Takuya Takeishi

Associate Professor, Kyoto Institute of Technology

e-mail: takeishi at kit.ac.jp

Reserch interest: Operator algebras from number theory, KMS-states, groupoid C*-algebras.

Supported by JSPS KAKENHI Grant Number 24K06780 (2024-2026)
Previous KAKENHI

Research map

Schedules

Courses

• April 2025 - , Mathematical Statistics (Wed. 10:30-12:00).
• April 2025 - , Calculus I (Thu. 8:50-10:20).
• April 2025 - , Calculus I (Thu. 10:30-12:00).
• April 2025 - , Studies in Applied Analysis (Tue. 12:50-14:20), with Takuya Mine, Yasuki Isozaki, Takahiro Mori.
• April 2025 - , Seminar on analysis (Thu. 16:10-17:40), with Takuya Mine.
• April 2025 - , Mathematical Sciences Ia (Mon. 16:10-17:40) (1st Quarter)
• October 2025 - , Mathematical Analysis and its Applications (Thu. 10:30-12:00)

Past Courses

Publications

1. T. Takeishi, On Nuclearity of C*-algebras of Fell Bundles over Étale Groupoids, Publications of the Research Institute for Mathematical Sciences 50, no.2, 251-268. (2014) published version arXiv version
2. T. Takeishi, Irreducible Representations of Bost-Connes systems, Journal of Noncommutative Geometry 10, no. 3, 889-906. (2016) published version arXiv version
   (Note : For arXiv version, the current version is 2. Several mistakes of notations are revised and section numbers are changed.)
3. T. Takeishi, Bost-Connes systems for local fields of characteristic zero, International Mathematics Research Notices IMRN 2018, no. 7, 2052-2069 (2018). published version arXiv version
4. T. Takeishi, Primitive ideals and K-theoretic approach to Bost-Connes systems, Advances in Mathematics 302, 1069-1079. (2016) published version arXiv version
   (Note : For arXiv version, the current version is 2. Proposition 3.6, Remark 3.13, and several minor revisions are added.)
5. Y. Kubota and T. Takeishi, Reconstructing the Bost--Connes semigroup actions from K-theory, Advances in Mathematics 366 (2020) published version arXiv version
   (Page number will be added later.)
6. C. Bruce, M. Laca and T. Takeishi, Partition functions as C*-dynamical invariants and actions of congruence monoids, Communications in Mathematical Physics 382, no.2, 1165–1203. (2021) published version arXiv:1911.00793
   (Note : For arXiv version, the current version is 2. )
7. C. Bruce and T. Takeishi, C*-dynamical invariants and Toeplitz algebras of graphs (2021), to appear in J. Operator Theory arXiv:2103.02816
8. T. Takeishi, Limits of KMS states on Toeplitz algebras of finite graphs, Journal of Operator Theory 90, no. 2, 545–568. (2023) arXiv:2108.08431
9. C. Bruce and T. Takeishi, Constructing number field isomorphisms from *-isomorphisms of certain crossed product C*-algebras, Communications in Mathematical Physics 405, 20 (2024). published version (open access)
10. C. Bruce and T. Takeishi, On the C*-algebra associated with the full adele ring of a number field (2022), Journal of Noncommutative Geometry, 19, no. 2, pp. 383–399 (2025). published version (open access)
11. C. Bruce, Y. Kubota, and T. Takeishi, Groupoid homology and K-theory for algebraic actions from number theory (2024), arXiv:2407.01952
12. C. Bruce, X. Li, and T. Takeishi, Boundary actions of outer automorphism groups of Thompson-like groups (2025), arXiv:2512.14324

Other articles

1. 武石拓也，作用素環論と数論，「数理科学」2019年12月号掲載

Talks

1. On Nuclearity of C*-algebras of Fell Bundles over Étale Groupoids, Operator Algebra Seminar, Tokyo, April, 2013
2. On Nuclearity of C*-algebras of Fell Bundles over Étale Groupoids, Recent Developments in Operator Algebras, Kyoto, September, 2013
3. On Class Field Theory, Conference of Functional Analysis, Kusatsu, September, 2013
4. On Nuclearity of C*-algebras of Fell Bundles over Étale Groupoids, MSJ Autumn Meeting 2013, Ehime, September, 2013
5. Bost-Connes system for local fields of characteristic zero, C*-algebra seminar, Oslo, January, 2014
6. Bost-Connes system for local fields of characteristic zero, Operator Algebra Seminar, Tokyo, April, 2014
7. Bost-Connes system for local fields of characteristic zero, ICM Satellite Conference on Operator Algebra and Applications, Korea, August, 2014
8. On Bost-Connes Systems, Conference of Functional Analysis, Gifu, August, 2014
9. Bost-Connes system for local fields of characteristic zero, MSJ Autumn Meeting 2014, Hiroshima, September, 2014
10. Bost-Connes system for local fields of characteristic zero, The Second China-Japan Conference on Noncommutative Geometry and K-Theory, Okinawa, October, 2014
    Slides
11. Irreducible Representations of Bost-Connes systems, Number theory and non-commutative geometry, Bonn, November, 2014
    Video on Youtube
12. Irreducible Representations of Bost-Connes systems, Workshop on Operator Theory and Operator Algebras, Tokyo, December, 2014
13. Irreducible Representations of Bost-Connes systems, Kyoto Operator Algebra Seminar, Kyoto, March, 2015
14. Irreducible Representations of Bost-Connes systems, Oberseminar, Münster, June, 2015
15. Irreducible Representations of Bost-Connes systems, Oberwolfach, June, 2015
16. Primitive Ideals of Bost-Connes C*-algebras, Geometry and Analysis seminar, London, September, 2015
17. On the classification problem of Bost-Connes systems, Operator Algebra Seminar, Copenhagen, October, 2015
18. Primitive ideals and K-theoretic approach to Bost-Connes systems, Münster, December, 2015
19. Primitive ideals and K-theoretic approach to Bost-Connes systems, Victoria, March, 2016
20. Primitive ideals and K-theoretic approach to Bost-Connes systems, Kyoto Operator Algebra Seminar, Kyoto, July, 2016
21. On the condition C^*_(G)=C^*_r(G) for étale groupoids (after R. Willett), Conference of Functional Analysis, Kusatsu, August, 2016
22. Primitive ideals and K-theoretic approach to Bost-Connes systems, Recent Developments in Operator Algebras, Kyoto, September, 2016
23. Primitive ideals and K-theoretic approach to Bost-Connes systems, MSJ Autumn Meeting 2016, Osaka, September, 2013
24. On the classification of Bost-Connes C*-algebras, Geometry and Analysis seminar, London, January, 2017
25. On the classification problem of Bost-Connes systems, Analysis Seminar, Sapporo, 2017
26. Basics of K-theory, Conference of Functional Analysis, Nara, August, 2017
27. Reconstructing the Bost-Connes semigroup actions from K-theory, Recent Developments in Operator Algebras, Kyoto, September, 2017
28. Reconstructing the Bost-Connes semigroup actions from K-theory, Facets of Irreversibility: Inverse Semigroups, Groupoids, and Operator Algebras, Oslo, Norway, December, 2017
29. Reconstructing the Bost-Connes semigroup actions from K-theory, Mathematical study on topological phases, RIMS, Kyoto, Japan, January 2018
30. Reconstructing the Bost-Connes semigroup actions from K-theory, MSJ Spring Meeting 2018, Tokyo, Japan, March, 2018
31. Reconstructing the Bost-Connes semigroup actions from K-theory. I, Operator theory seminar, Victoria, Canada, September, 2018
32. Reconstructing the Bost-Connes semigroup actions from K-theory. II, Operator theory seminar, Victoria, Canada, September, 2018
33. Reconstructing the Bost-Connes semigroup actions from K-theory, Geometry and Analysis Seminar, London, UK, October, 2018
34. Reconstructing the Bost-Connes semigroup actions from K-theory. I, Workshop on Operator Theory and Operator Algebras, Shizuoka, December, 2018
35. Reconstructing the Bost-Connes semigroup actions from K-theory. II, Workshop on Operator Theory and Operator Algebras, Shizuoka, December, 2018
36. Reconstructing the Bost-Connes semigroup actions from K-theory, Young mathematicians workshop on algebraic, geometric, and analytic aspects of K theory and vector bundles, Okinawa, August, 2019
37. C*-dynamical invariants for actions of congruence monoids (in preparation), Operator theory seminar, Victoria, Canada, September, 2019
38. Partition functions as C*-dynamical invariants and actions of congruence monoids, Kyoto Operator Algebra Seminar, Kyoto, 2019
39. Partition functions as C*-dynamical invariants and actions of congruence monoids, 作用素環の分類理論における新展開, RIMS, Kyoto, Japan, 2020
40. Partition functions as C*-dynamical invariants and actions of congruence monoids, MSJ Spring Meeting 2020, Tokyo, March, 2020
    (This conference is canceled, but this talk shall be deemed held. See here (Japanese))
41. Partition functions as C*-dynamical invariants and actions of congruence monoids, Tokyo-Kyoto Operator Algebra Seminar, Online, May, 2020
42. Operator Algebras and Number Theory, Conference of Functional Analysis, Online, September, 2020
43. Partition functions as C*-dynamical invariants and actions of congruence monoids, CMS Winter Meeting 2020, Online (Canada), December, 2020
44. Partition functions as C*-dynamical invariants and actions of congruence monoids, 作用素環と量子力学系, Online (RIMS Kyoto), February, 2021
45. C*-dynamical invariants and Toeplitz algebras of graphs (part 2 of 2), Operator Algebra and Noncommutative Geometry seminar, Online (Wollongong, Australia), March, 2021
46. KMS states of Toeplitz algebras of graphs, Tokyo-Kyoto Operator Algebra Seminar, Online, June, 2021
47. KMS states of Toeplitz algebras of graphs, 第60回実函数論・函数解析学合同シンポジウム, Online, September, 2021
48. Constructing number field isomorphisms from *-isomorphisms of certain crossed product C*-algebras, Kyoto Operator Algebra Seminar, Kyoto, April, 2022
49. Constructing number field isomorphisms from *-isomorphisms of certain crossed product C*-algebras, MSJ Autumn Meeting 2022, Sapporo, September, 2022
50. Constructing number field isomorphisms from *-isomorphisms of certain crossed product C*-algebras, Tokyo Operator Algebra Seminar, October, October, 2022
51. Rigidity theorems of certain classes of C*-algebras from number theory I-III, 作用素環論における群作用と数理物理の関連, Kyoto, January, 2023
52. Rigidity theorems of C*-algebras arising from number theory, Low dimensional topology and number theory XIV, Fukuoka, March, 2023
53. C*-algebras constructed from number fields and related complete invariants of number fields (invited talk), MSJ Spring Meeting 2024, Osaka, March, 2024
54. Groupoid homology and K-theory for algebraic actions from number theory, Semigroups, groupoids, and C*-algebras, KIAS, Seoul, Korea, July, 2024
55. Groupoid homology and K-theory for algebraic actions from number theory, China-Japan-Korea Conference on Functional Analysis, Harbin, China, August, 2024
56. Groupoid homology and K-theory for algebraic actions from number theory, Analysis Seminar, Newcastle, UK, October, 2024
57. Groupoid homology and K-theory for algebraic actions from number theory, Groups, operator algebras, and topological dynamics, Newcastle, UK, September, 2025
58. Groupoid homology and K-theory for algebraic actions from number theory, 作用素論作用素環論研究集会2025, Nagoya, Japan, November, 2025

Poster Sessions

1. Irreducible Representations of Bost-Connes systems, Future directions for non-commutative geometry, Bonn, December, 2014

C.V.