セミナー

Separability criteria for loops via the Goldman bracket

2025年9月12日(金) 15:00 - 17:00

和久田 葵 (東京大学 大学院数理科学研究科 博士課程)

In this talk, we give algebraic criteria using the Goldman bracket to determine whether two free homotopy classes of loops on an oriented surface have disjoint representatives. As an application, we determine the center of the Goldman Lie algebra of a pair of pants. We extend Kabiraj's method, which was originally limited to oriented surfaces filled by simple closed geodesics, and show that in this case, the center is generated by the class of loops homotopic to a point, and the classes of loops winding multiple times around a single puncture or boundary component.

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

Neural Network for Holographic QCD

2025年9月12日(金) 10:30 - 11:30

ホーンアン・ツオン (Ph.D. Candidate, College of Physics, Jilin University, China)

Holographic QCD provides a powerful theoretical framework for investigating the equation of state of boundary field theories, where the idea is that the boundary dynamics can be fully determined by solving the bulk equations of motion. However, the coupling functions in the action typically rely on external inputs (such as lattice QCD data), and their explicit forms are often based on artificial assumptions. To eliminate such arbitrariness, we introduce neural networks into the potential reconstruction framework to represent the coupling functions, thereby constructing a fully data-driven machine learning model governed solely by boundary field theory inputs. The results obtained after training show remarkable consistency with the coupling functions derived from holographic renormalization based on prior assumptions, highlighting the strong function-approximation capability of neural networks and revealing the potential to unify the potential reconstruction and holographic renormalization approaches within a common framework.

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

Identifying signatures of natural selection through the genome using mixed models

2025年9月11日(木) 13:00 - 14:00

リュカ・ソール (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 数理遺伝学理研ECL研究ユニット 特別研究員)

Identifying signatures of selection has traditionally relied on detecting traces in modern day genomes. In particular, the length of linkage disequilibrium (LD) blocks in modern day genomes has often been used as an indicator of selection. However, in recent years, the emergence of ancient DNA has enabled new approaches to infer selection that directly use genetic data from the past and reconstruct the evolutionary history of genomes. In this presentation, I will introduce a methodological framework that was recently proposed to identify variants under selection across the genome: mixed models. Mixed models have long been applied in the Genome-Wide Association Study (GWAS) literature, as they effectively account for population structure and easily integrate confounders. In this context, I will present the framework and outline our plans to further improve current approaches.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Covariance Localization Local ensemble transform Kalman filter (LETKF)

2025年9月10日(水) 13:00 - 14:00

ウナシシュ・モンダル (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 特別研究員)

会場: 計算科学研究棟 R511 (メイン会場) / via Zoom

イベント公式言語: 英語

Foundations of Relational Quantum Field Theory — scalars

2025年9月9日(火) 16:30 - 17:30

Samuel Fedida (PhD, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK)

We develop foundations for a relational approach to quantum field theory (RQFT) based on the operational quantum reference frames (QRFs) framework considered in a relativistic setting. We focus on scalar fields in Minkowski spacetime and discuss the emergence of relational local observables and pointwise fields from the consideration of Poincaré-covariant frame observables defined over the space of inertial reference frames. We recover a relational notion of Poincaré covariance, with transformations on the system directly linked to the state preparations of the QRF. We introduce various causality conditions which mirror standard Einstein causality and microcausality, now seen in a relational context. The theory makes direct contact with established foundational approaches to QFT: the vacuum expectation values derived within our framework reproduce many of the essential properties of Wightman functions, and we compare the proposed formalism with Wightman QFT with the frame smearing functions describing the QRF's localisation uncertainty playing the role of the Wightmanian test functions. We show how the algebras generated by relational local observables satisfy all of the core axioms of Algebraic QFT. This work is an early step in revisiting the mathematical foundations of QFT from a relational and operational perspective.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Exciting Possibilities of Multi-Messenger Windows on Cosmic Accelerators

2025年9月9日(火) 13:30 - 15:00

安田 航一朗 (Ph.D. Student, Department of Physics and Astronomy, University of California, Los Angeles, USA)

Active Galactic Nuclei (AGN) jets are among the most extreme particle accelerators in the universe and are thought to play a key role in the origin of ultra-high-energy cosmic rays. Yet, the physical processes inside these jets, particularly those involving heavy nuclei, remain poorly understood. In this talk, I will explore how nuclear and atomic processes in AGN jets can leave distinctive multi-messenger signatures, from neutrino production via nuclear decays to characteristic gamma-ray features from nuclear excitations. These phenomena offer a new window into the microscopic physics of nuclei under astrophysical extreme conditions, while also serving as macroscopic probes of jet composition and acceleration mechanisms. I will also discuss how upcoming observations, including neutrino flavor studies and MeV gamma-ray missions, could provide critical tests of these ideas and shed light on the role of nuclear physics in shaping cosmic accelerators.

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

Computer Algebra with Deep Learning

2025年9月5日(金) 15:00 - 17:00

石原 侑樹 (日本大学 理工学部 数学科 助教)

Computer algebra is a field that aims to perform various mathematical calculations on computers. In recent years, there has been a surge in efforts to accelerate computer algebra algorithms using deep learning models such as “Transformer,” which is used in ChatGPT. In this lecture, I will introduce the results of joint research with Professor Kera et al. on learning Gröbner bases with Transformer.

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

8th Mathematical Application Research Team meeting

2025年9月5日(金) 10:30 - 11:50

ソニア・マムーディ (東北大学 材料科学高等研究所 (AIMR) 数学連携グループ 助教)

The 8th meeting of the Mathematical Application Research Team invites Sonia Mahmoudi for a talk.

会場: via Zoom / 理化学研究所 和光キャンパス 3階 359号室

イベント公式言語: 英語

Geometry of 2d topological field theories and integrable hierarchies

2025年9月4日(木) 15:00 - 17:00

テツ・オウ (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)

In this talk, I will explain a mathematical formulation of 2d topological field theories making use of integrable hierarchies, which is a framework initiated by B. Dubrovin and developed by many other mathematicians. The talk is divided into two parts. The first 45 minutes is a gentle introduction on how the mathematical structure called Frobenius manifolds naturally appears from topological field theories. The remaining part of the talk is devoted to explaining relationships between Frobenius manifolds and integrable hierarchies via the example of the KdV hierarchy.

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

Synthesizing the evolutionary invasion analysis for high-dimensional population dynamics

2025年9月4日(木) 13:00 - 14:00

入谷 亮介 (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 上級研究員)

I will present a linear-algebraic (spectral) method for analyzing nonnegative matrices to study the dynamics of natural selection. This is a joint project with Troy Day (Queen's University, Canada). Within adaptive dynamics theory, evolutionary invasion analysis provides a powerful framework for studying adaptive evolution. It allows us to evaluate (i) whether a new type of individuals (mutants) can successfully invade and replace the resident type, and (ii) whether recurrent substitutions converge to an equilibrium that resists further invasion (an evolutionary Nash equilibrium). A central task is to quantify the reproductive success of mutants, which corresponds to computing the spectral radius (largest eigenvalue) of a nonnegative matrix. However, the high dimensionality of population dynamics often makes the analytical treatment of eigenvalues intractable. To address this problem, we have developed a methodology that applies to any high-dimensional adaptive dynamics system. I will first introduce the principles of adaptive dynamics and the associated eigenvalue problem. I will then present our new method, which translates the high-dimensional eigenvalue problem into another, lower-dimensional eigenvalue problem of arbitrary size, using (i) Perron–Frobenius theory and (ii) graph-theoretic arguments.

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

Ensemble transform Kalman filter (ETKF)

2025年9月3日(水) 13:00 - 14:00

岩中 達郎 (理化学研究所 計算科学研究センター (R-CCS) データ同化研究チーム リサーチアソシエイト)

会場: 計算科学研究棟 R511 (メイン会場) / via Zoom

イベント公式言語: 英語

A Fresh Look at Late-Time Hawking Radiation

2025年9月2日(火) 14:00 - 15:30

ウェイシャン・シャオ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 基礎科学特別研究員)

There is now a common belief that non-perturbative quantum gravity effects are relevant for resolving the black hole information puzzle. But could such effects also largely alter Hawking radiation itself, the main culprit that led to the puzzle in the first place? There are two main lessons that I would like to convey from this presentation: 1. For large black holes formed by dynamical collapse, the usual description of Hawking radiation in the low-energy effective theory breaks down at an early stage, signaling the need for a UV theory to describe the origin of late-time radiation. 2. In UV models of the radiation field that incorporate a form of nonlocality motivated by string theory, Hawking radiation becomes a transient phenomenon that occurs only for a brief period of time. This behavior suggests a major deviation from the conventional picture of black hole evaporation based on local quantum field theory.

会場: via Zoom / 理化学研究所 和光キャンパス 3階 359号室

イベント公式言語: 英語

Dust formation in the universe: reconstructing of theoretical models

2025年8月29日(金) 14:00 - 15:15

田中 今日子 (東京女子大学 現代教養学部 情報数理科学科 特任准教授)

The formation process of cosmic dust is the starting point of solid matter and is important for understanding the evolution of cosmic material and planet formation processes. The nucleation process at the initial stage of the phase transition is a key to how cosmic dust is formed and evolves. Recent studies of the nucleation have shown possibilities that are very different from the theoretical models that have been considered so far. We have investigated the nucleation process using molecular dynamics simulations, which allow us to observe the nucleation process at the molecular level and obtain new information. We also present our attempt to develop and reconstruct a new theoretical model to elucidate a comprehensive picture of cosmic dust formation in collaboration with experiments.

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

Shadow formation in gravitational collapse: redshift and blueshift by spacetime dynamics

2025年8月28日(木) 16:00 - 17:30

古賀 泰敬 (大阪工業大学 情報科学部 情報知能学科 助教)

A black hole illuminated by a background light source is observed as a black hole shadow. For a black hole formed by the gravitational collapse of a transmissive object, redshift of light due to the spacetime dynamics is expected to play a crucial role in the shadow formation. In this talk, we investigate the redshift of light caused by the spacetime dynamics. First, we consider a spherical shell model. We see that the collapse of a shell typically leads to the redshift of light, while blueshift can be also observed in some cases. This result suggests that a shadow image is generally formed in the late stage of the gravitational collapse of a transmissive object. Second, we consider a general, dynamical, spherically symmetric spacetime and propose a new covariant formula for the redshift of light. This formula relates the dynamical redshift to the energy-momentum tensor of the background spacetime and provides its intuitive interpretation with Newtonian analogy.

会場: via Zoom / 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

The link between ecology and evolution in the speciation process

2025年8月28日(木) 13:00 - 14:00

ホセ サイード・グティエレス オルテガ (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)

Both ecological and evolutionary processes shape biodiversity, but these are usually studied separately. Ecologists focus on current dynamics, while evolutionary biologists examine long-term changes. The intersection between the two perspectives lies in understanding speciation: the process of how new species arise. Understanding speciation can clarify how ecological processes build up into the global patterns we see in evolution, and in turn, how evolutionary trends promote ecological processes. Using observational data compiled from macroecological and phylogenetic methods on multiple plant and animal groups, I suggest that the ecological patterns left by the factors promoting speciation in a community correspond to the speciation/extinction dynamics within that community. This ecological-phylogenetic correspondence represents a connection between the ongoing and the long-term dynamics, an idea that may unify the disciplines of ecology and evolution. I expect this talk can promote discussion on the topics of eco-evolutionary dynamics, so that I can get some feedback from you, and that we can create chances for collaboration.

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

磁気回転効果による中性子星の自転と中性子スピンの間の角運動量変換

2025年8月28日(木) 10:00 - 12:00

舟木 博志 (慶応義塾大学 理工学部 特任助教)

[NOTE] 本インフォーマルセミナーは長瀧天体ビッグバン研究室により主に企画されており、日本語で行われます。また、GWX-EOS Working Group および iTHEMS-ABBL Joint Astro Study Groupとのジョイントイベントです。 概要: 本講演では、中性子星のクラストとコアの間で角運動量が交換される新たなメカニズムを、磁気回転効果を介して提案する。拡張された流体力学を用いることで、中性子星の自転に相当するマクロな角運動量と、中性子の軌道およびスピンから生じるミクロな角運動量の相互作用を取り込む。クラストにおけるマクロスケールな回転がコア内のミクロスケール角運動量に影響を与え、中性子スピン偏極を引き起こすことを明らかにし、(反)グリッチの代替シナリオを提案する。本研究は、中性子星物理学でこれまで見逃されていたマルチスケール角運動量相互変換を浮き彫りにし、磁気回転天文学の新たな道が拓かれると期待される。

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: 日本語

Analysis of inflationary models in higher-dimensional uniform inflation

2025年8月27日(水) 16:00 - 18:00

廣瀬 拓哉 (九州産業大学 教育研究施設 基礎教育サポートセンター 特任助教)

In this talk, we consider higher-dimensional uniform inflation, in which the extra dimensions expand at the same rate as three-dimensional non- compact space during inflation. We compute the cosmological perturbation in $D+4$ dimensions and derive the spectral index $n_s$ and the tensor- scalar ratio $r$. We analyze five inflationary models: chaotic inflation, natural inflation, quartic hilltop inflation, inflation with spontaneously broken SUSY, and $R^2$ inflation. By combining the results from these models with the Planck 2018 constraints, we discuss that it is not desirable for the extra-dimensional space to expand at the same rate as the three-dimensional non-compact space, except for the case of one extra dimension. This talk is based on arXiv:2501.13581[hep-ph].

会場: セミナー室 (359号室)

イベント公式言語: 英語

Observational constraint of non-scalar phantom dark energies

2025年8月26日(火) 16:00 - 17:30

Hsu-Wen Chiang (Postdoc, Department of Physics, Southern University of Science and Technology, China)

Recent observation of DESI strongly disfavors cosmological constant. Given the lack of constraint regarding the fundamental field that constitutes a dynamical dark energy, people traditionally resort on a hypothetical scalar field. We instead consider minimally coupled non-spinless field as alternative, specifically the extended Proca-Nuevo theory (spin-1) and 3-form field (spin-3). Both theories at the background level permit pure phantom (w < -1) and phantom crossing (w < -1 to w > -1) scenarios. Furthermore, with reasonable choice of EFT parameters we can decouple the scalar perturbation of the dark energy from the matter sector. However, the Lorentz constraint within the higher-spin field inevitably modifies the response of the scalar potential to the matter perturbation. This leads to an enhancement of the matter power spectrum most obvious in BAO fullshape analysis. We then perform MCMC analysis and show that the Hubble tension is alleviated, and the non-spin-0 models are preferred marginally over a cosmological constant.

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 Discussion on Quantum Machine Learning for Medical Data

2025年8月26日(火) 14:00 - 15:00

杉本 聡 (理化学研究所 数理創造研究センター (iTHEMS) 数理展開部門 医科学データ駆動数理チーム 上級研究員)

Our team is investigating the applicability of machine learning using quantum computers to medical data. In this talk, we will provide a brief overview of supervised machine learning for medical data as a topic for discussion.

会場: via Zoom

イベント公式言語: 英語

Tamely Ramified Geometric Langlands Correspondence

2025年8月22日(金) 15:00 - 19:00

Yuki Matsubara (Ph.D. Student, Centre for Quantum Mathematics, University of Southern Denmark, Denmark)

The geometric Langlands correspondence (GLC) is a geometric analogue of the Langlands conjecture in number theory, relating algebraic geometry, representation theory, and many other areas. Since A. Kapustin and E. Witten pointed out the relation between GLC and mirror symmetry, there have been various studies on GLC from a physics perspective as well as a mathematical perspective. First talk: An introduction to Langlands conjecture for everyone This is an entirely accessible overview of the Langlands conjecture. Starting from famous topics, such as the Pythagorean theorem and Fermat’s Last Theorem, I will introduce the statement and motivations behind the Langlands conjecture. No prior background will be assumed, and technical details will often be sketched rather than fully developed, so that anyone with a general mathematical curiosity can follow along. Second talk: On a certain tamely ramified geometric Langlands correspondence In this talk, I will present my research. Arinkin’s 2001 result established the geometric Langlands correspondence for the case G = SL2 on the complex projective line P1 with four fixed regular singularities. When one attempts to extend this to five or more singularities, it turns out to be more natural to decompose the correspondence into a Radon transform-type correspondence and a “GLC‑like” correspondence. I will report on the calculations of cohomology that support the proof of this GLC‑like correspondence in the P1 with five fixed regular singularities case.

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