Hiroto Nishikawa

Hiroto Nishikawa (西川 寛人) is a Japanese mathematician working in operator algebra theory. He is a JSPS Research Fellow (DC2) at Kyoto University's Research Institute for Mathematical Sciences (RIMS), in the group of Narutaka Ozawa, and holds a KAKENHI grant (26KJ1456) on the analytic properties of infinite graphs and their associated operator algebras. Before university he was selected for Japan's six-member team at the 59th International Mathematical Olympiad (IMO 2018, Cluj-Napoca, Romania), where he won a bronze medal while a grade-3 student at Aichi Prefectural Meiwa High School. He entered Kyoto University in 2019 and progressed through its mathematics programme to a PhD. His 2024 arXiv paper, C*-exactness and property A for group actions, characterises property A of Schreier graphs via exactness of the generated C*-algebra.

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• Represents Japan at the 59th IMO (2018, Cluj-Napoca, Romania) as a grade-3 student at Aichi Prefectural Meiwa High School (Aichi), winning a bronze medal with 18 points (7-7-0-2-1-1), rank 228.Jul 13, 2018
• By 2026 is a JSPS Research Fellow (DC2) at RIMS, Kyoto University, leading KAKENHI project 26KJ1456 'Analytic properties of infinite graphs and associated operator algebras' (2026-04-22 to 2028-03-31). A DC2 fellowship at PhD stage signals a top-tier research trajectory.Apr 22, 2026
• One of only two public-school students on Japan's 2018 IMO team, and the only bronze medallist from a public high school - the other five medalists came from elite private schools (Nada, Kaisei, Tsukuba Komaba, Rakunan). Steeled a route from a public school into top-tier Japanese mathematics.Jul 17, 2018
• PhD student (D2 as of the 2024-25 academic year) in Narutaka Ozawa's group at RIMS; Ozawa is one of the world's leading operator algebraists, so his placement ties him into Japan's strongest operator-algebra centre.2025
• Authored 'C*-exactness and property A for group actions' (arXiv 2407.16130, 2024), showing the Schreier graph of a group action has property A iff the permutation representation generates an exact C*-algebra - work that generalizes Sako's theorem.Jul 23, 2024
• Institutional email [contact omitted] (handle 'hnishika') published on the RIMS institute email convention page.2026
• Personal site https://sites.google.com/view/hnishikawa/home listed on the RIMS graduate-students page under the handle 'hnishika'.2026