Mathematical Application Research Team Meeting #10

2025年11月14日(金) 16:00 - 17:00

緒方 芳子 (京都大学 数理解析研究所 (RIMS) 教授)

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.

会場: セミナー室 (359号室) 3階 359号室 (メイン会場) / via Zoom

イベント公式言語: 英語

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

2025年11月14日(金) 14:00 - 15:15

Junling Chen (東京大学 大学院数理科学研究科 博士課程)

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.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

数理科学のアウトリーチについての研究会 2025

2025年11月14日(金) - 16日(日)

今年の「数理科学のアウトリーチについての研究会」を、令和４年度ー８年度　文部科学省・科研費・学術変革領域 (A)「データ記述科学の創出と諸分野への横断的展開」のご援助のもとで、11月14日（金）12:30 ～16日（日）15:00 に「データ記述科学と数理科学のアウトリーチについての研究会」として、九州大学マス・フォア・インダストリ研究所で、対面とズームを併用して開催いたします。RIKEN iTHEMS（SUURI-COOL Kyushu）はこれを共催しています。

会場: 九州大学 伊都キャンパス IMI オーディトリアム W1-D-413 (メイン会場) / via Zoom

イベント公式言語: 日本語

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

2025年11月13日(木) 14:00 - 15:30

石山 智明 (千葉大学 情報戦略機構 准教授)

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.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

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

2025年11月13日(木) 10:30 - 12:00

フアン・ルイス (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 予測科学研究チーム 客員研究員)
ルチアーノ・ヴィダル (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 予測科学研究チーム 客員研究員)

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.

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

イベント公式言語: 英語

Topological physics and its interdisciplinary influence

2025年11月12日(水) 13:00 - 14:00

小澤 知己 (東北大学 材料科学高等研究所 (AIMR) 教授)

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.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

A genealogy-based framework to infer the demographic history, genetic structure, and phenotype association

2025年11月11日(火) 14:00 - 15:00

Charleston Chiang (Associate Professor, University of Southern California, USA)

We propose a conceptual analogy in population genetics to the central dogma of molecular biology. While the central dogma describes the flow of information from DNA to RNA to protein, we posit that under neutrality, a population's demography shapes its underlying genealogy, which in turn determines patterns of genetic variation that give rise to phenotypic variation. At the center of this analogous dogma is the genetic genealogies. Recent advances in inferring the Ancestral Recombination Graph (ARG), a complete record of a population's genealogies, have enabled us to develop a suite of methods that interrogates each stage these fundamental and connected components:

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

On the Role of Hidden States of Modern Hopfield Network in Transformer

2025年11月10日(月) 14:00 - 15:00

瀧 雅人 (立教大学 大学院人工知能科学研究科 准教授)

Large language models such as ChatGPT are based on deep learning architectures known as Transformers. Owing to their remarkable performance and broad applicability, Transformers have become indispensable in modern AI development. However, it still remains an open question why Transformers perform so well and what the essential meaning of their unique structure is. One possible clue lies in the mathematical correspondence between Hopfield Networks and Transformers. In this talk, I will first introduce the major developments over the past decade that have significantly increased the storage capacity of Hopfield Networks. I will then review the theoretical correspondence between Hopfield Networks and Transformers. Building on this background, I will present our recent findings: by extending this correspondence to include the hidden-state dynamics of Hopfield Networks, we discovered a new class of Transformers that can recursively propagate attention-score information across layers. Furthermore, we found, both theoretically and experimentally, that this new Transformer architecture resolves the “rank collapse” problem often observed in conventional multi-layer attention. As a result, when applied to language generation and image recognition tasks, it achieves performance surpassing that of existing Transformer-based models.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Towards the prediction of clusters of primordial black holes

2025年11月7日(金) 16:00 - 17:30

Danilo Artigas (京都大学 大学院理学研究科 物理学・宇宙物理学専攻 物理学第二教室 学振特別研究員PD)

Primordial black holes (PBHs) are a major candidate for dark matter, expected to form from the collapse of large density fluctuations generated during inflation. Their abundance is highly sensitive to non-linear effects, some of which can be described through the δN formalism. This approach models the universe as a set of locally homogeneous patches evolving independently throughout inflation. However, accounting for the spatial correlations between these patches is crucial to predicting the spatial distribution of PBHs and the formation of clusters. In this talk, after reviewing the δN formalism, I will show how to include spatial correlations within this framework. As an illustration, I will discuss the ultra-slow-roll model and compute the curvature perturbation ζ — necessary to determine PBH formation — and its spatial correlations at the end of inflation. In the future, this could enable the prediction of PBH binaries and clusters, which may leave observable imprints such as gravitational waves.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Rational function semifields of dimension one

2025年11月7日(金) 13:30 - 15:30

宋 珠愛 (九州大学 大学院数理学研究院 助教)

Recently some researchers gave many studies toward algebro-geometric foundation for tropical geometry. I focused on rational function semifields of tropical curves and characterized them. With this characterization, in this talk, I suggest a definition of ``rational function semifield of dimension one". This definition can write out weight in the term of $\boldsymbol{T}$-algebra homomorphism, and can write balancing condition together with harmonic functions, where both weight and balancing condition are fundamental concepts for tropical varieties and $\boldsymbol{T}$ is the tropical semifield $(\boldsymbol{R} \cup \{-\infty\}, \operatorname{max}, +)$.

会場: セミナー室 (359号室) / via Zoom

イベント公式言語: 日本語

Pairing in Bose-Fermi and Fermi-Fermi systems

2025年11月6日(木) 15:00 - 16:30

Pierbiagio Pieri (Associate Professor, Dipartimento di Fisica e Astronomia “Augusto Righi”, Università di Bologna, Italy)

This seminar is co-hosted by GWX-EOS Working Group and iTHEMS-ABBL Joint Astro Study Group. Abstract: In the first part of my talk, I will review recent work on Bose-Fermi mixtures with an attractive interaction inducing pairing between bosons and fermions. After discussing a recent experiment on this system [1], which has confirmed predictions obtained by us some time ago within a many-body diagrammatic approach [2], I will present novel results for the compressibility [3] that suggest a metastable nature for the many-body phase observed in [1]. Then, I will discuss the extension of our calculations to two-dimensional Bose-Fermi mixtures [4,5]. The results obtained in 2D challenge previous beliefs formulated for 3D systems. In the second part, I will discuss attractive polarized Fermi systems, for which the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase was proposed many years ago as a possible superfluid phase. I will discuss how significant precursor FFLO fluctuation effects appear already in the normal phase of polarized Fermi gases at finite temperature [6], and how they could be experimentally detected with ultracold gases. At zero temperature [7], I will discuss how the quasi-particle parameters of the normal Fermi gas change when approaching an FFLO quantum critical point, with a complete breakdown of the quasi-particle picture analogous to what found in heavy-fermion materials at an antiferromagnetic quantum critical point. Finally, I will discuss a recent joint experimental-theoretical work on the motion of a vortex orbiting a pinned anti-vortex in a strongly interacting Fermi gas [8], highlighting the interplay between Andreev bound states in the vortex core and delocalized thermal excitations in shaping the vortex dynamics.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Semiotic Rupture and the Emergence of Writing: Toward a Multimodal Model of Representational Innovation

2025年11月6日(木) 13:00 - 14:00

Joshua Englehardt (Professor, Center of Archeologist Studies, El Colegio de Michoacán, Mexico)
Michael D. Carrasco (Associate Dean for Research / Associate Professor, College of Fine Arts, Florida State University, USA)

Writing is a unique—and distinctively human—creation, one which arose independently in only six locations worldwide. From these primary sites of innovation, this relatively recent technology spread across the world. Its development is routinely lauded as one of humanity’s most important inventions, among its “greatest intellectual and cultural achievements,” and a key to human evolution. The scholar Florian Coulmas labels it “the single most important sign system ever invented on our planet. This presentation presents a theoretical framework for modeling the emergence, development, and structure of writing and other visual representational systems through a formal, processual lens. Building on Noam Chomsky’s distinction between internal language (I-language) and its externalization as E-language, we model writing as the mediated product of E-language and propose a set of visual analogues: I-image and E-image, understood as structurally similar generative systems. We offer a formal, cross- and multimodal model of writing and its development that treats it not as a codified extension of speech, but as a recursive reorganization of visual and linguistic generative systems. Rather than asking what writing is, we ask how it and other semiotic systems emerge. What tensions, pressures, and interactions catalyze their formation, transformation, and typological diversity? We contend that the semiotic dynamics that give rise to writing are not isolated or unique events, but are grounded in deeper processes, such as those underlying the emergence of image-making, that are already established in the cognitive evolution of Homo sapiens and plausibly present in ancestral hominins. That is, we see writing not as a spontaneous invention but as an emergent semiotic modality grounded in cognitive evolution and cultural externalization.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Introduction to Game Theory #2

2025年11月6日(木) 11:00 - 12:00

村瀬 洋介 (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 数理社会科学チーム チームディレクター)

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 lecture, we will discuss mixed-strategy Nash equilibria and their computational complexity.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Quantum multi-body problems using unsupervised machine learning

2025年11月5日(水) 15:00 - 16:00

内藤 智也 (東京大学 大学院工学系研究科 原子核国際専攻 特任助教)

I will introduce the recent development of a method to calculate the (anti)symmetrized wave functions and energies of the ground and low-lying excited states using the unsupervised machine learning technique. I will also introduce the recent attempts to consider the spin-isospin degrees of freedom and extend them to the Dirac equation.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Introduction to Lean theorem prover

2025年10月31日(金) 14:00 - 17:00

水野 勇磨 (Postdoctoral Researcher, University College Cork, Ireland)

A theorem prover is a tool for the formalization of mathematics, that is, for rigorously expressing and verifying theorems and proofs on a computer. In recent years, the Lean theorem prover has seen progress in the formalization of a wide range of areas of mathematics. In this talk, I will explain formalization of mathematics in Lean from the basics and survey the formalized results achieved to date.

会場: via Zoom / セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

5th ComSHeL Seminar

2025年10月31日(金) 11:00 - 12:00

小谷 元子 (理化学研究所 領域総括)

Title: Discrete Geometric Analysis and its application to materials science Abstract: Discrete Geometric Analysis is a discrete version of Geometric Analysis. It is however not just its discretization but a development of methods to bridge discrete and continuum. I will explain those and share some applications to materials science with you.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催 (メイン会場) / via Zoom

イベント公式言語: 英語

Operational Quantum Frames: from quantum mechanics to quantum field theory and beyond

2025年10月30日(木) 16:00 - 17:00

Jan Głowacki (Postdoc, Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Austria)

In this talk I will begin with a concise overview of the development of the operational approach to quantum reference frames (QRFs), tracing the line from its foundational contributions to its most recent applications. I will then introduce the central ideas of the research direction that I am pursuing which aims at developing relational foundations for relativistic quantum physics. The starting point is the application of the operational QRF formalism to the context of the Poincaré group, and establishing connections between this emerging framework and existing formalisms in quantum field theory. This part of the talk will summarize results from a recent preprint written with Samuel Fedida [1]. I will conclude by outlining a number of open research directions, highlighting selected topics in more detail depending on the available time and the interests of the audience

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語

Primordial black holes formation and its origin in inflation - Jianing Wang

2025年10月30日(木) 14:15 - 16:00

Jianing Wang (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 特任研究員)

Primordial black holes (PBHs) are thought to form through gravitational collapse of regions with excessively large density in the early universe, and they could serve as seeds for the formation of galaxies. They are also considered one of the important candidates for cold dark matter (DM). Detecting and constraining the abundance of PBHs can provide an effective constraint on realistic inflationary models. In this talk, I will combine inflation models with gravitational waves (GWs) to discuss cosmological phenomena related to primordial black holes. In particular, I will emphasize a simplified toy model of inflation, which naturally enhances the small-scale scalar perturbations by gluing together two linear potentials with different slopes. The enhanced perturbations can not only generate primordial black holes but also emit gravitational waves through higher-order perturbations. This research demonstrates the significant potential of primordial black hole studies, and it naturally leads to a crucial question of how to accurately estimate the PBH abundance. In the latter part of the talk, I will introduce how to use peaks theory to estimate the abundance of primordial black holes. Our new method works well for any form of the power spectrum, and considering the use of more systematic statistical methods, we believe it is currently the most precise approach in the academic community.

会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催

イベント公式言語: 英語

Inferring Phylogenetic Networks in the Genomic Era

2025年10月30日(木) 13:00 - 14:00

孔 星植 (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 研究員)

While phylogenetic trees (i.e., branching diagrams that depict the evolutionary history of different organisms) have been essential for understanding species evolution, they do not fully capture certain evolutionary processes, such as hybridization. In these cases, a phylogenetic network, which extends a phylogenetic tree by allowing two branches to merge into one and create reticulations, is needed. However, existing methods for estimating networks from genomic data become computationally prohibitive as dataset size and topological complexity increase. In this talk, I present the performance of popular computational methods that detect hybridization from genomic data as an alternative to the network inference, discussing their significance and limitations. I then explain how phylogenetic networks generalize trees to represent complex evolutionary histories and explore the biological interpretations that can be drawn from various branching patterns. Finally, I introduce PhyNEST (Phylogenetic Network Estimation using SiTe patterns), a novel method that efficiently and accurately infers phylogenetic networks directly from sequence data using composite likelihood. PhyNEST is implemented as an open-source Julia package and is available at https://github.com/sungsik-kong/PhyNEST.jl.

会場: 研究本館 3階 359号室 (メイン会場) / via Zoom

イベント公式言語: 英語

Lectures on Neutron Star Structure IV

2025年10月28日(火) 15:30 - 17:00

Mark Alford (Professor, Washington University in St. Louis, USA)

This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I : Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.

会場: セミナー室 (359号室) (メイン会場) / via Zoom

イベント公式言語: 英語