Updated on 2024/12/01

Information

 

写真a

 
SATO YASUHIKO
 
Organization
Faculty of Mathematics Division of Analysis Associate Professor
School of Sciences Department of Mathematics(Concurrent)
Graduate School of Mathematics Department of Mathematics(Concurrent)
Joint Graduate School of Mathematics for Innovation (Concurrent)
Title
Associate Professor
Homepage
External link

Research Interests・Research Keywords

  • Research theme: The main theme of my research is the theory of operator algebras and their group actions. Although operator algebras are basically represented on infinite dimensional linear spaces, it is important to consider approximations by finite dimensional spaces in several topologies. Often times, an elementary technique of finite dimensional matrices plays a key role. The main goal of my research is to characterize classifiable C*-algebras abstractly. In particular, I am interested in the following problems. 1. Amenable C*-algebras, nuclear dimension, and Toms-Winter conjecture, 2. The classification theory of group actions on the Jiang-Su algebra, 3. Quasidiagonality, Rosenberg conjecture, and Blackadar-Kirchberg conjecture.

    Keyword: Operator Algebras, C*-algebras, Group Actions, Nuclear Dimension, Classification Theory

    Research period: 2020.4 - 2023.4

Awards

  • 作用素環賞

    2020.11   作用素環後援会  

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    https://www.mathsoc.jp/assets/file/publications/tushin/2504/6-OperatorRing.pdf

  • 建部賢弘賞奨励賞

    2012.9   日本数学会  

Papers

  • Rationally AF algebras and KMS states of Z-absorbing C*-algebras Invited International journal

    G.A.Elliott, Y. Sato

    arXiv:2207.11653   2022.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    Repository Public URL: https://hdl.handle.net/2324/7173589

  • On the Bundle of KMS State Spaces for Flows on a Z-Absorbing C*-Algebra Reviewed International journal

    #佐藤 康彦, @G.E.Elliott, @K. Thomsen

    Communications in Mathematical Physics (2022)   2022.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

  • Endomorphisms of Z-absorbing C*-algebras without conditional expectations Reviewed International journal

    Yasuhiko Sato

    Munster Journal of Mathematics   2023.9

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    Language:English   Publishing type:Research paper (scientific journal)  

  • On the bundle of KMS state spaces for flows on a Z-absorbing C*-algebra International journal

    Yasuhiko Sato, G. E. Elliott, K. Thomsen

    https://arxiv.org/search/?query=Thomsen+Sato&searchtype=all   2021.12

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    We obtain three results: 1) Every compact simplex bundle with exactly one point in the fiber over 0 is the KMS bundle of a periodic flow on the Jiang-Su algebra. 2) Let A be a separable unital C*-algebra with a unique trace state. Suppose that A tensorially absorbs the Jiang-Su algebra. The (weak) cocycle-conjugacy classes of flows that are not approximately inner are uncountable. 3) Let B be a separable, simple, unital, purely infinite and nuclear C*-algebra in the UCT class. Assume that the K1 group of B is torsion free. Every proper simplex bundle with empty fiber over 0 is the KMS bundle of a periodic flow on B.

  • 2-positive almost order zero maps and decomposition rank Reviewed International journal

    Yasuhiko Sato

    Journal of Operator Theory   2020.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    We consider 2-positive almost order zero (disjointness preserving) maps on C*-algebras. Generalizing the argument of M. Choi for multiplicative domains, we give an internal characterization of almost order zero for 2-positive maps. It is also shown that complete positivity can be reduced to 2-positivity in the definition of decomposition rank for unital separable C*-algebras.

  • Covering dimension of C∗-algebras and 2-coloured classification Reviewed

    Joan Bosa, Nathanial P. Brown, Yasuhiko Sato, Aaron Tikuisis, Stuart White, Wilhelm Winter

    Memoirs of the American Mathematical Society   257 ( 1233 )   1 - 112   2019.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    We introduce the concept of finitely coloured equivalence for unital ∗-homomorphisms between C∗-algebras, for which unitary equivalence is the 1- coloured case. We use this notion to classify ∗-homomorphisms from separable, unital, nuclear C∗-algebras into ultrapowers of simple, unital, nuclear, Z-stable C∗- algebras with compact extremal trace space up to 2-coloured equivalence by their behaviour on traces; this is based on a 1-coloured classification theorem for certain order zero maps, also in terms of tracial data. As an application we calculate the nuclear dimension of non-AF, simple, separable, unital, nuclear, Z-stable C∗-algebras with compact extremal trace space: it is 1. In the case that the extremal trace space also has finite topological covering dimension, this confirms the remaining open implication of the Toms-Winter conjecture. Inspired by homotopy-rigidity theorems in geometry and topology, we derive a "homotopy equivalence implies isomorphism" result for large classes of C∗-algebras with finite nuclear dimension.

    DOI: 10.10.1090/memo/1233

  • Actions of amenable groups and crossed products of Z-absorbing C*-algebras Reviewed

    Yasuhiko Sato

    Advanced Studies in Pure mathematics   80 ( 5 )   189 - 210   2019

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    Language:English   Publishing type:Research paper (scientific journal)  

  • C*環の分類理論の進展 Reviewed

    佐藤 康彦

    数学   70 ( 1 )   44 - 62   2018

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    Progress in the classification of C* algebras

    DOI: 10.11429/sugaku.0701044

  • Nuclear dimension and Z -stability Reviewed

    Yasuhiko Sato, Stuart White, Wilhelm Winter

    Inventiones Mathematicae   202 ( 2 )   893 - 921   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    Simple, separable, unital, monotracial and nuclear $$\mathrm {C}^{*}$$C∗-algebras are shown to have finite nuclear dimension whenever they absorb the Jiang–Su algebra $$\mathcal {Z}$$Z tensorially. This completes the proof of the Toms–Winter conjecture in the unique trace case.

    DOI: 10.1007/s00222-015-0580-1

  • Elementary amenable groups are quasidiagonal Reviewed

    Narutaka Ozawa, Mikael Rørdam, Yasuhiko Sato

    Geometric and Functional Analysis   25 ( 1 )   307 - 316   2015.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    We show that the group C*-algebra of any elementary amenable group is quasidiagonal. This is an offspring of recent progress in the classification theory of nuclear C*-algebras.

    DOI: 10.1007/s00039-015-0315-x

  • Ƶ-stability of crossed products by strongly outer actions II Reviewed

    Hiroki Matui, Yasuhiko Sato

    American Journal of Mathematics   136 ( 6 )   1441 - 1496   2014.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    We consider a crossed product of a unital simple separable nuclear stably finite Ƶ-stable C∗-algebra A by a strongly outer cocycle action of a discrete countable amenable group Γ. Under the assumption that A has finitely many extremal tracial states and Γ is elementary amenable, we show that the twisted crossed product C∗-algebra is Ƶ-stable. As an application, we also prove that all strongly outer cocycle actions of the Klein bottle group on Ƶ are cocycle conjugate to each other. This is the first classification result for actions of non-abelian infinite groups on stably finite C∗-algebras.

    DOI: 10.1353/ajm.2014.0043

  • Decomposition rank of UHF-absorbing c* -algebras Reviewed

    Hiroki Matui, Yasuhiko Sato

    Duke Mathematical Journal   163 ( 14 )   2687 - 2708   2014.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    Let Abe a unital separable simple C*-algebra with a unique tracial state. We prove that if A is nuclear and quasidiagonal, then A tensored with the universal uniformly hyperfinite (UHF) algebra has decomposition rank at most one. We then prove that A is nuclear, quasidiagonal, and has strict comparison if and only if A has finite decomposition rank. For such A, we also give a direct proof that A tensored with a UHF algebra has tracial rank zero. Using this result, we obtain a counterexample to the Powers-Sakai conjecture.

    DOI: 10.1215/00127094-2826908

  • Strict comparison and Z-absorption of nuclear C *-algebras Reviewed

    Hiroki Matui, Yasuhiko Sato

    Acta Mathematica   209 ( 1 )   179 - 196   2012.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1007/s11511-012-0084-4

  • Trace spaces of simple nuclear C*-algebras with finite-dimensional extreme boundary

    Yasuhiko Sato

    arXiv:1209.3000   2012.10

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    Language:English   Publishing type:Research paper (scientific journal)  

  • Z-Stability of Crossed Products by Strongly Outer Actions Reviewed

    Hiroki Matui, Yasuhiko Sato

    Communications in Mathematical Physics   314 ( 1 )   193 - 228   2012.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    We consider a certain class of unital simple stably finite C*-algebras which absorb the Jiang-Su algebra Z tensorially. Under a mild assumption, we show that the crossed product of a C*-algebra in this class by a strongly outer action of ℤ N or a finite group is Z -stable. As an application, we also prove that all strongly outer actions of ℤ 2 on Z are mutually cocycle conjugate.

    DOI: 10.1007/s00220-011-1392-9

  • Discrete amenable group actions on von Neumann algebras and invariant nuclear C*-subalgebras

    Yasuhiko Sato

    arXiv:1104.4339   2011.10

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    Language:English   Publishing type:Research paper (scientific journal)  

  • The Rohlin property for automorphisms of the Jiang-Su algebra Reviewed

    Yasuhiko Sato

    Journal of Functional Analysis   259 ( 2 )   453 - 476   2010.7

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    Language:English   Publishing type:Research paper (scientific journal)  

    For projectionless C*-algebras absorbing the Jiang-Su algebra tensorially, we study a kind of the Rohlin property for automorphisms. We show that the crossed products obtained by automorphisms with this Rohlin property also absorb the Jiang-Su algebra tensorially under a mild technical condition on the C*-algebras. In particular, for the Jiang-Su algebra we show the uniqueness up to outer conjugacy of the automorphism with this Rohlin property.

    DOI: 10.1016/j.jfa.2010.04.006

  • Certain aperiodic automorphisms of unital simple projectionless C* -algebras Reviewed

    Yasuhiko Sato

    International Journal of Mathematics   20 ( 10 )   1233 - 1261   2009.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    Let G be an inductive limit of finite cyclic groups, and A be a unital simple projectionless C*-algebra with K1(A) ≅ G and a unique tracial state, as constructed based on dimension drop algebras by Jiang and Su. First, we show that any two aperiodic elements in Aut(A)/WInn(A) are conjugate, where WInn(A) means the subgroup of Aut(A) consisting of automorphisms which are inner in the tracial representation. In the second part of this paper, we consider a class of unital simple C*-algebras with a unique tracial state which contains the class of unital simple A-algebras of real rank zero with a unique tracial state. This class is closed under inductive limits and crossed products by actions of with the Rohlin property. Let A be a TAF-algebra in this class. We show that for any automorphism α of A there exists an automorphism of A with the Rohlin property such that ∼ α and α are asymptotically unitarily equivalent. For the proof we use an aperiodic automorphism of the Jiang-Su algebra.

    DOI: 10.1142/S0129167X09005741

  • A generalization of the Jiang-Su construction

    Yasuhiko Sato

    arXiv:0903.5286   2009.7

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    Language:English   Publishing type:Research paper (scientific journal)  

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Professional Memberships

  • 日本数学会

Academic Activities

  • 主催者

    RIMS共同研究プログラム 「作用素環論における群作用と数理物理の関連」  ( Japan ) 2023.1

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    Type:Competition, symposium, etc. 

    Number of participants:50

Research Projects

  • Conditional Expectation on Operator Algebras and Applications of the Classification Strategy

    Grant number:24K06762  2024 - 2028

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

    佐藤 康彦

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    Authorship:Principal investigator  Grant type:Scientific research funding

    ある種の非可換な関係式(xy = yx が成立しない式)は有限次元の空間では表現しきれない. それらを無限次元の空間に表現する道具として作用素環と呼ばれる数学的対象が知られている. 本研究では作用素環(特にC*環)の分類理論から得られる成果を統一的に分類戦略としてまとめ, 数理物理や指数定理などへ応用する事が目的である. 実際, この方向性でPowers-Sakai予想やKirchbergの期待値問題などが解決できていた. 本研究ではこれらの散在的な成功例を線で繋ぐ何らかの統一的な視点を目指し, 具体的な分類戦略の応用として数理物理において古くから知られる相互モデルの問題を明らかにしたい.

    CiNii Research

  • 作用素環の核型次元の研究

    2020.6

  • Study on the nuclear dimension of operator algebras

    Grant number:19K03516  2019.4 - 2024.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

    佐藤 康彦

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    Grant type:Scientific research funding

    この研究では作用素環とよばれる無限次元の数学的対象から, ある種の有限な量を取り出す事が目的である. 作用素環は元々 J. von Neumann による量子力学の数学的な定式化に端を発し, 現在では非可換幾何学や自由確率論といった分野の母体となり, 様々な応用が得られてきた.
    <BR>
    本研究は作用素環の核型次元と呼ばれる数に焦点を絞り, 作用素環の分類定理を検証する国内初の研究課題である. 既に国内で盛んに研究されているvon Neumann 環論や群作用の技術を, 核型次元という新たな研究対象に活かすという点で, 今までに無い化学反応が起こり, 大きな結果へつながると期待する.

    CiNii Research

  • 作用素環の核型次元の研究

    2019 - 2022

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

  • 作用素環の分類理論と群や力学系への応用

    2015 - 2019

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (B)

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    Grant type:Scientific research funding

  • Jiang-Su 環の群作用の分類とその応用

    2013 - 2015

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Research Activity start-up

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    Grant type:Scientific research funding

  • 作用素環の自己同型と実数群作用の分類

    2011 - 2012

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (B)

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    Grant type:Scientific research funding

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Class subject

  • 解析学Ⅲ

    2024.10 - 2025.3   Second semester

  • 数理科学特別講義XⅢ

    2024.10 - 2025.3   Second semester

  • 数理科学特論13

    2024.10 - 2025.3   Second semester

  • 数学特論9

    2024.4 - 2024.9   First semester

  • 関数解析大意

    2024.4 - 2024.9   First semester

  • 解析学Ⅲ

    2023.10 - 2024.3   Second semester

  • 関数解析の基礎

    2023.10 - 2024.3   Second semester

  • 線形代数学Ⅱ

    2023.10 - 2024.3   Second semester

  • 微分積分学Ⅱ

    2023.10 - 2024.3   Second semester

  • 線形代数学Ⅰ

    2023.4 - 2023.9   First semester

  • 微分積分学Ⅰ

    2023.4 - 2023.9   First semester

  • 微分積分学Ⅱ

    2022.10 - 2023.3   Second semester

  • 線形代数学Ⅱ

    2022.10 - 2023.3   Second semester

  • コアセミナーⅡ

    2022.10 - 2023.3   Second semester

  • 関数解析大意

    2022.4 - 2022.9   First semester

  • 線形代数学Ⅰ

    2022.4 - 2022.9   First semester

  • 数学特論9(関数解析)

    2022.4 - 2022.9   First semester

  • 微分積分学Ⅰ

    2022.4 - 2022.9   First semester

  • 数理科学特別講義XⅣ

    2021.10 - 2022.3   Second semester

  • 微分積分学Ⅱ

    2021.10 - 2022.3   Second semester

  • コアセミナーⅡ

    2021.10 - 2022.3   Second semester

  • 数理科学特論14

    2021.10 - 2022.3   Second semester

  • 微分積分学Ⅰ

    2021.4 - 2021.9   First semester

  • 数学特論9(関数解析)

    2021.4 - 2021.9   First semester

  • 関数解析大意

    2021.4 - 2021.9   First semester

  • 線形代数学・同演習B

    2020.10 - 2021.3   Second semester

  • 微分積分学・同演習B

    2020.10 - 2021.3   Second semester

  • 線形代数学・同演習A

    2020.4 - 2020.9   First semester

  • 微分積分学・同演習Ⅲ

    2020.4 - 2020.9   First semester

  • 微分積分学・同演習A

    2020.4 - 2020.9   First semester

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FD Participation

  • 2021.7   Role:Participation   Title:数理学府FD

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2021.3   Role:Participation   Title:数理学府FD

    Organizer:[Undergraduate school/graduate school/graduate faculty]

Travel Abroad

  • 2015.4 - 2017.3

    Staying countory name 1:United States   Staying institution name 1:パーデュー 大学

    Staying countory name 2:Denmark  

    Staying countory name 3:United States  

  • 2013.4 - 2013.11

    Staying countory name 1:Denmark   Staying institution name 1:コペンハーゲン 大学

    Staying countory name 2:Denmark  

    Staying countory name 3:United States  

  • 2012.4 - 2012.10

    Staying countory name 1:United States   Staying institution name 1:オレゴン 大学

    Staying countory name 2:Denmark  

    Staying countory name 3:United States