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評判に基づいた協力を支える仕組みを新たに発見

理化学研究所数理創造研究センター（iTHEMS）の村瀬洋介チームディレクターを含む国際共同研究チームは、評判に基づく協力行動の進化を可能にする新たな仕組みを理論的に明らかにしました。人間社会では、他者の評判をもとに協力するかどうかを判断する「間接互恵性」が、協力関係を支える重要な仕組みの一つと考えられています。一方、同じ人に対する評価が人によって異なる場合、社会の中で協力を維持することが難しくなることが、これまでの研究で課題となっていました。本研究では、従来のように「その人が他者に協力したか」だけでなく、「その人が他者から協力されたか」についても評判に反映する「二重評判更新」という仕組みを導入しました。その結果、この単純な拡張によって人々の評価の食い違いが抑えられ、協力が大幅に維持されやすくなることを、数理解析とコンピュータシミュレーションによって明らかにしました。本成果は、評判を通じて協力が生まれ、維持される仕組みへの理解を深めるとともに、同調、協力、排斥など、実社会における集団行動を理解する新たな手がかりとなることが期待されます。研究成果は、2026年8月28日に国際学術誌 Proceedings of the National Academy of Sciences (PNAS) に掲載予定です。

2026-08-25
Farewell message from Sungsik Kong

Our colleague, Sungsik Kong, will be joining Sejong University in South Korea as a tenure-track Assistant Professor in September 2026. We will all miss him and wish him every success in this exciting new chapter. Here is a message from Sungsik: <i>I joined iTHEMS in August 2025, and over the past year I have had the privilege of working in an exceptional research environment. Starting in September 2026, I will be joining Sejong University in South Korea as a tenure-track Assistant Professor. While I am excited about this move, I am also sad to be leaving my position as a Research Scientist at iTHEMS.</i> <i>My time at RIKEN has been both challenging and incredibly rewarding. I am deeply grateful to RIKEN and iTHEMS for giving me the opportunity to pursue the scientific questions I am passionate about. I will miss iTHEMS' collaborative atmosphere. I have had the chance to learn from researchers across many different fields, many that I would never have had the opportunity to explore otherwise. Those seminars, colloquiums, and conversations have broadened my perspective, sparked new ideas, and made my time here truly valuable and memorable.</i> <i>If you ever visit Seoul, please don't hesitate to get in touch. Thank you all so much. It has been a real pleasure.</i>

2026-08-17
Using chaos and symmetry to bootstrap quantum gravitational wormholes

An international research collaboration between Gabriele Di Ubaldo (RIKEN-Berkeley Center at UC Berkeley and RIKEN iTHEMS), Jan Boruch (University of California, Berkeley, US), Felix M. Haehl (University of Southampton, UK), Eric Perlmutter (Université Paris-Saclay and Institut des Hautes Études Scientifiques, France), and Moshe Rozali (University of British Columbia, Canada) published the new study in <em>Physical Review Letters</em>. Random matrix theory provides a universal description of chaos in quantum systems, capturing statistical patterns among energy levels without requiring knowledge of microscopic details. The new challenge addressed is its extension to 2D Conformal Field Theories and their holographically dual 3D quantum gravity via the AdS₃/CFT₂ correspondence. In the AdS₃/CFT₂ correspondence, quantum gravity in a three-dimensional negatively curved spacetime is encoded in a two-dimensional conformal field theory on its boundary. The key difference is <strong>modular invariance</strong>, a symmetry stating that a theory on a 2D torus is invariant under modular transformations, which imposes stringent constraints and a rigid mathematical structure, seemingly incompatible with quantum chaos and random matrix theory. Building on the 2023 work of Di Ubaldo and Perlmutter, “AdS₃/RMT₂ duality”, the researchers developed a general, nonperturbative framework called RMT₂ that uplifts the correlations of any random matrix model into fully modular-invariant quantities. The team then used RMT₂ to predict quantum amplitudes for 3D wormholes with multiple torus-shaped boundaries. A wormhole is a tunnel-like geometric connection between otherwise separate regions or boundaries of spacetime. While it is not a shortcut for interstellar travel as in sci-fi movies, it encodes deeply quantum information about gravity and black holes. For the three-boundary wormhole, the team also performed a gravity calculation that agrees with the RMT₂ prediction. By turning the earlier AdS₃/RMT₂ proposal into a general framework, the study advances a research direction that Gabriele helped pioneer and provides a new tool for probing black-hole microstates and, in the near future, solving AdS₃ quantum gravity. For further details, please see the article in <em>Physical Review Letters</em>.

2026-08-07
Riccardo Muolo Awarded Third Place at Falling Walls Lab Tokyo 2026

Riccardo Muolo awarded 3rd Place at Falling Walls Lab Tokyo, Japan Riccardo Muolo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, iTHEMS) took part in the Falling Walls Lab Tokyo, Japan, held on 28 July 2026 at Shibuya Sakura Stage, and was awarded 3rd Place by the jury. The Falling Walls Lab is an international pitch and science-communication competition hosted by the Falling Walls Foundation, a Berlin-based non-profit founded in 2009 on the twentieth anniversary of the fall of the Berlin Wall. The Foundation channels the spirit of that night to ask a recurring question — which are the next walls to fall in science and society — and works to make breakthrough ideas accessible across borders and disciplines. Open to students and early-career professionals of all disciplines and nationalities, the Lab invites participants to pitch their research, business model, or innovative idea in just three minutes, in front of their peers and a jury from academia and business. Academic institutions around the world are invited to host their own Falling Walls Lab and send their winners to the Falling Walls Lab Finale in Berlin, where the Finalists compete for the title of Breakthrough Winner in the Emerging Talents category and the chance to pitch again on the main stage of the Falling Walls Science Summit. This year’s Tokyo edition was organized by EURAXESS Japan, the German Centre for Research and Innovation (DWIH) Tokyo, and Tobitate! Japan. Riccardo’s research covers nonlinear dynamics on networks and higher-order structures, synchronization, Turing pattern formation, and the control of dynamical systems — exactly the kind of cross-disciplinary work the Falling Walls Lab is designed to showcase. Distilling it into a compelling three-minute pitch and earning recognition among a strong international field of participants is a fine achievement. Congratulations, Riccardo!

2026-08-07
原子検出回数の異常ゆらぎと普遍性の発見

大阪公立大学大学院理学研究科の山本和樹講師と、理化学研究所開拓研究所の濱崎立資理研白眉研究チームリーダー（理化学研究所数理創造研究センター上級研究員）は、多数の原子からなる量子多体系を連続的に測定した際に、原子の検出回数のゆらぎが、測定の強さによって大きく変化することを理論的に明らかにしました。測定が弱い場合には、原子の検出回数は標準的なゆらぎを示す一方で、測定が強い場合には、通常よりも大きな「異常ゆらぎ」が現れることを発見しました。詳細は大阪公立大学のホームぺ―ジをご覧ください。

2026-08-06
2026 iTHEMS Visit by the National Sun Yat-sen University, Taiwan

On June 25, a group of 3 professors and 13 students from National Sun Yat-sen University, Taiwan, visited RIKEN . The purpose of the visit was to immerse the students in RIKEN’s multidisciplinary research environment and introduce them to stateoftheart scientific methodologies. It also aimed to inspire their future research careers while exploring opportunities for academic exchange and longterm collaboration between both institutions. First, the group visited RIKEN Nishina Center for Accelerator-Based Science, hosted by Dr Claudio Santonastaso & Dr Seiya Sakai. Next visit was RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), hosted by Dr. Gen Kurosawa. Last visit was RIKEN Center for Quantum Computing, hosted by Dr. Franco Nori. Gen Kurosawa, Senior Research Scientist, introduced iTHEMS’s interdisciplinary research environment and explained how mathematical methods from physics can be applied to important questions in biological clocks, leading to testable predictions that are verified experimentally.

2026-07-29
Farewell message from Puttarak Jai-akson

Our colleague, Puttarak Jai-akson, will be joining the Graduate School of Science, Kyoto University, as a Program-Specific Researcher, starting in August 2026. We will all miss him and wish him every success in this exciting new chapter. Here is a message from Puttarak: <i>I would like to share that I will be leaving my position as a Postdoctoral Researcher at iTHEMS.</i> <i>I joined iTHEMS in November 2022, and after nearly four wonderful years, I will be moving to a new position as a Researcher at Kyoto University, starting in August 2026.</i> <i>During my time at iTHEMS, I greatly enjoyed the open, friendly, and interdisciplinary research environment. The opportunity to interact with researchers from diverse fields has broadened my perspective, inspired many new ideas, and significantly enriched my research. I am deeply grateful to all the members of iTHEMS for their support, encouragement, and the many enjoyable discussions we have shared. I would also like to express my heartfelt thanks to our wonderful iTHEMS Assistants, whose kindness, professionalism, and constant support made my time at iTHEMS all the more enjoyable.</i> <i>Although I am leaving my full-time position, I am pleased to continue my affiliation with iTHEMS as a Visiting Scientist. I sincerely hope to continue our discussions and collaborations in the future.</i> <i>If you happen to visit Kyoto University, please don't hesitate to let me know. I would be very happy to catch up and continue our conversations.</i> <i>Thank you all very much for everything. It has been a privilege to be part of iTHEMS, and I wish everyone continued success.</i>

2026-07-24
2026 iTHEMS Visit by the University of California San Diego Global Seminar Program

On July 8, Dr. Stanley Lo, Teaching Professor in the Department of Cell and Developmental Biology at the School of Biological Sciences, UCSD, visited iTHEMS together with 24 undergraduate students. The purpose of the visit was to learn about iTHEMS and its research activities while supporting the students’ learning about human diversity and the relationship between science and society. Thomas Hitchcock, Research Scientist at iTHEMS, hosted the lecture. He introduced his academic and professional background and presented his current research on evolution, ecology, and genetics.

2026-07-16
自然法則に現れる「自由に選べる数」の由来に迫る－量子重力における自由パラメータの謎に新たな手掛かり－

楠亀裕哉 iTHEMS客員研究員(本務: 九州大学高等研究院准教授）を含む国際共同研究グループは、2つの共形場理論を「界面」でつなぐ状況を解析しました。その結果、界面をわずかに動かしたときの応答を適切に取り出すと、2つの理論の違いを生む局所的な演算子が得られることを示し、それを具体的に構成する方法を与えました。今回の成果は、「量子重力には外から自由に選べる連続パラメータが存在しない」という予想を裏付けるものとなっており、量子重力の根本問題の理解につながると期待されます。詳細は九州大学のプレスリリースをご覧ください。

2026-06-24
The First RIKEN Quantum International Workshop on Frontiers of Quantum Computing Applications and Quantum-HPC Integration on May 25-26, 2026

The First RIKEN Quantum International Workshop on Frontiers of Quantum Computing Applications and Quantum–HPC Integration was held from May 25 to 26 at the Large Conference Room on the 2nd floor of the Administrative Headquarters, RIKEN Wako Campus. The workshop featured an entirely invited program, consisting of 13 plenary presentations (40 minutes each) and 9 highlight presentations (20 minutes each). The presentations covered a broad range of fields—including quantum chemistry, life sciences, condensed matter physics, atomic physics, and high-energy physics—with a primary focus on the theme of quantum–HPC hybrid integration. With more than 130 registered participants, each presentation was followed by lively and engaging discussions. Furthermore, the networking reception held on the evening of the first day was well-attended, fostering active interaction and collaboration among researchers from universities, national research institutes, and private industries. This workshop is expected to drive further advancements in quantum computing through quantum–HPC hybrid integration. Reported by Shinichiro Fujii

2026-06-11

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数理創造研究センター（RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences, 略称 iTHEMS アイテムス）は、理論科学・数学・計算科学の研究者が分野の枠を越えて基礎研究を推進する、国際研究拠点です。2025年4月1日にプログラムからセンターへと組織改編されました。iTHEMSでは、「数理」を軸とする分野横断的手法により、宇宙・物質・生命の解明や、社会における基本問題の解決を目指しています。

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Yang-Yang Tan

東京大学大学院理学系研究科知の物理学研究センター博士研究員

期間: 2026年5月1日(金) - 2027年4月30日(金)

来訪場所: 理化学研究所和光キャンパス研究本館
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Victor Kawasaki-Borruat

Doctoral Student, Doctoral Program in Electrical Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland

期間: 2026年8月3日(月) - 9月4日(金)

来訪場所: 理化学研究所和光キャンパス研究本館
Bowen Yang

Postdoctoral Fellow, Harvard University, USA

期間: 2026年8月29日(土) - 9月11日(金)

来訪場所: 理化学研究所和光キャンパス研究本館
春名純一

京都大学大学院情報学研究科特定研究員

期間: 2026年9月7日(月) - 11日(金)

来訪場所: 理化学研究所和光キャンパス研究本館

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