Joint Seminar on Cosmology

July 13 (Mon) 9:00 - 18:00, 2026

Yukihiro Kanda (Project Researcher, Institute for Cosmic Ray Research (ICRR), The University of Tokyo)
Fumiya Okamatsu (Research Assistant, Department of Physics, College of Humanities and Sciences, Nihon University)
Fumiya Sano (Ph.D. Student, Institute of Science Tokyo)

The Joint Seminar is a collaborative seminar series organized by universities and research institutes in and around Tokyo. It is held once every one or two months, with the venue rotating among the participating institutions. At each meeting, we have around three talks and open, informal discussions. After the seminar, participants are also welcome to join an informal social gathering.

Venue: Okochi Hall

Event Official Language: English

Visual system and (social) behavior in zebrafish

July 16 (Thu) 13:00 - 14:00, 2026

Fumi Kubo (Team Director, Laboratory for Sensorimotor Integration, RIKEN Center for Brain Science (CBS))

Animals make decisions about their actions using sensory information from the external world. Our lab investigates how the brain processes visual information and generates appropriate behavior using the vertebrate model organism, zebrafish. Our research has uncovered the neural circuits required for processing optic flow, a visual cue that animals use to estimate their own motion. We employ a diverse range of techniques, including behavioral tracking, live imaging of neural activity, and molecular and genetic characterization of neuronal cell types. More recently, our research has focused on social behavior, in which groups of animals collectively generate behavioral decisions. In this seminar, I will present our recent work investigating behavioral contagion in zebrafish.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Artificial Intelligence in New Physics Electroweak Phase Transition Studies

July 16 (Thu) 15:00 - 16:00, 2026

Yang Zhang (Professor, Henan Normal University, China)

The study of electroweak phase transitions in BSM involves complex numerical calculations, large parameter spaces, and the integration of multiple computational tools. In this talk, I will review recent developments in applying artificial intelligence to new physics phase transition studies. First, I will discuss how machine learning methods can accelerate electroweak phase transition studies, including efficient evaluations of phase transition dynamics, such as bounce action calculations, and the exploration of detectable parameter regions for gravitational-wave searches. Then, I will introduce the emerging role of AI agents in scientific workflows, including automated model construction, effective potential generation, and parameter scans. These developments illustrate how AI can transform traditional computational pipelines and provide new possibilities for future high-energy physics research.

Venue: via Zoom

Event Official Language: English

Mathematical Application Research Team Meeting #17

July 17 (Fri) 10:30 - 11:45, 2026

Hugo Koubbi (Ph.D. Student, CEREMADE, Université Paris Dauphine, France)

Mathematical Application Research Team is delighted to welcome Hugo Koubbi from CEREMADE, Université Paris Dauphine, for an upcoming team meeting. We warmly invite everyone to join us.

Venue: via Zoom / #359, Seminar Room #359

Event Official Language: English

A first step towards Non-Archimedean Geometric Quantization

July 17 (Fri) 14:00 - 15:30, 2026

Keita Goto (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Calabi--Yau manifolds have long attracted interest from both mathematics and physics, particularly in the context of mirror symmetry, and form an important class of compact Kähler manifolds. A compact Kähler manifold is Calabi--Yau if and only if it admits a Ricci-flat Kähler metric, which we shall call a CY metric. Such a metric is highly analytic in nature, as it is given as the solution to a second-order PDE on the manifold, namely the complex Monge--Ampère equation. When the Calabi--Yau manifold is a complex projective variety, one algebraic approach to understanding this analytically defined CY metric is to approximate it by algebraically defined metrics called balanced metrics. This framework was initiated by Donaldson and is now known as geometric quantization. In this talk, following the spirit of this theory, we consider a non-Archimedean analogue of this approximation theory. More precisely, for a non-Archimedean analytic space associated with a maximally degenerating family of Calabi--Yau manifolds, we study the approximation of the NACY metric, a non-Archimedean analogue of the CY metric, by algebraically defined metrics. In particular, we introduce NA balanced metrics, which are expected to provide such an approximation, and explain that, for totally degenerating families of abelian varieties, NA balanced metrics indeed approximate the NACY metric.

Venue: Seminar Room #359, Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

The 33th MACS Colloquium

July 17 (Fri) 14:45 - 18:00, 2026

Hajime Naruse (Professor, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University)
Yohsuke Murase (Team Director, Mathematical Social Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

14:45-15:00 Teatime Discussion 15:00-16:00 Hajime Naruse (Professor, Department of Geophysics, Graduate School of Science, Kyoto University) "What Do Sedimentary Layers Remember? Exploring Past Earth Environments through Machine Learning" 16:15-17:15 Yosuke Murase (Team Director, Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN) "Mathematics of Cooperation in Society: The Evolution of Cooperation through Direct and Indirect Reciprocity" 17:15-18:00 Discussion

Venue: Science Seminar House (Map 9), Kyoto University

Event Official Language: Japanese

Entanglement suppression for ΩΩ scattering

July 17 (Fri) 15:00 - 16:30, 2026

Katsuyoshi Sone (Ph.D. Student, Graduate School of Science, Tokyo Metropolitan University)

The S-matrix describing the scattering process can be expressed in terms of projection operators onto the allowed spin–flavor channels and the corresponding phase shifts. Using the entanglement entropy in the spin space of the two-particle state, one can define the entanglement power, which quantifies the ability of the S-matrix to generate entanglement in the system. By investigating the conditions under which the entanglement power of the S-matrix is minimized, namely, the conditions for entanglement suppression, one can derive relations among the phase shifts in different spin–flavor channels. Furthermore, by comparing these relations with the interaction Lagrangian, one can identify the underlying symmetries [1,2]. In this work, we apply the entanglement suppression framework to two-baryon scattering involving spin-3/2 baryons in the flavor decuplet [3]. Lattice QCD calculations have shown that the spin-0 ΩΩ system exhibits scattering close to the unitary limit. Combining this result with the relation between the phase shifts obtained from entanglement suppression, we discuss the scattering behavior of the spin-2 ΩΩchannel.

Venue: #445-447, 4F, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Workshop on Discrete & Continuous Aspects of Reaction-Diffusion in Pattern Formation (DiCoRD2026)

July 22 (Wed) - 24 (Fri) 2026

Ryoko Oishi-Tomiyasu (Professor, Institute of Mathematics for Industry, Kyushu University)
Makoto Sato (Professor, Kanazawa University)
Nobuhiko Suematsu (Professor, School of Interdisciplinary Mathematical Sciences, Meiji University)
Yasumasa Nishiura (Professor Emeritus, Hokkaido University)
Riccardo Muolo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Jonathan Dawes (Professor, University of Bath, UK)
Henrik Weyer (Postdoctoral Scholar, University of California, Santa Barbara, USA)
Yuzuru Kato (Associate Professor, Department of Complex and Intelligent Systems, School of Systems Information Science, Future University-Hakodate)
Ayumi Ozawa (Young Research Fellow, Japan Agency for Marine-Earth Science and Technology (JAMSTEC))
Takanori Sugimoto (Associate Professor, Faculty of Engineering Science, Kansai University)
Natsuhiko Yoshinaga (Professor, School of Systems Information Science, Future University-Hakodate)
Jens Rademacher (Professor, University of Hamburg, Germany)
Takeshi Fukao (Professor, Faculty of Advanced Science and Technology, Ryukoku University)
Yoshitaro Tanaka (Associate Professor, School of Systems Information Science, Future University-Hakodate)
Shuji Ishihara (Project Associate Professor, The University of Tokyo)
Hiroshi Ishii (Assistant Professor, Research Institute for Electronic Science, Hokkaido University)
Takeshi Watanabe (Associate Professor, Nagano University)
Antoine Diez (Research Scientist, Mathematical Application Research Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Venue: via Zoom / Research Seminar Room 3, 6F, High-Rise Building, Meiji University (Nakano Campus)

Event Official Language: English

The decision intelligence of humans and machines

July 24 (Fri) 10:30 - 11:30, 2026

Petter Holme (Professor, Department of Computer Science, Aalto University, Finland)

The event has been rescheduled from July 22 to July 24. To understand our near-future of artificial intelligence firmly integrated into many levels of social life, a challenge is to understand the differences and similarities between human and AI decision-making. In controlled laboratory settings assessing risk and uncertainty, LLMs demonstrate superhuman efficiency but fundamentally diverge from human behavior through a rigid hyper-rationality and an inability to disengage from obsolete strategies. However, when applied to messy, real-world dilemmas "in the wild," these models pivot to function as highly effective "satisficers". Human subjects consistently prefer this artificial counsel over human peer advice, noting its ability to carefully balance emotional context with logical constraints while actively reducing anxiety and regret. Ultimately, this synthesis shows that while AI can offer near-optimal laboratory performance and therapeutic impact in daily life, they also have a distinct lack of behavioral plasticity that we need to account for in models of the future.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Unraveling the very early universe with black holes, boson stars, and cannibal stars

July 24 (Fri) 14:00 - 16:00, 2026

Takeshi Kobayashi (Associate Professor, International School for Advanced Studies (SISSA), Italy)

According to the standard picture of cosmology, the rich structure of our universe began to form roughly 50,000 years after the big bang. In this talk I will explore the possibility that cosmic structures could also have formed in the extremely early universe, within a fraction of a second after inflation. I will show how this early structure formation can give rise to compact objects, including exotic stars and primordial black holes. These relics provide powerful probes of the first instants of cosmic history, especially the reheating epoch, and may even act as seeds for cosmological phase transitions. Note: This seminar is jointly organized by the iTHEMS-phys Study Group and the iTHEMS-ABBL Joint Astro Study Group.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Some instances where topological illustration induced new mathematics

July 24 (Fri) 16:30 - 18:00, 2026

Sofia Lambropoulou (Professor, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Greece)

We shall present instances from generalized knot theory, braid theory and their interactions, where illustration promoted understanding and inspired new mathematics. The first instance addresses a question of V.F.R. Jones whether one can make analogous constructions to the (2-variable) Jones polynomial using other braid groups and other types of Hecke algebras. The second instance addresses the question of formulating braid equivalences, analogous to the Markov theorem for classical braids, in settings where we may not even have available algebraic structures for the related braids. The third instance is about the theory of bonded knots and bonded knotoids used for modelling proteins.

Venue: via Zoom / Seminar Room #359, Seminar Room #359

Event Official Language: English

Center-vortex condensation and monopole condensation in 4d gapped phases

July 27 (Mon) 14:00 - 15:30, 2026

Yui Hayashi (JSPS Postdoctoral Research Fellow, Yukawa Institute for Theoretical Physics, Kyoto University)

Two well-known scenarios for quark confinement are center-vortex proliferation and monopole condensation. We consider gauge-invariant criteria for center-vortex condensation and monopole condensation in terms of Z(N) 1-form symmetry. The condensation of a soliton can be characterized by the non-suppression of the partition function with a proper twisted boundary condition, and we utilize this idea for these criteria. With these definitions, we show that gapped phases with the center-vortex condensation necessarily exhibit the monopole condensation.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

An optimal transport and information geometric framework for infinite-dimensional Gaussian measures and Gaussian processes (I)

July 28 (Tue) 13:30 - 14:45, 2026

Minh Ha Quang (Senior Research Scientist, Imperfect Information Learning Team, RIKEN Center for Advanced Intelligence Project (AIP))

Optimal transport (OT) and information geometry (IG) have been attracting much research attention in various fields, in particular machine learning and statistics. In this lecture, we present results on the generalization of IG and OT distances for finite-dimensional Gaussian measures to the setting of infinite-dimensional Gaussian measures and Gaussian processes. Our focus is on the Entropic Regularization of the 2-Wasserstein distance and the generalization of the Fisher-Rao Riemannian metric and related quantities. In both settings, regularization leads to many desirable theoretical properties, including in particular dimension-independent convergence and sample complexity. The mathematical formulation involves the interplay of IG and OT with Gaussian processes and the methodology of reproducing kernel Hilbert spaces (RKHS). All of the presented formulations admit closed form expressions that can be efficiently computed and applied practically. The mathematical formulations will be illustrated with numerical experiments on Gaussian processes.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

An optimal transport and information geometric framework for infinite-dimensional Gaussian measures and Gaussian processes (II)

July 28 (Tue) 15:00 - 16:15, 2026

Minh Ha Quang (Senior Research Scientist, Imperfect Information Learning Team, RIKEN Center for Advanced Intelligence Project (AIP))

Divergences between probability distributions play a crucial role in many areas of probability theory, statistics, machine learning, and their applications. While a large part of the literature is focused on divergences between finite-dimensional distributions, there is a growing body of work on infinite-dimensional distances/divergences, which are motivated by applications in functional data analysis, Bayesian inverse problems, and functional Bayesian neural networks, among others. In this lecture, we present an overview of recent results on some of the most important divergences being studied, including the Kullback-Leibler, Renyi, and Geometric Jensen-Shannon divergences. We discuss the many challenges that arise in the infinite-dimensional setting, e.g. the lack of a natural reference measure such as the Lebesgue measure and the fact that many functions such as determinants and logarithm are only well-defined in specific settings. In particular, in the setting of Gaussian measures on infinite-dimensional Hilbert spaces, the closed form expressions for the above divergences are only generalizable to equivalent Gaussian measures. We present the resolution to the above challenges via the geometrical framework of positive definite unitized (or regularized) trace class and Hilbert-Schmidt operators, including the Alpha and Alpha-Beta Log-Determinant divergences. Using this framework and the methodology of reproducing kernel Hilbert spaces (RKHS), we furthermore obtain consistent finite-dimensional  approximations of the above divergences in the Gaussian process setting, with dimensional-independent sample complexities. The resulting numerical algorithms can be readily employed in practical applications. We shall also discuss the generalization of the above classical divergences above to the quantum setting, namely the Quantum Jensen-Shannon divergence between quantum states, defined in terms of the von Neumann and Tsallis entropies, from finite to infinite-dimensional settings.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Quantum Reference Frames for Quantum Gravity

July 30 (Thu) 14:00 - 16:00, 2026

Luca Marchetti (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU))

This seminar is the first part of a two-part mini-seminar series organized by the Quantum Gravity Gatherings study group. It is intended to have a more lecture-style format, with an extended duration of up to two hours. This will allow the speaker sufficient time to introduce the framework in a clear and pedagogical manner, while also leaving ample room for questions and discussion with the audience. Title: Quantum Reference Frames for Quantum Gravity Abstract: Internal quantum reference frames provide a general framework for handling symmetries in quantum theory, with applications ranging from quantum gravity and gauge theories to quantum information and foundational physics. I will first introduce the formalism in simple mechanical systems, before turning to classical gravity. There, I will motivate the need for internal, dynamical frames in background-independent theories to define relationally local gauge-invariant observables, and show how this framework leads to a relational update of general covariance: frame covariance. I will then move to non-perturbative quantum gravity, showing how quantum reference frames can be used to define a manifestly gauge-invariant relational path integral, which is also invariant under transformations between quantum reference frames. It therefore provides a perspective-neutral description of quantum gravitational physics. I will also discuss the associated relational effective actions. Although effective actions are, in general, not frame-covariant off shell, the on-shell physics they encode is. Finally, I will present several physical consequences of this framework, including the fuzziness of frame-changed local correlators, the non-trivial interplay between quantum-reference-frame transformations and time evolution, and the frame-dependence properties of ground sectors and Hartle-Hawking prescriptions. I will conclude by outlining future directions, with particular emphasis on a relational notion of the renormalization group flow.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

Loop expansion in polymer field theory: application to phase separation

July 30 (Thu) 16:00 - 17:00, 2026

Kiyoharu Kawana (Research Fellow, Korea Institute for Advanced Study (KIAS), Republic of Korea)

Liquid-liquid phase separation underlies phenomena ranging from protein condensate formation to the phase coexistence of synthetic polymers. In this talk, we develop a field theoretic loop expansion in homopolymer systems by identifying the inverse polymer density ρ^{-1} as the Planck constant ℏ in quantum field theory. The 1-loop approximation is known as the random phase approximation (RPA) and has been extensively applied to many (hetero)polymer systems. We calculate the leading-order (2-loop) and next-to-leading-order (3-loop) corrections to the RPA free energy, denoted as RPA+ and RPA++, respectively. Testing the binodal predicted by the RPA+ against molecular dynamics simulations of bead-spring chains with Gaussian pair interactions, we find that the RPA+ qualitatively improves the dilute-phase coexistence density over the RPA, while the critical point error remains comparable to that of the RPA. Our results establish the loop expansion as a systematic route for refining the RPA-based binodal predictions for polymer phase separation. This talk is based on arXiv: 2605.01261.

Venue: via Zoom

Event Official Language: English

Quantum Gravity and Emergent Cosmology: A Group Field Theory Perspective

July 31 (Fri) 14:00 - 16:00, 2026

Luca Marchetti (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU))

This seminar is the second part of a two-part mini-seminar series organized by the Quantum Gravity Gatherings study group. It is intended to have a more lecture-style format, with an extended duration of up to two hours. This will allow the speaker sufficient time to introduce the framework in a clear and pedagogical manner, while also leaving ample room for questions and discussion with the audience. Title: Quantum Gravity and Emergent Cosmology: A Group Field Theory Perspective Abstract: I will introduce the Group Field Theory (GFT) approach to quantum gravity, emphasizing its connections with matrix and tensor models, discrete gravity path integrals, and loop quantum gravity. Through these connections, GFTs emerge naturally as quantum field theories of "spacetime atoms". I will then discuss how semiclassical, macroscopic physics can emerge from GFT, touching upon the challenges of defining locality and coarse-graining in quantum gravity, and on how these can be naturally addressed within relational frameworks. I will present a concrete implementation of this relational strategy in GFT and show how a simple relational coarse-graining scheme can be used to extract cosmological physics. Within the resulting cosmological models, the initial singularity is resolved into a quantum bounce, while cosmological perturbations emerge from the quantum entanglement of the underlying quantum-gravity degrees of freedom, with effective dynamics modified on trans-Planckian scales. Finally, I will show that quantum-gravitational interactions alone can generate cosmic acceleration, leading both to dynamical dark energy and to a slow-roll inflationary phase. I will conclude by showing recent observational constraints on such emergent dynamical dark energy models, and by providing an outlook on future research directions.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building

Event Official Language: English

How Reputation Sustains Cooperation: Mathematical Theories of Indirect Reciprocity

August 6 (Thu) 15:00 - 16:00, 2026

Yohsuke Murase (Team Director, Mathematical Social Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Cooperation among unrelated individuals is a central puzzle in the evolution of social behavior. Indirect reciprocity offers one influential explanation: people help others not only because they expect direct returns, but also because their actions affect their reputation. In this seminar, I will review mathematical theories of indirect reciprocity, focusing on how reputation and social norms can sustain cooperation. I will begin with the classical framework of public assessment, where everyone shares the same view of each individual’s reputation, including the seminal work of Ohtsuki and Iwasa on the “leading eight” social norms. I will then turn to private assessment, where individuals may disagree about others’ reputations, and discuss why synchronization of opinions becomes essential for cooperation. Overall, the seminar aims to provide an accessible overview of how mathematical models allow us to formalize moral judgments—what counts as good or bad behavior—and to understand the evolution of cooperation through reputation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Genome Language Models: From DNA Sequences to Biological Foundation Models

August 13 (Thu) 15:00 - 16:00, 2026

Minrui Chen (Ph.D. Student, Kyushu University)

Recent advances in protein language models have greatly transformed protein structure prediction, functional annotation, and biomolecular design. In contrast, genome language models aim to learn directly from DNA sequences, which represent a more upstream layer of biological information encoding genes, regulatory logic, variant effects, and evolutionary signals. In this talk, I will introduce the basic motivation and recent progress of DNA and genome language models, including DNABERT, DNABERT-2, HyenaDNA, Evo, Evo 2, and AlphaGenome. I will discuss how different model architectures and tokenization strategies address the challenges of genomic sequence modeling, such as long-range dependencies, multi-scale biological structure, and genome-scale context.

Venue: #359, 3F, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Hidden Networks: From Phase Reductions to Effective Network Interactions

August 24 (Mon) 15:30 - 17:00, 2026

Christian Bick (Associate Professor, Department of Mathematics, Vrije Universiteit Amsterdam, Netherlands)

From networks of interconnected neurons in the brain to coupled electrochemical reactions: The collective dynamics of interacting dynamical systems shape the function (or dysfunction) of many systems that are critical for our everyday lives. For coupled oscillatory processes, synchronization is a prime example of emergent collective dynamics. But how oscillators interact is not necessarily obvious from (physical) connections between the oscillators. Here we look at phase reductions as a way to uncover the hidden 'effective' network interactions for coupled oscillators dynamics. On the one hand, these give insight into when oscillators do and do not interact (despite a link). On the other hand, they elucidate when and how nonpairwise higher-order interactions shape synchronization phenomena in coupled oscillator networks.

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

AI for Science Summer School

August 25 (Tue) - 27 (Thu) 2026

Masato Taki (Associate Professor, Graduate School of Artificial Intelligence and Science, Rikkyo University)
Lingxiao Wang (Deputy Team Director, AI as Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Vinicius Massami Mikuni (Associate Professor, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)
Naoya Takeishi (Lecturer, The Research Center for Advanced Science and Technology, The University of Tokyo)
Conglong Li (Senior Research Scientist, Google DeepMind, UK)
Akinori Tanaka (Senior Research Scientist, RIKEN Center for Advanced Intelligence Project (AIP))

Summer school for modern AI methods and their applications in scientific discovery. We want to answer the questions in AI for Science, Why do you need AI for your research? Which AI is most suitable for your needs? How can you use AI properly for your task? The school will cover both lectures and hands-on coding sessions, with topics including machine learning basics, generative models, Bayesian and simulation-based inference, foundation models and LLM agents. The problems include, experiment-to-phenomenology (inference and prediction), computation (generation), theory (auto-workflow and Co-Scientist), etc.

Venue: #345-347, Main Research Building, RIKEN Wako Campus (Main Venue) / via Zoom

Event Official Language: English

iTHEMS-UTokyo Intensive Lectures on Quantum Gravity

August 31 (Mon) - September 2 (Wed) 2026

Hikaru Kawai (Visiting Professor, Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka Metropolitan University)

iTHEMS-UTokyo Intensive Lectures on Quantum Gravity (10th Quantum Gravity Gatherings Lecture Series) The 10th QGG Lecture Series is a special three-day installment of the intensive lecture series organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS. This celebratory edition will feature Professor Hikaru Kawai from Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), who will deliver a series of lectures on themes related to quantum gravity. This lecture series will follow a style similar to Prof. Kawai's first QGG lectures, held three years ago at RIKEN (Wako) as the inaugural QGG event, which explored fundamental questions in quantum gravity, string theory, and the quantum universe. A distinctive feature of this 10th installment is that it will take place on the Komaba campus of The University of Tokyo, where one of the iTHEMS satellite offices is located. This will be the first QGG lecture series held outside Wako, with the aim of making the event more accessible to a broader group of participants. Format: Lectures will be given mainly in blackboard style and in English, encouraging active participation and in-depth Q&A discussions. Poster sessions will also be held, giving participants an opportunity to present their own work or topics of interest. These sessions are intended to foster communication and stimulate the exchange of ideas among participants. This event will take place in person only. Target audience: Senior scholars, early-career researchers, and students are all warmly welcome. Registration deadline: July 31, 2026

Venue: 21 Komaba Center for Educational Excellence (21 KOMCEE) East Building, Room K214, Komaba Campus, The University of Tokyo

Event Official Language: English

Efficient iBF: Balanced Integration of Fragmented Matching Markets for Welfare Improvement

September 4 (Fri) 15:30 - 17:00, 2026

Fuhito Kojima (Professor, Department of Economics, The University of Tokyo)

Matching markets often suffer from fragmentation, which leads to inefficiency. We model a fragmented market in a school-choice context and offer a practically relevant method for integration. Specifically, each student and school belong to a region, and we allow for inter-regional transfer of students with "balancedness" constraint: a matching is said to be balanced if, for each region, the outflow of students from that region to other regions is equal to the inflow of students from the latter to the former. Using a directed bipartite graph defined on students and schools, we characterize the set of Pareto efficient matchings among those that are individually rational, balanced and fair (efficient iBF). We also provide a class of polynomial-time algorithms to compute such matchings. When each region favors local students in their priority, the outcome of an algorithm from this class weakly improves student welfare upon the outcome where each region independently uses the deferred acceptance mechanism. Various real-life examples of fragmentation are discussed, and we illustrate how our method would address the issue.

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

The 11th Intensive Lectures on Quantum Gravity

September 7 (Mon) - 9 (Wed) 2026

Yasuyuki Hatsuda (Associate Professor, Department of Physics, Faculty of Science, Rikkyo University)

In the 11th event of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, we will have Prof. Yasuyuki Hatsuda from Rikkyo University, who will deliver a three-day lecture series on the analytic methods in black hole perturbation theory. Black hole perturbation theory plays a very important role in the developments of modern physics. For instance, in gravitational wave astronomy, it can describe the ringdown phase during the merger events of binary black holes. As the frequency and decay rate of each quasinormal mode are unique to the remnant black hole, one can test extreme-gravity physics by extracting those modes from the ringdown signal. In addition, the computation of black hole quasinormal modes based on black hole perturbation theory has relations connecting to conformal field theories and even to the computations of tidal Love numbers. With the broad applications, we expect this lecture series to provide fresh perspectives to researchers across a wide range of fields and to inspire new directions in their own research. The lectures will be delivered in a blackboard-style format (in English), designed to foster interaction, active participation, and in-depth Q&A discussions. In addition, short talk sessions will be held, giving participants the opportunity to present briefly on topics of their choice. Through this informal and dynamic setting, we hope to spark active interactions among participants and create an environment where ideas can be shared openly and enthusiastically. This event will take place in person only. Target audience: Senior scholars, early-career researchers, and students are all warmly welcome. Registration deadline: July 31, 2026

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Majorana Modes: Fundamentals, Status & Directions

October 13 (Tue) - 16 (Fri) 2026

Workshop Overview Majorana modes lie at the heart of contemporary condensed-matter physics, exhibiting non-Abelian exchange statistics; when protected by topology, they are robust against environmental perturbations. Here, “Majorana mode” is used broadly to include a localized zero-energy Majorana state (a Majorana zero mode) and chiral Majorana edge states with gapless dispersion crossing zero energy. This three-day in-person workshop returns to fundamentals and open questions. It opens with a tutorial session on the afternoon of October 13 for non-experts and adjacent fields, and emphasizes rigorous theory–experiment dialogue, robust methodology, and concrete benchmarks for realizing and testing Majorana modes. Participants Experimentalists and theorists working on Majorana modes Researchers in adjacent fields (quantum materials, superconductivity, mesoscopic physics) Graduate students and postdocs interested in entering the field Topics include (non-exhaustive) Majorana zero modes in a variety of nanostructures Chiral Majorana edge states in quantum spin liquids and other platforms Disorder, interactions, and realistic device modeling Experimental diagnostics and “smoking gun” signatures Topological Quantum Spin Systems

Venue: Okochi Hall

Event Official Language: English

AI and Scientific Discovery

October 19 (Mon) 14:00 - 15:30, 2026

Joseph Ledsam (Google Health Lead, Japan, Google Japan)

Artificial intelligence is having a transformative impact on health and scientific discovery. This presentation will trace the evolution from foundational breakthroughs to the sophisticated capabilities of today's large-scale AI models. It will explore how these advanced systems are creating new possibilities across the healthcare landscape, from accelerating therapeutic development to enhancing diagnostic processes and interpreting complex medical data. The session will also take a deeper look at the future possibilities for AI in health and explore the emerging role of agentic AI in scientific discovery. The core theme is the responsible development of AI to create tools that assist scientists, support healthcare professionals, and empower users. Bio: Dr Joseph Ledsam leads Google Health in Japan, where he works across AI research, digital health and health in Google products. He has led research in medical AI, genomics and drug discovery published in journals including Nature, Nature Medicine and Nature Methods. Before moving to Japan he worked as a medical doctor in the UK, and founded the Health Research and Genomics teams in Google DeepMind. He obtained his medical degree from The University of Leeds, UK, and was a research fellow at University College London during his clinical residency.

Venue: #435-437, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

KEK(-iTHEMS) Theory Workshop 2026

November 25 (Wed) - 27 (Fri) 2026

Hirotaka Hayashi (Professor, Department of Physics, School of Science, Tokai University)
Hikaru Kawai (Visiting Professor, Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka Metropolitan University)
Takato Mori (Ph.D. Student, Department of Particle and Nuclear Physics, School of High Energy Accelerator Science, The Graduate University for Advanced Studies (SOKENDAI))
Masaya Nakagawa (Assistant Professor, Department of Physics, Graduate School of Science, The University of Tokyo)
Masaki Shigemori (Professor, Department of Physics, Graduate School of Science, Nagoya University)
Tadashi Takayanagi (Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
Norihiro Tanahashi (Program-Specific Associate Professor, Department of physics, Graduate School of Science, Kyoto University)
Tatsuya Yamaoka (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Osaka)

The KEK Theory Workshop is an annual workshop on string theory and quantum field theory. Since 2014, it has been held every winter as an international workshop and has become one of the major annual events in the high-energy physics community in Japan. This year’s workshop will be held on site at the KEK Tsukuba Campus from November 25 to 27, and it will be jointly organized with RIKEN iTHEMS. The workshop this year aims to provide a forum for extensive discussions on recent developments in string theory, matrix models, gauge/gravity duality, black-hole microstates, lattice constructions of chiral gauge theories, and open quantum systems.

Venue: Seminar Hall, Building 3, KEK Tsukuba Campus

Event Official Language: English