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Operator Algebra Seminars
Seminar information archive ～11/02｜Next seminar｜Future seminars 11/03～
| Date, time & place | Monday 15:30 - 17:00 Room # (Graduate School of Math. Sci. Bldg.) |
|---|---|
| Organizer(s) | MATUI Hiroki, KIDA Yoshikata, KAWAHIGASHI Yasuyuki |
Future seminars
2026/11/09
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Hikaru Sekiyama (Keio University)
KS-Groupoids and KS-Crossed Products associated with Inverse Semigroup Actions
Hikaru Sekiyama (Keio University)
KS-Groupoids and KS-Crossed Products associated with Inverse Semigroup Actions
2026/11/16
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Kohki Sakamoto (The University of Tokyo)
Continuity results for random walks in hyperbolic percolation
Kohki Sakamoto (The University of Tokyo)
Continuity results for random walks in hyperbolic percolation
[ Abstract ]
Benjamini, Lyons, and Schramm proved that the simple random walk on the infinite cluster of supercritical Bernoulli percolation exhibits positive drift and entropy, provided the underlying graph is the Cayley graph of a non-amenable group. A natural question then arises: how do these asymptotic quantities vary with the percolation parameter? In this talk, I will provide some background on this topic and show that these quantities are continuous in the parameter when the group is Gromov hyperbolic. I will also discuss how this continuity contrasts with the conjectured behavior of
the Hausdorff dimension of the limit set.
Benjamini, Lyons, and Schramm proved that the simple random walk on the infinite cluster of supercritical Bernoulli percolation exhibits positive drift and entropy, provided the underlying graph is the Cayley graph of a non-amenable group. A natural question then arises: how do these asymptotic quantities vary with the percolation parameter? In this talk, I will provide some background on this topic and show that these quantities are continuous in the parameter when the group is Gromov hyperbolic. I will also discuss how this continuity contrasts with the conjectured behavior of
the Hausdorff dimension of the limit set.
2026/11/30
15:30-17:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Fuyuta Komura (Kyushu Institute of Technology)
Cartan-preserving *-automorphism groups: realization and obstructions for compact abelian groups
Fuyuta Komura (Kyushu Institute of Technology)
Cartan-preserving *-automorphism groups: realization and obstructions for compact abelian groups
[ Abstract ]
In this talk, we investigate automorphism groups preserving Cartan subalgebras of C*-algebras. First, we describe these groups in terms of automorphisms and 1-cocycles of twisted étale groupoids. As a consequence, we obtain a C*-algebraic analogue of a theorem of Feldman and Moore on Cartan-preserving automorphisms of von Neumann algebras. We then study Cartan-fixing automorphism groups. We show that every UCT Kirchberg algebra admits a Cartan subalgebra whose Cartan-fixing automorphism group contains every second countable compact abelian group. In contrast, for C*-algebras arising from expansive effective groupoids, we prove that compact Cartan-fixing automorphism groups must have finitely generated Pontryagin duals if the fixed point subalgebras are prime. As an application, we establish the existence of inequivalent Cartan subalgebras for Kirchberg algebras arising from expansive effective groupoids.
In this talk, we investigate automorphism groups preserving Cartan subalgebras of C*-algebras. First, we describe these groups in terms of automorphisms and 1-cocycles of twisted étale groupoids. As a consequence, we obtain a C*-algebraic analogue of a theorem of Feldman and Moore on Cartan-preserving automorphisms of von Neumann algebras. We then study Cartan-fixing automorphism groups. We show that every UCT Kirchberg algebra admits a Cartan subalgebra whose Cartan-fixing automorphism group contains every second countable compact abelian group. In contrast, for C*-algebras arising from expansive effective groupoids, we prove that compact Cartan-fixing automorphism groups must have finitely generated Pontryagin duals if the fixed point subalgebras are prime. As an application, we establish the existence of inequivalent Cartan subalgebras for Kirchberg algebras arising from expansive effective groupoids.
2026/12/07
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Akihiro Miyagawa (Kyoto University)
TBA
Akihiro Miyagawa (Kyoto University)
TBA
2026/12/14
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Yuki Arano (Nagoya University)
Prime actions of compact groups on von Neumann algebras
Yuki Arano (Nagoya University)
Prime actions of compact groups on von Neumann algebras
2026/12/21
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Mutsuki Kobashikawa (The University of Tokyo)
TBA
Mutsuki Kobashikawa (The University of Tokyo)
TBA
2027/01/18
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Katsunori Fujie (Aichi Prefectural University)
TBA
Katsunori Fujie (Aichi Prefectural University)
TBA
2027/02/01
15:30-17:00 Room # 126 (Graduate School of Math. Sci. Bldg.)
Ikhan Choi (The University of Tokyo)
Analytic Kasparov product for non-separable C*-algebras
Ikhan Choi (The University of Tokyo)
Analytic Kasparov product for non-separable C*-algebras
