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

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A new math framework captures symmetry in layered materials

An international research team including Sonia Mahmoudi, Assistant Professor at the Advanced Institute for Materials Research (AIMR), Tohoku University, and Visiting Scientist at iTHEMS's Tohoku University Collaboration Team, has developed a new mathematical framework for describing symmetry in complex layered structures. The study extends orbifold notation, a compact symbolic language for describing symmetry, to structures that repeat in two directions while extending into three dimensions. Although this notation has been used for two-dimensional periodic patterns and three-dimensional structures that repeat in all directions, a corresponding framework for periodic layered structures had been unavailable. The researchers applied the framework to knitted fabrics, whose interlocking strands form three-dimensional structures. The work is expected to help clarify the relationship between structure and properties in layered and entangled materials, supporting the design of materials with desired characteristics. For more details, please refer to the related link.

2026-11-10
Developing a New Method to Uncover Hidden Topological Materials

A collaborative research team including Seishiro Ono, then a Special Postdoctoral Researcher at iTHEMS (now a Visiting Scientist at iTHEMS), has developed a theoretical method to systematically construct topological invariants, which are used to identify the topological properties of materials, according to crystal symmetry. The method uses the Atiyah-Hirzebruch spectral sequence, a mathematical technique for investigating the topological properties of the entire momentum space. When applied to time-reversal-symmetric superconductors that conventional symmetry indicators cannot diagnose, the method completely identified their topological properties in 159 of the 230 space groups. This result is expected to enable the theoretical discovery of topological materials that previous methods could not identify, accelerating comprehensive materials searches and the search for new materials. For more details, please refer to the related link.

2026-11-09
Proof of the Law of Increasing Entropy from Quantum Mechanics

A collaborative research group including Ryusuke Hamazaki, Senior Research Scientist at iTHEMS and RIKEN Hakubi Team Leader, has for the first time proved that the law of increasing entropy, a fundamental expression of the second law of thermodynamics, can be derived from quantum mechanics. The group constructed a quantum-mechanical framework for thermal equilibrium states and thermodynamic operations based on macroscopically meaningful physical quantities. Using this framework, they showed that entropy does not decrease under macroscopic operations on thermal equilibrium states, including pure quantum states. This result is expected to advance the understanding of how thermodynamics, the law governing the macroscopic world, emerges from quantum mechanics, the law governing the microscopic world. For more details, please refer to the related link.

2026-11-09
Farewell Message from Che-Yu Chen

Our colleague, Che-Yu Chen, will leave iTHEMS on November 30, 2026, and join the Institute for Basic Science (IBS) in South Korea as a Young Scientist Fellow. We will all miss him and wish him the best of luck in his new endeavor. Here is a message from Che-Yu: <i>Since joining iTHEMS in 2023, I have greatly benefited from its stimulating and exciting research environment. Through discussions with researchers from diverse backgrounds, I have been constantly inspired by how people from different fields can approach the same problem from different perspectives. At the same time, I have been fascinated by how often scientific questions arising in seemingly unrelated fields can be addressed using similar mathematical or physical approaches. This has been a truly unique and rewarding experience during my time at iTHEMS. In addition, I have had the opportunity to organize several workshops and intensive lectures, as well as attend numerous seminars. These experiences have been extremely fruitful and have significantly broadened my research horizons. </i> <i>My time at iTHEMS has also been particularly special to me personally, as I became the father of twins in 2024. I’m truly grateful to have been part of iTHEMS during such an important chapter of my life. It was an extremely challenging period for me, and I would like to express my heartfelt gratitude to all the assistants, especially Chikako-san and Keiko-san, for their kind support and patience in answering my endless questions. I am also deeply grateful to RIKEN for allowing me to take a couple of months of childcare leave overseas, an opportunity that, as far as I know, remains uncommon not only in Asia but also in many other parts of the world. Furthermore, I sincerely appreciate the freedom and flexibility that iTHEMS has given me to balance my research responsibilities with family life. </i> <i>Leaving Japan and joining IBS in South Korea marks the beginning of a new and challenging chapter in my life. Nevertheless, I will always cherish my time at iTHEMS, and I’m quite sure that I will return to visit from time to time!</i>

2026-11-09
Farewell message from Muzi Hong

Our colleague, Muzi Hong, left iTHEMS on October 11, 2026, and has joined Fermilab as a Research Associate. We all miss her and wish her the best of luck in her new endeavor. Here is a message from Muzi: <i>I had a wonderful time at iTHEMS. It was always a pleasure to discuss ideas with people from various fields and attend seminars on a wide range of topics. I enjoyed every Coffee Meeting. I also made many friends along the way. The secretaries were always kind and helpful. I would like to thank all my colleagues for creating such a friendly, welcoming, and professional environment at iTHEMS. I always look back on my time there with warmth and fond memories. I have now moved to Fermilab as a postdoc, but I will remain affiliated with iTHEMS as a visiting scientist. You are always welcome to visit me at Fermilab!</i>

2026-11-05
Reproducing Long-Term Variations in Venus's Atmospheric Superrotation

A joint research team including Takemasa Miyoshi, Team Director at the RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), has successfully reproduced long-term variations in the wind speeds of Venus's atmospheric "superrotation," a phenomenon characterized by extremely fast atmospheric circulation, using the Venus atmospheric data assimilation system ALEDAS-V. By incorporating wind observation data from the cloud tops collected by the Venus Climate Orbiter Akatsuki into numerical simulations, the team reproduced observed wind speed variations and differences between the northern and southern hemispheres. The researchers also estimated the three-dimensional structure of Venus's atmosphere, including altitudes where direct observations are unavailable. These findings demonstrate the potential of data assimilation techniques to reveal planetary atmospheric circulation patterns from limited observational data and are expected to contribute to future Venus exploration and planetary atmospheric research. For more details, please see the related links.

2026-10-30
Daisuke S. Shimamoto, Special Postdoctoral Researcher, Selected for the 59th (FY2026) Research Grant of the Ito Science Foundation

Daisuke S. Shimamoto, Special Postdoctoral Researcher in the Division of Fundamental Mathematical Science at the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), has been selected for funding under the 59th (FY2026) research grant program of the Ito Science Foundation. The program supports young researchers pursuing original basic research. This year, two projects each were selected in physics and biological sciences. Shimamoto’s project is titled “Degrees of Freedom and Constraints in Periodic Tangle Structures.” It focuses on structures formed by interwoven threads or interlinked rings, such as knitted fabrics and chain mail, and explores how these arrangements affect their susceptibility to damage and their shape. By combining mathematical and physical approaches, the research is expected to offer new insights into the mechanisms underlying these familiar structures. Congratulations, Daisuke!

2026-10-27
Are Supernovae Giant Cosmic Particle Accelerators? Exploring a PeVatron Candidate through Visible Light and Neutrinos

A collaborative research group including Ryo Sawada, a Special Postdoctoral Researcher at RIKEN iTHEMS, has theoretically shown that the Type Ibn supernova SN 2023uqf may act as a “PeVatron,” capable of accelerating particles to extremely high energies. By connecting the explosion environment inferred from visible-light observations with a high-energy neutrino event detected by IceCube, the study presents a new approach to investigating the origin of cosmic rays. For further details, please see the related link.

2026-10-27
Riccardo Muolo Receives the 2026 Complex Systems Society Emerging Award

Riccardo Muolo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN iTHEMS) has received the 2026 Emerging Award from the Complex Systems Society (CSS). The award was presented at the 2026 Conference on Complex Systems (CCS 2026), held in Binghamton, New York, USA, on October 9–16, 2026. The CSS Emerging Award recognizes promising early-career researchers who have made significant contributions to complex systems science within three years of completing their PhD. Riccardo was recognized for developing new mathematical tools to understand the complex interactions underlying collective dynamics, including synchronization, pattern formation, and self-organization, as well as for his contributions to scientific outreach and dissemination. This award highlights his contributions to the mathematical understanding of complex systems and the interdisciplinary nature of his research. Congratulations, Riccardo, on this wonderful achievement!

2026-10-23
AI and Symmetry Accelerate the Design of Sound-Absorbing Woven Materials

An international research team including Sonia Mahmoudi, Assistant Professor at the Advanced Institute for Materials Research (AIMR), Tohoku University, and Visiting Scientist at iTHEMS's Tohoku University Collaboration Team, has developed a method that uses AI and symmetry to make the design of sound-absorbing woven materials more efficient. The researchers organized manufacturable weave patterns according to symmetry and trained an AI model on a limited set of detailed simulations, enabling rapid evaluation of many candidates. Predicted sound-absorption performance agreed with independent simulations within 5%. The team plans to test selected 3D-woven prototypes experimentally. For details, please see the related links.

2026-10-20

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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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