Search Event
668 results
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SeminarAI 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
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Lecture
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
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ColloquiumEfficient 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
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LectureiTHEMS-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
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ColloquiumHidden 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
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ColloquiumThe 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
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ColloquiumHow did we come to be? — Particle Physics for the Next Decades —
July 10 (Fri) 15:30 - 17:00, 2026
Hitoshi Murayama (Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo / Professor, Department of Physics, University of California, Berkeley, USA)
Particle Physics is a study of the smallest and the biggest to uncover the fundamental laws that govern the universe. In recent years, both the United States and Europe have been through long-range planning processes. The future plans worldwide include the studies of (1) neutrinos that may have saved us from a complete annihilation, (2) the Higgs boson that keeps us in one piece, (3) dark matter that assembled us from the primordial soup, (4) inflation that created the macroscopic universe, and (5) the exploration of unknown particles and forces. It requires development of mind-boggling technologies.
Venue: Okochi Hall (Main Venue) / via Zoom
Event Official Language: English
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SeminarThom polynomials relative to prescribed maps around the boundary
July 3 (Fri) 15:00 - 17:30, 2026
Masato Tanabe (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Thom polynomials are universal cohomological obstructions to the appearance of singularities of given types in differentiable maps. Introduced by R. Thom in the 1950s, they have been extensively studied ever since. In the first half of this talk, I would like to recall their theory with introduction of algebro-topological materials. In the second half, I would also like to talk about applications of Thom polynomials to topology of non-singular maps. Since this century, various invariants of immersions/embeddings have been expressed in terms of singularities of their extensions (a.k.a. singular Seifert surfaces). However, those formulas are obtained in different forms and remain somewhat scattered. As the first step to unify them, I would like to introduce Thom polynomials relative to prescribed maps around the boundary. As a main result, we show a structure theorem of Thom polynomials relative to framable immersions. In fact, most earlier formulas are summarized as the vanishing of "correction terms" appearing in the structure theorem. This is an advanced seminar for mathematical researchers.
Venue: Seminar Room #359, Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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SeminarCosmic-ray bath in a past supernova gives birth to Earth-like planets
July 3 (Fri) 14:00 - 15:15, 2026
Ryo Sawada (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
A key question in astronomy is how ubiquitous Earth-like rocky planets are. The formation of terrestrial planets in our Solar System was strongly influenced by the radioactive decay heat of short-lived radionuclides (SLRs), particularly 26 Al (aluminum-26), likely delivered from nearby supernovae. However, current models struggle to reproduce the abundance of SLRs inferred from meteorite analysis without destroying the protosolar disk. We propose the "immersion" mechanism, where cosmic-ray nucleosynthesis in a supernova shockwave reproduces estimated SLR abundances at a supernova distance (~1 parsec), preserving the disk. We estimate that solar mass stars in star clusters typically experience at least one such supernova within 1 parsec, supporting the feasibility of this scenario. This suggests that Solar System─like SLR abundances and terrestrial planet formation are more common than previously thought.
Venue: #424-426, Main Research Building
Event Official Language: English
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Seminar
Genome Structural Variation and the Evolutionary Potential of Sex in the Unicellular Green Alga Closterium
July 2 (Thu) 13:00 - 14:00, 2026
Yawako W. Kawaguchi (Postdoctoral Researcher, Molecular Life History Laboratory, National Institute of Genetics)
Genome size varies widely among eukaryotes, even between closely related species and within species. However, we still know relatively little about where such variation originates, how organisms tolerate its potential negative effects, and whether it can contribute to adaptation. In this seminar, I will present our studies on the unicellular green alga Closterium peracerosum–strigosum–littorale complex. I will first show that genome size variation in this alga is largely explained by extensive genome-wide copy number variation, and that gene expression can be buffered against changes in gene copy number. I will then show that a single episode of sexual reproduction can generate substantial variation in population growth rates under dual environmental stressors, with some F1 populations growing even when both parental strains decline. Finally, I will discuss how sexual reproduction may drive rapid evolutionary change not only by reshuffling alleles, but also by rearranging genome structure.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar TodayPrimitive Ideals and Hilbert Space Representations of Quantized Coordinate Algebras of Complex Semisimple Lie Groups
June 26 (Fri) 16:30 - 18:00, 2026
Heon Lee (Postdoc Researcher, Institute for Advanced Study in Mathematics, Harbin Institute of Technology, Republic of Korea)
The primitive ideals of the coordinate algebra $ \mathcal{O} ( G ) $ of a complex semisimple Lie group $ G $ are in bijection with the points of $ G $, via the correspondence assigning to each point of $ G $ the kernel of the associated evaluation homomorphism on $ \mathcal{O} ( G ) $. This establishes a direct link between the algebraic structure of $ \mathcal{O} ( G ) $ and the geometry of $ G $. In this talk, we investigate the quantum analogue of this classical relationship for the $ q $-deformation $ G_q $. Specifically, we establish a sharp dichotomy: primitive ideals in homogeneous Joseph strata arise as kernels of irreducible representations of $ \mathcal{O} ( G_q ) $ by bounded operators on Hilbert spaces, which provide a quantum analogue of evaluation homomorphisms at points of $ G $, whereas those in inhomogeneous Joseph strata do not. This clarifies the extent to which the primitive spectrum of $ \mathcal{O} ( G_q ) $ can be accessed through operator-theoretic methods. We also analyze the semiclassical consequences of this result in light of the fact that the primitive ideals of $ \mathcal{O} ( G_q ) $ are parametrized by the symplectic leaves of the natural Poisson structure on $ G $. This talk is based on joint work with Christian Voigt.
Venue: via Zoom / Seminar Room #359
Event Official Language: English
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Seminar
Fermionic modes of D-instanton wormholes from broken local supersymmetry
June 24 (Wed) 15:30 - 17:00, 2026
Hiroshi Itoyama (Specially Appointed Professor, Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka Metropolitan University)
In low-energy supergravity treatment of type IIB superstring on general D-instanton wormhole profiles in the bulk, we obtain non-vanishing scalar two-point functions in addition to the vanishing 〈τ＊τ＊〉 that corresponds to the BPS amplitude detected by two D-instantons at their respective boundaries. This is exploited to show that the modes of broken local supersymmetry in the bulk deliver the fermionic (diagonal) modes on the boundaries through the deformation by the form of current-current two point functions propagating on the tree level cylinder geometry. Our treatment is generalizable to multi D-instanton cases and general Euclidean branes.
Venue: #359, 3F, Main Research Building (Main Venue) / via Zoom
Event Official Language: English
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Seminar
iTHEMS Cosmology Forum n°6 - Cosmological Collider Physics
June 22 (Mon) 9:15 - 17:00, 2026
Yi Wang (Professor, Department of Physics, Hong Kong University of Science and Technology, Hong Kong)
Masahide Yamaguchi (Director, Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)
Kyohei Mukaida (Assistant Professor, Theory Center, High Energy Accelerator Research Organization (KEK))
Kazuyuki Akitsu (R&D, Proxima Technology)This sixth workshop will bring together researchers exploring the physics of the early universe through cosmological collider signatures. Primordial non-Gaussianities generated during inflation provide a unique opportunity to probe heavy particles and high-energy interactions in the early universe, potentially accessing energies much larger than that probed by terrestrial experiments. In recent years, the subject has developed rapidly, incorporating ideas from inflationary cosmology, quantum field theory in curved spacetime, effective field theory, and scattering amplitudes.
Venue: Okochi Hall
Event Official Language: English
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Seminar
The Virasoro TQFT approach to 3D gravity and the sum over topologies (QuIG Seminar)
June 19 (Fri) 13:30 - 16:00, 2026
Mengyang Zhang (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)
In the first part of this talk, I will review the construction of Virasoro TQFT from the Chern–Simons formulation of pure AdS_3 gravity and its application to the statistics of two-dimensional holographic CFT data. I will then discuss its extension to three-dimensional de Sitter gravity and its relation to the double-scaled SYK model. In the second part, I will address the issue of topological invariance in Virasoro TQFT. Despite being “topological,” its partition function is not well-defined on arbitrary three-manifolds, distinguishing it from conventional Reshetikhin–Turaev–Witten TQFTs. I will explain how far the standard proofs of topological invariance can be generalized to this framework. Finally, I will comment on the role of the sum over topologies in the 3D gravitational path integral.
Venue: via Zoom / #359, Main Research Building
Event Official Language: English
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Seminar
Improving data analysis in biology and in general with Tensor Decomposition
June 18 (Thu) 13:00 - 14:30, 2026
Lucas Sort (Postdoctoral Researcher, Mathematical Genomics RIKEN ECL Research Unit, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
This talk will provide an introduction to the basic principles of tensor decomposition methods, especially CANDECOMP/PARAFAC (CP) decomposition. I will explain how such methods can be used to extract meaningful and interpretable patterns from high-dimensional tensor-structured data, which commonly arises in biology, as well as in a broad range of other scientific domains. These patterns can then be used to gain a better understanding of the phenomena under study. I will also briefly discuss how tensor decomposition methods can be extended for various types of data, focusing in particular on how I have been trying to better model longitudinal data.
Venue: via Zoom / Seminar Room #359
Event Official Language: English
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Seminar
Which Cosmological EFTs Survive the UV? A first step from quantum consistency to late-time cosmology
June 15 (Mon) 10:00 - 11:30, 2026
Carlos Pastor-Marcos (Ph.D. Student, ITP, Heidelberg University, Germany)
EFTs for cosmology are one of our best tools to describe possible departures from GR in the Universe we observe. However, not every low-energy theory can arise from a consistent quantum theory at high energies. In this talk, I will discuss how this question can be addressed using asymptotic safety (AS), and how UV consistency can constrain the space of viable modified-gravity EFTs. Instead of treating all EFT parameters as equally possible, we can ask which regions of theory space are connected to a well-defined fixed point in the UV. This provides the first ingredients of a UV-to-IR strategy, restricting the allowed low-energy theories and indicating how quantum-gravity information may reach cosmology. I will first give a pedagogical introduction to AS and the functional RG, focusing on the physical picture rather than technical details. I will then apply the framework to generalized Proca theories, a class of vector–tensor modified-gravity EFTs with relevant cosmological applications, to illustrate how this analysis is performed in practice and how it can constrain viable IR theories. I will close by discussing how UV completion can become a practical guide for cosmology, translating quantum-consistency conditions into phenomenological signatures, from late-time modified gravity to early-universe observables, strong-gravity tests and GW probes.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Noncritical Conformal Gravity and 4D Liouville Theory
June 12 (Fri) 15:00 - 16:30, 2026
Nobuyoshi Ohta (Visiting Professor, Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka Metropolitan University)
We study the quantum aspects of the conformal gravity in four dimensions, specifically addressing a known discrepancy in beta functions between general quadratic curvature theories and conformal gravity, which corresponds to two scalar degrees of freedom. We demonstrate that this mismatch is resolved by carefully introducing gauge-fixing and ghost terms via the BRST symmetry, which effectively adds the two scalar modes. Drawing lessons from two-dimensional quantum gravity and Liouville theory, we proceed to integrate the four-dimensional trace anomaly to derive a consistent Liouville action, which is given by a free-field action for the conformal mode with a consistent conformal anomaly. We give the condition that the BRST transformation is anomaly free. Finally I would like to talk about some application of this theory.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Quantum Improved Black Holes in Asymptotically Safe Gravity
June 11 (Thu) 15:00 - 16:30, 2026
Chiang-Mei Chen (Professor, Department of Physics, National Central University, Taiwan)
In this talk, I will explore quantum-improved black hole solutions within the framework of asymptotic safety. In this approach, the Newton coupling becomes scale-dependent, necessitating a meaningful identification between the energy scale and a corresponding physical (length) scale to derive observable consequences for black hole spacetimes. I will argue that the requirement of consistency with the first law of black hole thermodynamics provides a physically motivated criterion for this scale-setting, particularly near the event horizon. Applying this principle, we propose a specific identification scheme that leads to a regularized geometry capable of resolving the ring singularity of Kerr black holes.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Mode Estimation in the Space of Phylogenetic Trees with Applications to Species Tree Reconstruction
June 11 (Thu) 13:00 - 14:00, 2026
Yuki Takazawa (Project Research Associate, Graduate School of Information Science and Technology, The University of Tokyo)
Analyzing samples of phylogenetic trees arises in many settings, including bootstrap tree sets, Bayesian posterior samples, and collections of gene trees. The Billera–Holmes–Vogtmann (BHV) tree space provides a geometric framework in which such samples can be viewed as point clouds in a common metric space. A fundamental summary in this space is the Fréchet mean, but it has a property known as stickiness: mean trees tend to lie on lower-dimensional boundaries of the space, corresponding to unresolved, non-binary trees. This behavior can be undesirable, as the mean may then fail to represent the center of interest. In this talk, I will introduce the BHV tree space framework and discuss mode estimation as an alternative way to summarize distributions of phylogenetic trees. After motivating the use of the mode, I will present simple approaches to mode estimation and discuss their consistency and robustness properties. I will then discuss how these ideas can be applied to species tree reconstruction from conflicting gene trees. To handle larger taxon sets, I will use quartet-based aggregation, in which local modal summaries are constructed from trees restricted to sets of four taxa and then combined to reconstruct a species tree. This approach provides a scalable way to apply mode estimation to trees with many taxa and helps reduce the influence of contamination in gene tree collections, as illustrated in simulation studies.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Disorder and Defects in Critical Systems
June 8 (Mon) 13:30 - 15:00, 2026
Baishali Roy (Postdoctoral Fellow, Indian Institute of Technology Kanpur, India)
Real critical systems are often constrained by boundaries and affected by impurities. In 3d, the effect of disordered impurities on the boundary can be modeled by a random magnetic field on a two-dimensional defect. In this talk, I will discuss how such disorder affects the Wilson-Fisher fixed point in d=4−\epsilon dimensions. By analyzing the one-loop RG flow of the defect couplings using the replica formalism, we find a non-trivial "dirty" fixed point which represents a new boundary universality class, stabilized by the bulk \phi^4 interaction. Disordered systems at critical points are known to exhibit logarithmic behavior — I will also discuss how operator mixing in the replica limit gives rise to a logarithmic defect CFT in our setup.
Venue: #359, 3F, Main Research Building (Main Venue) / via Zoom
Event Official Language: English