Basic Conceptual and Mathematical Problems of QFT

2026年2月20日(金) 14:00 - 15:30

クリスティ・コウジ・ケリー

In this talk we discuss some of the most basic conceptual and mathematical difficulties that arise in the standard physics analysis of QFT. In particular we shall discuss the origin of UV divergences in QFT—pointing out that there is both a kinematic and a dynamic aspect to this problem, and that the standard physics explanation (’new physics’) only considers the latter—and suggest that despite the notoriety of the problem, UV divergences are essentially under control. Secondly we discuss Haag’s theorem—which ensures the nonexistence of the interaction picture and the triviality of the perturbative S-Matrix—and indicate how this is the most elementary manifestation of a series of infrared problems in QFT. Finally we will outline why the rigorous construction of path-integral measures is difficult. If we have time, we may discuss some difficulties associated with gauge theories such as the infraparticle problem of QED and the mass-gap problem of Yang-Mills theory.

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

Tunneling with physics-informed renormalisation group flows in the anharmonic oscillator

2026年2月20日(金) 10:00 - 11:00

Friederike Ihssen (Postdoctoral Fellow, Physics, Ruhr University Bochum, Germany)

The resolution of strongly correlated physical systems is computationally hard, but can be simplified enormously by a formulation in terms of suitable dynamical degrees of freedom. Within the functional renormalisation group framework, physics-informed renormalisation group flows (PIRG flows) [1] implement scale-dependent coordinate transformations that can be used to devise optimal expansion schemes around such degrees of freedom. Recently, we have applied PIRG flows to the anharmonic oscillator, with an emphasis on the weak coupling regime with its instanton-dominated tunnelling processes [2]. We show that the instanton physics behind the exponential decay of the energy gap is already covered in the first order of the derivative expansion of the PIRG. The crucial new ingredients in the present analysis are the use of the ground state expansion within PIRG flows, as well as precision numerics based on Galerkin methods. Our result a_inst = 1.910(2) for the decay constant is in quantitative agreement with the analytic one, a_inst = 1.886 with a deviation of 1%. This illustrates very impressively the capacity of the PIRG for fully capturing non-perturbative physics already in relatively simple approximations.

会場: via Zoom / 研究本館

イベント公式言語: 英語

Spectral Codes : A Geometric Formalism for QEC

2026年2月19日(木) 15:00 - 16:30

菅野 聡 (ソフトバンク株式会社 先端技術研究所 研究員)

In this talk, I will introduce a novel geometric framework for quantum error correction based on spectral triples in noncommutative geometry. In this formulation, quantum error-correcting codes are described as spectral projections onto the low-energy eigenspaces of Dirac-type operators, where the separation between logical information and local errors is captured geometrically. This approach provides a unified spectral and geometric understanding of key properties such as code distance and error thresholds. Moreover, it accommodates various existing codes, including classical linear codes, stabilizer codes, GKP codes, and topological codes. This geometric perspective also suggests intriguing connections to deformation quantization and holographic quantum error correction, offering promising directions for future research.

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

Binary neutron Star Merger as a Probe of Hadron-Quark Transition

2026年2月19日(木) 14:00 - 15:00

黄 永嘉 (Research Associate, Purple Mountain Observatory, Chinese Academy of Sciences, China)

This seminar is a joint seminar between GWX-EOS and the iTHEMS-ABBL Joint Astro SG. The recent rise of multi-messenger astronomy—including radius measurements from NICER, tidal deformability constraints from gravitational-wave events GW170817, and first-principles calculations from chiral effective field theory (χEFT) and perturbative QCD—has significantly tightened constraints on the neutron star equation of state. These advances consistently point to a non-monotonic sound speed in dense matter, suggesting that the cores of massive neutron stars may host exotic phases such as quark matter. However, the masquerade effect in static neutron stars makes it difficult to directly probe the nature of the transition (e.g., a smooth crossover or a sharp phase transition) near the core through observation alone.

会場: 理化学研究所 和光キャンパス (メイン会場) / via Zoom

イベント公式言語: 英語

The sample complexity of species tree estimation: How many genes does it take to infer a species tree?

2026年2月19日(木) 13:00 - 14:00

Max Hill (Assistant Professor, University of Hawaiʻi, USA)

In this talk, I will discuss the problem of inferring an evolutionary tree from DNA sequence data. The main focus will be on the sample complexity of this problem---i.e., the question of how much data is required to achieve high probability of correct inference. After introducing a standard stochastic model of gene and DNA evolution, I will highlight some surprising features of DNA sequence data that complicate inference. Finally, I will present an impossibility result which takes the form of an information-theoretic lower bound on the minimum amount of data needed for accurate inference when genes exhibit variation in mutation rates. No prior knowledge of phylogenetics or information theory is assumed. Based on joint work with Sebastien Roch.

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

第31回 MACSコロキウム・2025年度MACS成果報告会

2026年2月18日(水) 14:45 - 18:00

衞藤 雄二郎 (京都大学 大学院理学研究科 附属サイエンス連携探索センター (SACRA) 准教授)

14:45-15:00 ティータイムディスカッション [15:00-16:00 第31回MACSコロキウム 講演] 衞藤 雄二郎（京都大学大学院理学研究科 附属サイエンス連携探索センター 准教授）「明るい量子光源を使った量子計測」 [16:10-18:30 2025年度MACS成果報告会] 16:10-17:10 各スタディグルーブ フラッシュトーク 17:10-18:00 参加学生によるポスター発表

会場: 京都大学 理学研究科 6号館401号室（建物配置図（北部構内）【4】の建物）

イベント公式言語: 日本語

Brainstorming session on data assimilation with quantum computing

2026年2月18日(水) 14:00 - 16:00

三好 建正 (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 チームプリンシパル)

We will discuss the potential of quantum computing for applications in data assimilation.

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

Taming the Butterfly: A New "Duality Principle" Turns Chaos into Control

2026年2月18日(水) 13:00 - 14:00

三好 建正 (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 チームプリンシパル)

Data Assimilation (DA) is the backbone of modern weather forecasting. It integrates observational data into computer simulations to synchronize the model with nature. The Duality Principle posits that chaos control is mathematically the "twin" (dual) of DA. Data Assimilation: Uses observations to synchronize the Model to Nature. Chaos Control: Uses interventions to synchronize Nature to a desired Model ("target trajectory"). "The butterfly effect has long been a symbol of unpredictability," says Dr. Miyoshi. "But I asked a simple question: If a butterfly's wings can change the future, does that not imply that with the right, tiny push, we could choose a better future?" Instead of suppressing the chaotic system with massive force, this method acts like mathematical judo—leveraging the system's inherent instability. By applying minute, calculated "interventions" (analogous to the butterfly's flap), the system can be guided toward a "target trajectory"—for instance, shifting real-world conditions just enough to align with a model-simulated scenario where a typhoon causes no damage. Once synchronized, control becomes much easier to maintain. This study establishes the theoretical foundation for "Control Simulation Experiments" (CSE), a framework previously proposed by Miyoshi’s team. It provides a roadmap for future disaster prevention research, moving beyond passive prediction to active mitigation. Beyond meteorology, this general framework is expected to serve as a universal tool for studying interventions in various chaotic systems, from ecosystems to economics. Following the seminar, we will hold an informal discussion (brainstorming) on data assimilation with quantum computing in the same room from 2-4 pm.

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

The Rectangular Peg Problem and microlocal sheaf theory

2026年2月17日(火) 14:00 - 15:00

池 祐一 (東京大学 大学院数理科学研究科 准教授)

The Square Peg Problem asks whether every Jordan curve in the plane contains four distinct points that form the vertices of a square. This problem was proposed by Toeplitz in 1911 and remains unsolved in full generality. It can be generalized to the Rectangular Peg Problem, which concerns the existence of inscribed rectangles with a prescribed aspect ratio. Recently, Greene and Lobb successfully applied techniques in symplectic geometry to the problem and obtained new results. In this talk, I will explain how microlocal sheaf theory allows us to further extend their approach and affirmatively solve the Rectangular Peg Problem for a large class of Jordan curves, including all curves of finite length. This is joint work with Tomohiro Asano.

会場: セミナー室 (359号室)

イベント公式言語: 英語

Persistent homology and its applications

2026年2月17日(火) 11:00 - 12:00

池 祐一 (東京大学 大学院数理科学研究科 准教授)

Persistent homology is one of the main tools in topological data analysis (TDA), which encodes the topological features of given data into persistence diagrams. It has been successfully applied to various fields such as material science and computer graphics. In this talk, I will provide an overview of persistent homology and its applications. Furthermore, I will also discuss its integration with machine learning, specifically how persistent-homology-based loss functions can be used to regularize the topological structure of parameters.

会場: セミナー室 (359号室)

イベント公式言語: 英語

Monitoring the complexity and dynamics of mitochondrial translation

2026年2月12日(木) 16:00 - 17:00

脇川 大誠 (理化学研究所 開拓研究所 (PRI) 岩崎RNAシステム生化学研究室 リサーチアソシエイト)

Since mitochondrial translation leads to the synthesis of the essential oxidative phosphorylation (OXPHOS) subunits, exhaustive and quantitative delineation of mitoribosome traversal is needed. Here, we developed a variety of high-resolution mitochondrial ribosome profiling derivatives and revealed the intricate regulation of mammalian mitochondrial translation. Harnessing a translation inhibitor, retapamulin, our approach assessed the stoichiometry and kinetics of mitochondrial translation flux, such as the number of mitoribosomes on a transcript, the elongation rate, and the initiation rate. We also surveyed the impacts of modifications at the anticodon stem loop in mitochondrial tRNAs (mt-tRNAs), including all possible modifications at the 34th position, in cells deleting the corresponding enzymes and derived from patients, as well as in mouse tissues. Moreover, a retapamulin-assisted derivative and mito-disome profiling revealed mitochondrial translation initiation factor (mtIF) 3-mediated translation initiation from internal open reading frames (ORFs) and programmed mitoribosome collision sites across the mitochondrial transcriptome. Our work provides a useful platform for investigating protein synthesis within the energy powerhouse of the cell.

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

Recent progress in the resource theory of asymmetry and its applications

2026年2月12日(木) 13:30 - 15:00

田島 裕康 (九州大学 大学院システム情報科学研究院 情報学部門 准教授)

If you are not affiliated with RIKEN, please register using the registration form. Registration deadline: 12nd Feb. (Thu), 2026 Symmetry and symmetry breaking are among the central themes in physics and have attracted the interest of many physicists. Recently, the resource theory of asymmetry (RTA) [1-4], which approaches these issues from the perspective of resource theories, has been actively studied. In the past few years, several foundational advances have been made in this framework. In particular, the iid-complete monotone that plays a role analogous to entanglement entropy has been identified for arbitrary compact Lie groups [2] as well as for arbitrary finite groups [3]. The resolution for compact Lie groups includes, as a corollary, a solution to the Marvian–Spekkens conjecture [4]. Building on this theoretical foundation, several developments related to the Wigner–Araki–Yanase (WAY) theorem [5-7] have also been obtained. These include extensions of the WAY theorem to the implementation of arbitrary unitary gates [8], and a unification of the WAY-type theorems, i.e. the WAY theorem, the Eastin–Knill theorem (a fundamental limitation on error correction under symmetry) [9], and the above unitary-gate results. The unification is formulated a universal trade-off inequality relating symmetry, irreversibility, and quantumness for arbitrary quantum dynamics [10]. Using this tradeoff relation, the WAY-type limitations can now be applied, for example, to quantum thermodynamics[11] and black hole evaporation [10] etc. If time permits, I will also briefly touch upon some other recent developments, such as extensions of the above tradeoff and the WAY theorem to general resource theory beyond symmetry [12].

会場: セミナー室 (359号室) 3階 359号室

イベント公式言語: 英語

Quantum Electrodynamics of Strong Laser-Matter Interaction: The Ongoing Journey and Beyond

2026年2月10日(火) 10:00 - 12:00

Ciappina Marcelo (Professor, Guangdong Technion, China)

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

Finite-size effects on the QCD critical point

2026年2月9日(月) 15:30 - 17:30

Gyozo Kovacs (Research Fellow, Institute of Theoretical Physics, University of Wroclaw, Poland)

[Joint seminar hosted by QMS Team (iTHEMS) and FTR Team (R-CCS)] While effective approaches are important tools in the search for the QCD critical point, the physical systems they describe differ in several aspects from those in heavy-ion collisions and from unextrapolated lattice QCD. A primary discrepancy is the system size, which is infinite only in effective model calculations. Various implementations exist to account for the resulting finite-size effects. Beyond the frequently used methods, we present a comprehensive mean-field approach that allows for both infinite- and finite-size calculations, even within a complex parameter space. We discuss the general impact of finite-size effects on key observables, such as conserved charge fluctuations, and on the analytic structure of the thermodynamic potential. 15:30-16:30 Lecture 16:30-17:30 Discussion with coffee

会場: 研究本館 (メイン会場) / via Zoom

イベント公式言語: 英語

What can we learn from kilonovae about nucleosynthesis and high-density matter?

2026年2月9日(月) 14:00 - 15:15

オリバー・ユスト (Postdoctoral Researcher, GSI Helmholtzzentrum für Schwerionenforschung, Germany)

The electromagnetic transients accompanying neutron-star mergers (NSMs), called kilonovae, are powered by the radioactive decay of freshly synthesized heavy elements. As such they should contain rich information about the ejected matter and the properties of the extremely dense meta-stable neutron-star remnant formed right after the collision. However, extracting such information from observed kilonova light curves and spectra remains a challenging endeavor, which requires sophisticated models of various hydrodynamic processes and neutrino transport effects, detailed knowledge of nuclear and atomic physics, as well as complex radiative transfer calculations. In this talk I will report recent efforts from our "HeavyMetal" collaboration aimed at deciphering kilonovae.

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

Mathematical Application Research Team Meeting #12

2026年2月6日(金) 14:00 - 15:30

リッカルド・ムオロ (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)

Mathematical Application Research Team invites Riccardo Muolo fom Division of Fundamental Mathematical Science to this meeting. You are welcome to join the meeting. Title: Dynamics beyond nodes: a topological framework for oscillatory dynamics on higher-order networks Abstract: In recent years, increasing attention has been given to dynamical processes taking place on higher-order networks, where interactions are not limited to links, but may involve also higher-dimensional simplices [1]. While classical network models assume that state variables live on nodes and interact through links, many real systems — including brain, climate, and transportation systems — cannot be fully described within this node-centric perspective [2]. In this seminar, I will introduce the framework of higher-order networks and the concept of topological signals, namely, dynamical variables defined on simplices of higher dimensions. I will briefly present the basic tools required for this setting, including elementary notions of discrete calculus, discrete topology and geometric algebra, which serve as the mathematical foundation for modeling dynamical processes beyond the node-based paradigm. Next, I will discuss models of oscillatory dynamics extended to this framework. First, I will present the topological Kuramoto model [3], in which phases are not restricted to nodes but may also be associated with links, and where the coupling arises from the combinatorial structure of the simplicial complex. Then, I will introduce the discrete Hodge Laplacian and the Dirac-Bianconi operator [4], the former generalizing diffusive interactions to the higher-order setting, while the latter provides cross-talk between signals defined on simplices of different dimensions. Finally, I will introduce the notion of Dirac-Bianconi driven oscillators, where the dynamics of node- and link-signals coexist, interact and may give rise to collective oscillatory behaviors [5].

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

Quantitative characterization of microbial diversity and environmental adaptation

2026年2月5日(木) 13:00 - 14:30

松本 美緒 (理化学研究所 開拓研究所 (PRI) 鈴木地球・惑星生命科学研究室 大学院生リサーチ・アソシエイト)
鈴木 志野 (理化学研究所 開拓研究所 (PRI) 鈴木地球・惑星生命科学研究室 主任研究員)

イベント公式言語: 英語

Scalable Simulation of Quantum Many-Body Dynamics with Or-Represented Quantum Algebra

2026年2月4日(水) 14:30 - 16:00

Lukas Broers (理化学研究所 計算科学研究センター (R-CCS) 量子系物質科学研究チーム 特別研究員)

High-performance numerical methods are essential for advancing quantum many-body physics, as well as for enabling the integration of supercomputers with emerging quantum computing platforms. We have developed a scalable and general-purpose numerical framework for quantum simulations based on or-represented quantum algebra (ORQA). This framework applies to arbitrary spin-systems and naturally integrates with quantum circuit simulation in the Heisenberg picture, particularly relevant to recent large-scale experiments on superconducting qubit processors [Kim et al., Nature 618, 500 (2023)]. As a benchmark, we simulate the kicked Ising model on a 127-qubit heavy-hexagon lattice, successfully tracking the time-evolution of local magnetization using up to one trillion Pauli strings. Our simulations exhibit strong scaling up to 2^17 parallel processes with near-linear communication overhead. Further, we show that our framework is naturally extended to a broader range of quantum systems, superseding the capabilities of recently established Pauli propagation methods. We present possible future directions on how to utilize our algorithm.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

JST-Sakura Science Exchange Program: AI for Atmospheric Science

2026年2月4日(水) - 10日(火)

This JST-Sakura Science Exchange Program leverages the complementary strengths and research foundations of Fudan University and RIKEN in atmospheric science, focusing on the important scientific challenge of applying artificial intelligence to cloud remote sensing and data assimilation. The exchange program also includes one-day workshop in R-CCS with Data Assimilation Research Team.

会場: 融合連携イノベーション推進棟（IIB） (メイン会場) / via Zoom / RIKEN Center for Computational Science, 1F Seminar room

イベント公式言語: 英語

From Wavefunction Sparsity to Quantum Filter-Assisted Subspace Diagonalization

2026年2月4日(水) 13:00 - 14:30

Han Xu (理化学研究所 計算科学研究センター (R-CCS) 量子系物質科学研究チーム 特別研究員)

Subspace diagonalization techniques based on quantum sampling, such as quantum selected configuration interaction (QSCI) and sample-based quantum diagonalization (SQD), are a class of quantum-centric algorithms for approximating ground-state energies of many-body systems. One of the foundational bottlenecks for SQD is due to the lack of compactness of the ground-state wavefunctions. In this talk, we will introduce a filter-assisted SQD protocol that enhances the wavefunction sparsity through a quantum-circuit transformation of the Hamiltonian. Using the Gini coefficient as a robust sparsity measure, we clarify how sparsity determines the resource requirements of SQD. To construct the quantum filter, we develop a tensor-network-based automatic circuit-encoding algorithm that encodes the target matrix product states with controllable fidelity. We benchmark the method on the quantum Ising model under the transverse and longitudinal fields, using both numerical simulations and experiments on IBM quantum hardware. Our results show that the filter-assisted protocol reduces energy-estimation errors by orders of magnitude and substantially lowers the overhead of measurement compared with standard SQD, which highlight the potential of filter-assisted protocol in quantum-centric computing for strongly correlated materials.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語