archey and Julian Buck.\n LOCATION:https://researchseminars.org/talk/WSIPM/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Alex Kumjian DTSTART:20201002T150000Z DTEND:20201002T163000Z DTSTAMP:20260422T225658Z UID:WSIPM/12 DESCRIPTION:Title: P ushouts of groupoid extensions by abelian group bundles\nby Alex Kumji an as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n \nAbstract\nGiven a groupoid extension of a locally compact Hausdorff grou poid by a bundle of abelian groups on which it acts\, we construct a pusho ut twist over the groupoid semidirect product of the groupoid acting on th e dual of the bundle regarded as a topological space. We then show that the C*-algebra of the original extension groupoid is isomorphic to the twi sted groupoid associated to the pushout. We will also discuss examples. This talk is based on current joint work with Marius Ionescu\, Jean Renaul t\, Aidan Sims and Dana Williams.\n LOCATION:https://researchseminars.org/talk/WSIPM/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Aidan Sims DTSTART:20200930T103000Z DTEND:20200930T120000Z DTSTAMP:20260422T225658Z UID:WSIPM/24 DESCRIPTION:Title: R econstruction of groupoids\, and classification of Fell algebras\nby A idan Sims as part of Western Sydney\, IPM joint workshop on Operator Algeb ras\n\n\nAbstract\nI will the history of reconstruction of groupoids from pairs of operator algebras\, from Feldman and Moore’s results on von Neu mann algebras through Kumjian’s and then Renault’s results about C*-al gebras of twists\, and including some recent results about groupoids that are not topologically principal. I will finish by outlining how Kumjian’ s theory leads to a Dixmier-Douady classification theorem for Fell algebra s.\n LOCATION:https://researchseminars.org/talk/WSIPM/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Dana Williams DTSTART:20200930T133000Z DTEND:20200930T150000Z DTSTAMP:20260422T225658Z UID:WSIPM/26 DESCRIPTION:Title: M orita equivalence\, the equivariant Brauer group\, and beyond\nby Dana Williams as part of Western Sydney\, IPM joint workshop on Operator Algeb ras\n\n\nAbstract\nI will give a brief survey of work on the equivariant B rauer group together with the necessary preliminaries as well as generaliz ations involving groupoid C*-algebras.\n LOCATION:https://researchseminars.org/talk/WSIPM/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Jean Renault DTSTART:20200930T150000Z DTEND:20200930T163000Z DTSTAMP:20260422T225658Z UID:WSIPM/27 DESCRIPTION:Title: K MS states and groupoid C*-algebras\nby Jean Renault as part of Western Sydney\, IPM joint workshop on Operator Algebras\n\n\nAbstract\nI will il lustrate the use of groupoids in the study of KMS states and weights on C* -algebras. The KMS condition\, which was introduced in quantum statistical mechanics to characterize equilibrium states\, plays a crucial role in th e 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 suited.\n LOCATION:https://researchseminars.org/talk/WSIPM/27/ END:VEVENT END:VCALENDAR