Full exceptional collections on Fano threefolds and the braid group action

December 5 (Fri) 16:00 - 17:30, 2025

Anya Nordskova (Postdoctoral researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU))

The bounded derived category D^b(X) of coherent sheaves on an algebraic variety X is a powerful tool that encodes a wealth of information about X. In some cases D^b(X) admits a particularly nice description via so-called full exceptional collections, which allow one to view D^b(X) as being glued from the simplest building blocks, each equivalent to the derived category D^b(pt) of a point. In this situation the set of all full exceptional collections admits an action of the braid group. In 1993, Bondal and Polishchuk conjectured that this braid group action is always transitive. After a short historical overview I will sketch the idea behind the proof of Bondal-Polishchuk's conjecture in the case when X is a Fano threefold of Picard rank 1 (e.g. the projective space P^3). This is the first 3-dimensional case where the transitivity of the braid group action has been verified. The talk is based on joint work with Michel Van den Bergh.

Venue: 3F 345-347 Seminar Room, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

About analytic continuation of quantum field theories in non-integer dimensions

December 5 (Fri) 14:00 - 15:30, 2025

Slava Rychkov (Professor, Institut des hautes études scientifiques, France)

Analytic continuation in dimension has been used first as a way to regularize perturbative quantum field theory. But since the work of Wilson and Fisher, quantum field theory in d-dimension has been used more radically, to connect theories living say, in d=4, to theories in d=3 and d=2. Mathematically it's not fully clear what this means. I will give some thoughts about this subject, and I will describe some recent paradoxes which arise when one consider expansion of O(N) models around d=2, based on recent work with Fabiana De Cesare.

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

Event Official Language: English

The Functional Renormalisation Group: From the physics of strongly correlated systems to generative models

December 5 (Fri) 10:30 - 12:00, 2025

Jan Martin Pawlowski (Professor, Institute for Theoretical Physics, University of Heidelberg, Germany)

In the past decades, the functional renormalisation group (fRG) has matured into a comprehensive approach to strongly-correlated (non-perturbative) systems, covering quantitatively both universal and non-universal phenomena. The fRG also constitutes an ideal approach for unravelling structural aspects of quantum field theories. This is not only interesting for studies in mathematical physics, but also guides systematic diagrammatic expansion schemes. It is also used to set up novel statistical (lattice) approaches to non-perturbative phenomena. In the present talk I survey these advances and illustrate the progress with selected examples ranging from ultracold atoms, QCD and quantum gravity to novel generative architectures for lattice simulations and beyond.

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

Event Official Language: English

Quantum Information in Scattering: From Amplitude Poles to Entanglement Features

December 4 (Thu) 14:00 - 16:00, 2025

Chon Man Sou (Postdoctoral Researcher, Department of Physics, Tsinghua University, Beijing, China)

Probing quantum entanglement in high-energy collisions has recently become a rapidly growing direction in particle physics, aiming to measure quantum correlations at the highest energy scales accessible to humans. A key question is how such entanglement relies on the analytic structure of scattering amplitudes. In this talk, I will show that the pole structure, associated with intermediate heavy particles, leads to distinctive entanglement features. When a heavy particle mediates inelastic scatterings with three or more final particles, the entanglement entropy between its decay products and the rest exhibits a universal dip as the energy increases, reflecting the limited information flow through on-shell heavy particles and signaling entanglement suppression in the heavy-particle-dominated regime. This reveals entanglement structures beyond the usual “area-law” behavior of 2-to-2 processes. Finally, I will comment on possible ways to probe these features experimentally through analyses of final-state phase-space distributions. This talk is based on JHEP 10 (2025) 003 [arXiv: 2507.03555].

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

Event Official Language: English

Biological Background of Duplicated Sequence Evolution: A Focus on Gene Conversion

December 4 (Thu) 13:00 - 14:00, 2025

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

Duplicated sequences—such as gene families, tandem arrays, and segmental duplications—are common in many genomes. Their evolution is shaped by several biological processes, including mutation, recombination, duplication, deletion, and gene conversion. Among these, gene conversion is especially important because it can make nearby copies more similar, while leaving distant copies free to diverge. In this seminar, I will give a broad and accessible overview of the biological background related to duplicated sequences, with a particular focus on what is known about gene conversion. I will summarize well-established patterns such as its dependence on genomic distance, sequence similarity, and recombination context. These biological features are often studied separately, so organizing them in one place can help provide a clearer foundation. The goal of the talk is to outline the biological principles that motivate thinking about duplicated sequences in a more formal or quantitative way in the future. I will not discuss specific model details. Instead, this presentation will serve as background preparation for later theoretical work.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Spectral Network and Betti Lagrangians

December 3 (Wed) 14:00 - 16:00, 2025

Yoonjae Nho (General Welfare Assistant, Seongdong District Office, Republic of Korea)

In this talk I will discuss the interface of spectral network theory and real contact and symplectic topology. For the first hour, I will give an introduction to spectral network theory using the Berk-Nevins-Roberts example, and review symplectic topology. For the second hour, I will talk about how GMN (Gaiotto-Moore-Neitzke) network theory can be interpreted from a symplectic perspective. I will then give an introduction to weave theory, which allows one to construct certain Lagrangian generalizations of spectral curves. I will then explain how to combinatorially compute spectral networks, with some applications. This is based on joint work with Roger Casals [1].

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

Event Official Language: English

Quantum Computing Journal Club #1

December 2 (Tue) 10:00 - 12:00, 2025

Bring a recent paper on quantum computing for discussion. No need to prepare slides.

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

Event Official Language: English

The 30th MACS Colloquium

November 28 (Fri) 14:45 - 18:00, 2025

Isao Ishikawa (Program-Specific Associate Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University)
Ken-ichi Kurotani (Associate Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University)

14:45-15:00 Teatime discussion 15:00–16:00 Talk by Dr. Isao Ishikawa (Program-Specific Associate Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University) 16:15–17:15 Talk by Dr. Ken-ichi Kurotani (Associate Professor, Center for Science Adventure and Collaborative Research Advancement (SACRA), Graduate School of Science, Kyoto University) 17:15-18:00 Discussion

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

Event Official Language: Japanese

From phase reduction to hypergraphs: the higher-order dynamics of coupled phase oscillators

November 27 (Thu) 13:00 - 14:00, 2025

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

Networks are powerful tools in the modeling of complex systems, but they do not always capture the right interactions when multiple units are involved simultaneously. Such many-body interactions are encoded by higher-order structures which can be thought as extensions of networks. Over the last years, higher-order networks have been the focus of great excitement, since this novel framework has enormous potential for applications. In this talk, I will give an overview of higher-order interactions and their effects on nonlinear dynamics. I will introduce the basics of dynamics on networks and its extension to the case of higher-order interactions. As examples of the effects on nonlinear dynamics, I will discuss the case of phase reduction for systems with higher-order interactions and show the effects on synchronization dynamics.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Introduction to Game Theory #3

November 27 (Thu) 11:00 - 12:00, 2025

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

An introductory lecture on game theory to promote potential interdisciplinary collaborations. No prior knowledge is required — the lecture is intended for non-experts. We will cover the fundamental concepts to help you build an intuitive understanding of how game theory analyzes strategic interactions. After briefly reviewing the previous lectures, we will talk about repeated games, where players are engaged in games repeatedly.

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

Event Official Language: English

Hamiltonian Learning and Dynamics Prediction via Machine Learning

November 26 (Wed) 15:00 - 16:00, 2025

Li Keren (Assistant Professor, College of Physics and Optoelectronic Engineering, Shenzhen University, China)

Accurate prediction of quantum Hamiltonian dynamics and identification of Hamiltonian parameters are crucial for advancements in quantum simulations, error correction, and control protocols. This talk introduces a machine learning model with dual capabilities: it can deduce time-dependent Hamiltonian parameters from observed changes in local observables within quantum many-body systems, and it can predict the evolution of these observables based on Hamiltonian parameters. The model’s validity was confirmed through theoretical simulations across various scenarios and further validated by two experiments. Initially, the model was applied to a Nuclear Magnetic Resonance quantum computer, where it accurately predicted the dynamics of local observables. The model was then tested on a superconducting quantum computer with initially unknown Hamiltonian parameters, successfully inferring them. We believe that machine learning techniques hold great promise for enhancing a wide range of quantum computing tasks, including parameter estimation, noise characterization, feedback control, and quantum control optimization.

Venue: via Zoom

Event Official Language: English

Adaptive navigation strategies in adversarial predator-prey contexts

November 20 (Thu) 13:00 - 14:00, 2025

Nozomi Nishiumi (Specially Appointed Associate Professor, Academic Assembly Institute of Science and Technology, Niigata University)

Animal navigation has long been a central topic in behavioral biology. In predator-prey systems, both predators and prey must navigate strategically - predators to capture prey and prey to reach safety - each evolving to outsmart the other through coevolution. To uncover the essence of these navigation strategies, I have investigated behavioral mechanisms across taxa. In bats, my collaborators and I found that they integrate multiple sensory and flight tactics to keep erratically flying moths within detection range. In pigeons, we discovered that individuals anticipating drone attacks adjust their positions toward the rear within the flock. I will also introduce an experimental framework that enables controlled interactions between real animals and virtual agents driven by reactive motion control, allowing quantitative tests of navigation efficiency. Through this seminar, I aim to highlight how studies of predator-prey navigation can bridge biology and engineering, providing insights into adaptive decision-making in dynamic environments.

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

Event Official Language: English

9th QGG Intensive Lectures – Correlation Effects in Quantum Many-Body Systems: Some Prototypical Examples in Condensed Matter Physics

November 19 (Wed) - 20 (Thu) 2025

Norio Kawakami (Deputy Director, Fundamental Quantum Science Program, TRIP Headquarters, RIKEN)

The ninth installment of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, will feature Prof. Norio Kawakami from the Fundamental Quantum Science Program (FQSP) under RIKEN's Transformative Research Innovative Platform (TRIP). Over the course of two days, Prof. Kawakami will deliver a lecture series on quantum many-body systems. In recent years, insights from quantum many-body physics have become central to research in quantum gravity, where correlation effects induced by gravity play nontrivial roles. By bridging perspectives from gravitational physics and quantum many-body dynamics, one hopes to understand how macroscopic spacetime and its geometric properties emerge from the collective behavior of quantum constituents at microscopic scales. In this lecture series, Prof. Kawakami will introduce the fundamental properties of correlation effects through representative examples in condensed matter physics. A distinctive aspect of this event is its joint organization with the Fundamental Quantum Science Program (FQSP) at RIKEN. The goal is to further strengthen connections between the quantum gravity, condensed matter, and quantum information communities. 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. Abstract: Some examples of theoretical methods to treat strongly correlated systems in condensed matter physics are explained. We start with the Kondo effect, which is one of the most fundamental quantum many-body problems and has been intensively studied to date in a wide variety of topics such as dilute magnetic alloys, heavy fermion systems, quantum dot systems, etc. Dynamical mean-field theory (DMFT) is then introduced, which enables us to systematically treat strongly correlated materials such as a Mott insulator. It is shown that the essence of DMFT is closely related to the Kondo effect. Furthermore, we explain how to apply conformal field theory (CFT) to treat correlation effects in one-dimensional electron systems.

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

Event Official Language: English

Chiral anomaly in Hamiltonian lattice gauge theory

November 18 (Tue) 10:00 - 12:00, 2025

Arata Yamamoto (Senior Research Scientist, Quantum Mathematical Science Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

The 4th quantum computing gathering organized by Quantum Computing Study Group

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

Event Official Language: English

Mathematical Application Research Team Meeting #10

November 14 (Fri) 16:00 - 17:00, 2025

Yoshiko Ogata (Professor, Research Institute for Mathematical Sciences (RIMS), Kyoto University)

Mathematical Application Research Team invites Prof. Yoshiko Ogata from RIMS for this meeting. Her talk title will be announced later. You are welcome to join the meeting. The title and the abstract of her talk are: Title: Mixed state topological order: operator algebraic approach Abstract: We consider anyons in mixed states of two-dimensional quantum spin systems within the operator-algebraic framework of quantum statistical mechanics. To each state satisfying a mixed-state version of approximate Haag duality, we associate a braided C*-tensor category, which we interpret as describing the anyonic excitations of the state. We then investigate how these anyonic structures behave under interactions with the environment.

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

Event Official Language: English

Contribution of star-forming galaxies to the cosmic gamma-ray background

November 14 (Fri) 14:00 - 15:15, 2025

Junling Chen (Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)

Fermi Gamma-Ray Space Telescope has measured the diffuse extragalactic gamma-ray background (EGB) radiation in the energy range of 100 MeV to 820 GeV. Several candidate γ -ray sources have been proposed as the candidate components of the unresolved EGB, including active galactic nuclei (AGNs), millisecond pulsars, dark matter annihilation, and star-forming galaxies (SFGs), but their quantitative contribution has not yet been precisely determined. In this talk, I will introduce our latest physical model describing the gamma-ray emission mechanism from SFGs, and our estimate of the contribution of SFGs based on careful calibration with gamma-ray luminosities of nearby galaxies and physical quantities (star formation rate, stellar mass, and size) of galaxies observed by high-redshift galaxy surveys.

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

Event Official Language: English

Mathematical Sciences Outreach Workshop 2025

November 14 (Fri) - 16 (Sun) 2025

This year's meeting on "Outreach of Mathematical Sciences" will be held from FRI NOV 14 12:30 to SUN NOV 16 15:00 as a face-to-face meeting at Institute of Mathematics for Industry of Kyushu University as "Outreach of Data Descriptive Science and Mathematical Sciences" supported by Grant-in-Aid for Transformative Research Areas (A), 2022-2026 "Establishing data descriptive science and its cross-disciplinary applications" in cooperation with RIKEN iTHEMS SUURI-COOL (Kyushu) using ZOOM for the necessary part as well.

Venue: W1-D-413, IMI Auditorium, Ito Campus, Kyushu University (Main Venue) / via Zoom

Event Official Language: Japanese

The Uchuu simulations data set: large-scale structures and galaxies - Tomoaki Ishiyama

November 13 (Thu) 14:00 - 15:30, 2025

Tomoaki Ishiyama (Associate Professor, Digital Transformation Enhancement Council, Chiba University)

I will introduce the Uchuu suite of large high-resolution cosmological N-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion dark matter particles in a box of side-length 2.0 Gpc/h, with particle mass of 3.27e8 Msun/h. The highest resolution simulation, Shin-Uchuu, consists of 262 billion particles in a box of side-length 140 Mpc/h, with particle mass of 8.97e5 Msun/h. Combining these simulations, we can follow the evolution of dark matter haloes and subhaloes spanning those hosting dwarf galaxies to massive galaxy clusters across an unprecedented volume from very high-z. We release N-body data (halo/subhalo catalogs and merger trees) and mock galaxy/AGN catalogs constructed using various models, which cover objects from z=0 to very high-z. These catalogs open a new window on understanding the large-scale structures and galaxy formation. In this presentation, I will also introduce results of cosmological simulations adopting a time-varying dark energy, conducted on the supercomputer Fugaku.

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

Event Official Language: English

DA Seminar: Machine learning for precipitation estimation and forecasting / Analysis of a Long-Lived Supercell: Life Cycle and Severe Weather Patterns in Northern Buenos Aires Province

November 13 (Thu) 10:30 - 12:00, 2025

Juan Ruiz (Visiting Scientist, Prediction Science Research Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
Luciano Vidal (Visiting Scientist, Prediction Science Research Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Title: Machine learning for precipitation estimation and forecasting Speaker: Dr. Juan Ruiz (University of Buenos Aires – CONICET) Abstract: Estimating and forecasting precipitation is essential for a wide range of human activities as well as for disaster prevention. In this talk we will discuss the application of deep neural networks to the estimation of precipitation with high time and spatial resolution, combining remote sensors and numerical weather predictions. The proposed models show that these information sources can be effectively combined to improve the accuracy of real-time precipitation estimates. Additionally, we will present the application of deep neural networks as a postprocessing tool for short-range deterministic and ensemble-based numerical weather predictions and for the quantification of their uncertainty. The performance of the machine-learning models in the quantification of the uncertainty is close to that achieved by the dynamical ensembles and can be even better in the presence of a model. Title: Analysis of a Long-Lived Supercell: Life Cycle and Severe Weather Patterns in Northern Buenos Aires Province Speaker: Dr. Luciano Vidal (National Meteorological Service, Argentina) Abstract: This work presents a detailed analysis of a long-lived convective supercell that affected the northern Buenos Aires province, Argentina, on March 19, 2024. The primary objective is to characterize its life cycle and associated severe weather patterns using an integrated multi-sensor approach. This methodology combines data from satellite imagery with documentation of surface damage caused by large hail and intense winds. The storm exhibited a remarkable longevity, traveling approximately 400 km over 5.5 hours and impacting a total of 11 municipalities before its dissipation. Throughout its trajectory, the supercell generated significant damage due to large hail and severe wind gusts that, in some areas, exceeded 150 km/h. Furthermore, the storm ultimately affected the Sarandí-Santo Domingo basin (the pilot basin of the Argentine-Japanese SATREPS/PREVENIR project) by generating flash floods. The results of this analysis provide crucial information for the improvement of forecasting and early warning systems for severe weather events in the region.

Venue: Hybrid Format (RIKEN R-CCS room 107 and Zoom)

Event Official Language: English

Topological physics and its interdisciplinary influence

November 12 (Wed) 13:00 - 14:00, 2025

Tomoki Ozawa (Professor, Advanced Institute for Materials Research (AIMR), Tohoku University)

Topological insulators are materials which do not conduct current inside but do conduct at the surface or the edge. The name "topological" comes from the fact that the "shape" of the wavefunction of electrons in topological insulators show non-trivial twist, which can be mathematically characterized by the language of topology. Alongside the development of the study of topological insulators in solids, analogous phenomena were found to exist also in other systems such as photonics, mechanics, geophysics, and active matter. In this seminar, I discuss how the underlying concept of "topology of states" can have a broad impact applicable to various areas in physics, with some emphasis on my own contribution to the field. I aim to structure the first half of my seminar to be accessible to those outside physics, and latter half to be more specialized, covering cutting-edge results.

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

Event Official Language: English