RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) | iTHEMS

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Farewell message from Kan Kitamura

Our colleague, Kan Kitamura, will be joining the Department of Mathematics, College of Science, Rikkyo University as an Assistant Professor, starting April 1, 2026. We will all miss him and wish him the best of luck in this new endeavor. Here is a message from Kan Kitamura: <i>I joined iTHEMS as a special postdoctoral researcher (SPDR) in April, 2024. It has been a great pleasure to spend these two years in such a wonderful research environment. This department is built on a unique concept where researchers from diverse fields of theoretical science work together under one roof. Being able to casually interact with colleagues from different areas has continually stimulated my intellectual curiosity and provided me with a lot of inspiration. In 2025, iTHEMS transitioned into a center, and I feel fortunate to have been there at that time. The evolving environment kept my research experience fresh and exciting. I feel that my research has progressed well during my time here, and I have no doubt that the creative atmosphere of iTHEMS played a significant role in this. I would like to express my deep gratitude to my colleagues for the discussions, both formal and informal, and to the staff for their support. Although I will be leaving my current position, I will remain affiliated as a visiting scientist, and I hope to continue interacting with all of you. I wish iTHEMS every success and continued growth.</i>

2026-03-24
Team Director Motoko Kotani Receives the Japan Academy Prize

Motoko Kotani, Team Director (concurrent) of the Mathematical Application Research Team, Division of Applied Mathematical Science, at the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), has been selected as a recipient of the Japan Academy Prize. The Japan Academy announced on March 12, 2026, that the award recognizes the collaborative research “Discrete Geometric Analysis of Infinite Graphs with Symmetry” conducted with Toshikazu Sunada, Professor Emeritus of Meiji University and Professor Emeritus of Tohoku University. According to the award citation, the research was highly recognized for introducing the concept of the “standard realization” of crystal lattices, for studies of random walks on crystal lattices based on that concept, in particular for establishing central limit theorems and large deviation principles, and for the rediscovery of the K4 crystal and the promotion of its applications to materials science. These achievements have made important contributions to the development of discrete geometric analysis and discrete algebraic geometry from both theoretical and applied perspectives. The research recognized by this award is based on work that Team Director Kotani pursued while based at Tohoku University and the Advanced Institute for Materials Research (WPI-AIMR), Tohoku University. In 2018, iTHEMS and AIMR established the collaborative hub SUURI-COOL (Sendai): AIMR-iTHEMS Mathematical Science Laboratory. This laboratory, located on the third floor of the AIMR Main Building, aims to address fundamental questions in matter, life, and the universe, as well as basic problems in society, from the perspective of the mathematical sciences. All of us at iTHEMS extend our heartfelt congratulations to Team Director Kotani on this distinguished achievement.

2026-03-17
XIIIth International Symposium on Nuclear Symmetry Energy (NuSym25) on September 8-13, 2025

The XIIIth International Symposium on Nuclear Symmetry Energy (NuSym25) was held from September 8 to 13, 2025, at the Integrated Innovation Building, RIKEN Kobe Campus. The symposium brought together approximately 78 researchers working on nuclear physics, astrophysics, and related fields to discuss recent developments in the study of the nuclear equation of state (EoS) and nuclear symmetry energy. The nuclear symmetry energy plays an important role in understanding properties of neutron-rich nuclear matter, which is relevant for nuclear structure, heavy-ion collisions, and astrophysical phenomena such as neutron stars and their mergers. The symposium aimed to connect experimental, observational, and theoretical efforts across these areas. The scientific program included invited and contributed talks covering a broad range of topics, including nuclear structure and reactions, heavy-ion collision experiments and transport model simulations, microscopic calculations of dense neutron-rich matter, and astrophysical observations of compact stars. Recent progress in multi-messenger observations of neutron stars and their implications for the nuclear equation of state were also discussed. The symposium provided an opportunity for researchers from different communities to exchange ideas and strengthen collaborations in addressing common challenges related to the nuclear equation of state. Following the main scientific sessions, a meeting of the Transport Model Evaluation Project (TMEP) was held to discuss benchmarking and uncertainty quantification in transport model simulations for heavy-ion collisions. Reported by Shuntaro Aoki

2026-03-11
RIKEN–Nara Women’s University Joint Diversity Promotion Workshop 2026 was held

Students from various courses at Nara Women’s University—including mathematics, physics, chemistry, biological sciences, and environmental sciences—visited RIKEN for two days, March 2–3. A total of 21 students (first-, second-, and third-year undergraduate students and first-year master’s students) participated in the visit. During their stay, the students toured several research facilities at RIKEN, including the Multiscale Brain Function Research Team at the RIKEN Center for Brain Science (CBS), the RIBF facility at the RIKEN Nishina Center, and the Optical Quantum Control Research Team at the RIKEN Center for Quantum Computing (RQC). At iTHEMS, they attended talks by Megumi Oya (Postdoctoral Researcher, Medical Science Data-driven Mathematics Team, iTHEMS) and Leo Speidel (iTHEMS ECL Research Unit Leader). At each laboratory, the students had the opportunity to observe cutting-edge research up close near experimental equipment and learn about ongoing research activities. During the evening networking session with RIKEN researchers, they asked questions to iTHEMS researchers and learned about researchers’ daily lives and career paths. The event provided a valuable opportunity for meaningful交流 and discussion for the students. This diversity promotion initiative is conducted jointly by the Faculty of Science at Nara Women’s University and RIKEN iTHEMS, and is organized in conjunction with a series of lectures held at Nara Women’s University.

2026-03-09
RIKEN President Makoto Gonokami Visits the RIKEN Berkeley Center

On February 26, 2026, Makoto Gonokami, President of RIKEN, visited the RIKEN Berkeley Center (Photo left). During his visit, the Center’s mission and organizational concept were introduced, followed by a tour of the office facilities. President Gonokami then met with the RIKEN Berkeley Fellows currently conducting research in UC Berkeley (UCB) and Lawrence Berkeley National Laboratory (LBNL) (Photo right). The fellows presented overviews of their research projects and shared their experiences regarding the academic and living environment in Berkeley. They highlighted the stimulating research atmosphere and discussed their perspectives for further development. Before and after the Center visit, President Gonokami also exchanged views with Steve Kahn (UCB, Dean of Mathematical and Physical Sciences), Yasunori Nomura（UCB, Director of the Leinweber Institute for Theoretical Physics）, and Hitoshi Murayama (UCB, Professor, Physics Department), and toured quantum computing facilities at Berkeley. This visit is expected to further strengthen collaboration and researcher exchange between RIKEN and Berkeley. The RIKEN Berkeley Center will continue to promote academic partnership and serve as a hub for international research collaboration. <small>Photo left: In front of the RIKEN Berkeley Center signboard. From left to right: Center Director Iso, RIKEN President Makoto Gonokami, Wick Haxton, RIKEN Berkeley Center Director Nagataki, and Domain Director Hatsuda. Photo right: President Gonokami in discussion with RIKEN Berkeley Fellows. From left to right: Gabriele Di Ubaldo, Jan Shuette-Engel, Yuka Kanakubo, Domain Director Hatsuda, and Center </small>

2026-03-04
Nagisa Hiroshima Receives the 7th (2026) Fumiko Yonezawa Memorial Prize

Nagisa Hiroshima (Visiting Scientist, iTHEMS / Associate Professor, Yokohama National University) has received the 7th (2026) Fumiko Yonezawa Memorial Prize. The Fumiko Yonezawa Memorial Prize was established by the Physical Society of Japan to recognize and encourage outstanding research achievements by early- to mid-career women physicists. In principle, the prize is awarded to researchers within 15 years of obtaining their final degree, and each year a small number of recipients (approximately five) are selected. Hiroshima has been engaged in theoretical research on dark matter, using astrophysical observations and theoretical models to investigate its properties. Her series of research achievements in dark matter studies employing astrophysical approaches was highly recognized, leading to this award. Congratulations, Nagisa!

2026-02-05
“Black Hole Recorder” Exhibited in “Mission ∞ Infinity | Space + Quantum + Art”

ADK Marketing Solutions Inc. is exhibiting the interactive science-art installation “Black Hole Recorder”, created in collaboration with iTHEMS, as part of the special exhibition “Mission ∞ Infinity | Space + Quantum + Art”, currently being held at the Museum of Contemporary Art Tokyo from January 31 to May 6, 2026. This work is a prototype model of a future information storage device inspired by quantum black hole theory. Using the black hole as a metaphor for an object capable of containing enormous amounts of data, the installation invites visitors to record human voices and sounds, imagining them being delivered into the distant future or even into space. Through artworks that merge space science, quantum theory, and artistic expression, the exhibition offers a unique opportunity to experience the invisible world and explore new possibilities for the future. For more information, please see the related links.

2026-02-03
A New Principle for Controlling the “Butterfly Effect”

Takemasa Miyoshi (Team Principal, Data Assimilation Research Team, RIKEN Center for Computational Science (R-CCS) / Team Director, Prediction Science Research Team, Division of Applied Mathematical Science, RIKEN iTHEMS), has developed a new mathematical framework for efficiently controlling chaos by turning the fundamental limitation of predictability in deterministic chaos—widely known as the “butterfly effect”—to an advantage. He proposed a “duality principle,” demonstrating that data assimilation, which forms the foundation of weather forecasting (a process that synchronizes a model with the behavior of nature using observational data), and the control of chaos are mathematically twin concepts. Rather than suppressing chaos itself, this new approach exploits the high sensitivity characteristic of chaotic systems to synchronize real-world behavior with a manageable “target trajectory” through only a small amount of “intervention.” In this way, the study theoretically outlines a path toward controlling chaos beyond the conventional limits of predictability. This achievement provides a theoretical basis for future research in disaster prevention and mitigation—for example, applying minimal interventions to synchronize real atmospheric phenomena with a “typhoon scenario that causes no damage” (a target trajectory) simulated in a model, with the aim of avoiding extreme weather events. It is also expected to have applications in a wide range of fields that exhibit chaotic behavior, including ecosystems and economics. For further details, please refer to the related links.

2026-01-15
A 300-Billion-Particle Milky Way Simulation Achieved with AI × Fugaku

An international collaborative research team including Keiya Hirashima, Special Postdoctoral Researcher, has achieved the world’s highest-resolution simulation of the Milky Way galaxy by utilizing the entire system of the AI and supercomputer “Fugaku” (approximately 150,000 nodes) and modeling 300 billion particles representing stars, interstellar gas, and other components—resolving the galaxy down to individual stars. This research is expected to contribute to a better understanding of the Milky Way’s spiral arm structure (the arm-like features of spiral galaxies that extend outward from the center while winding across the galactic disk), the circulation of chemical elements within the galaxy, and the origins of the materials that formed the Solar System and life. For more details, please refer to the related links.

2026-01-15
RIKEN–IBS Joint Workshop on Mathematical Approaches to Nature Held in Daejeon, Korea, December 9–12, 2025

In December 9–12, 2025, a collaborative workshop jointly organized by the Institute of Basic Science (IBS, Korea) and RIKEN was held in Daejeon, Korea. The workshop aimed to explore the unifying mathematical principles that underlie diverse natural phenomena—from the fundamental interactions that shape the universe to the complex behaviors observed in living systems. From RIKEN, iTHEMS researchers including Derek Inman, Ryo Namba, Alvaro Pastor Gutierrez, Shuntaro Aoki, Sungsik Kong, Amaury Micheli, Puttarak Jai-akson, Ryoko Oishi-Tomiyasu, Che-Yu Chen, and Christy Kelly delivered talks. All the presentations were impressive and thoughtfully prepared so that researchers from different fields could follow and appreciate the content. Indeed, there were many stimulating cross-disciplinary questions, and we enjoyed lively discussions over lunches and dinners, accompanied by excellent (and wonderfully spicy) food. Although the workshop was originally designed to foster collaboration between RIKEN and IBS, connections were already present—for example, through Shuntaro Aoki, a physicist at iTHEMS formerly at IBS, and Shingo Gibo, a mathematical biologist at IBS formerly at iTHEMS. This workshop further strengthened these ties and created new ones. The planning and local organization of the workshop were led by the center of Masahide Yamaguchi (IBS), Yusuke Yamada (IBS), and by Yuto Yamamoto and Ryo Namba at RIKEN iTHEMS, with strong support from IBS and the International Collaboration Section of the Global Strategy Division at RIKEN. We are deeply grateful for their dedicated efforts. I hope that the successful interactions fostered through this workshop will continue to develop even further. (Photos: courtesy of Director Satoshi Iso, RIKEN iTHEMS.) Reported by Gen Kurosawa

2026-01-08

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RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) is an international research center at RIKEN. It facilitates close collaborations among researchers from different disciplines in theoretical, mathematical and computational sciences. On April 1, 2025, iTHEMS transitioned from a program to a center. The ultimate goal of iTHEMS is to unravel the mystery of the Universe, matter, and life, as well as to solve key problems in modern society through interdisciplinary approaches.

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Director: Satoshi Iso

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Visiting

Almudena Sánchez Guillén

Ph.D. Student, Institute of Structure of Matter (IEM-CSIC), Spain

Term: February 2 (Mon) - April 30 (Thu) 2026

Visiting Place: Main Research Building, RIKEN Wako Campus
Gordon Baym

Senior Visiting Scientist, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) / Professor Emeritus, University of Illinois, USA

Term: April 3 (Fri) - May 1 (Fri) 2026

Visiting Place: Main Research Building, RIKEN Wako Campus