セミナー

Optimal transport: Thermodynamics, biological information processing and generative models

2027年1月18日(月) 13:30 - 15:00

伊藤 創祐 (東京大学 大学院理学系研究科 准教授)

This is a joint seminar co-hosted by Institute for Physics of Intelligence (iπ), UTokyo, and the Venue is #1042,10F of Science Bldg.1 Optimal transport theory is a useful theoretical framework for geometrically characterizing the distance between probability distributions. It is not only used in recent research on generative models but has also been applied to detect information-processing capabilities in biological systems from a statistical perspective, and to discuss thermodynamic efficiency. In this seminar, I will begin with an introduction to optimal transport theory, and also discuss our research on its various applications. More specifically, I will discuss the following topics: 1) The problem of minimizing entropy production within a finite time and its experimental testing. 2) The application of optimal transport to the training of generative models, specifically diffusion models, and their optimal protocols. 3) Quantifying information processing performance using optimal transport in biological signal transduction.

会場: 東京大学 本郷キャンパス 理学部１号館 (メイン会場) / via Zoom

イベント公式言語: 英語

Hamiltonian simulation: Standard algorithms and recent developments

2026年12月17日(木) 10:30 - 17:00

水田 郁 (大阪大学 量子情報・量子生命研究センター 准教授)

This is a lecture-style seminar of quantum computation. The tentative schedule consists of three slots: 10:30-12:00, 13:30-15:00, and 15:30-17:00. Due to equipment limitations, the blackboard might not be visible on Zoom, so we recommend attending in person.

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

Chiral Anomaly, Neutral-Pion Lifetime and Axion–Photon Coupling

2026年12月7日(月) 15:00 - 16:30

Xu Feng (Professor, Director, Institute of Theoretical Physics, School of Physics, Peking University, China)

The chiral anomaly provides one of the rare opportunities to test QCD in the confinement regime at the percent level and beyond. A prime example is the neutral pion lifetime: after two decades of PrimEx measurements reaching 1.5% precision, future experiments at an upgraded 22 GeV JLab aim at the sub-percent level, calling for a comparably precise first-principles QCD prediction. The same anomaly also governs the QCD contribution to the axion–photon coupling, a key quantity connecting axion models to experimental searches for one of the leading dark-matter candidates. In this talk, I will present our recent lattice QCD studies of these two quantities, going beyond the chiral limit.

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

Quantum Geometry from Matrices: Framework and Applications

2026年11月30日(月) 15:00 - 16:30

Harold Steinacker (Senior Scientist, Faculty of Physics, University of Vienna, Austria)

I will discuss the general framework of matrix geometry, which is a version of quantum geometry defined by a set of almost-commuting matrices. This framework allows for an efficient description of manifolds embedded in some target or feature space, which is particularly efficient for high-dimensional manifolds. I will discuss some applications in data science as well as in fundamental physics, notably how spacetime and gravity can emerge from the IKKT or IIB matrix model in this framework.

会場: 研究本館 3階 359号室とZoomのハイブリッド開催 / via Zoom

イベント公式言語: 英語

Rare k-mers reveal centromere haplogroups underlying human diversity and cancer translocation

2026年11月26日(木) 13:00 - 14:00

白石 友一 (国立がん研究センター研究所 ゲノム解析基盤開発分野 分野長)

Centromeres are highly variable and rapidly evolving regions of the human genome, and are frequently implicated in various cancers. Human centromeres consist of highly repetitive DNA sequences known as α-satellite higher-order repeats (HORs), which makes their analysis using conventional genome sequencing approaches extremely challenging. Although long-read sequencing technologies now enable near-complete sequencing of centromeres, applying these methods to large numbers of samples remains difficult. As a result, our understanding of centromere diversity across populations and its role in chromosomal rearrangements in cancer has remained limited. In this study, by focusing on rare k-mer markers, we demonstrate that α-satellite HOR haplotypes cluster into genetically related haplogroups. We further developed a software tool, ascairn, to accurately infer these haplogroups from common short-read whole-genome sequencing (WGS) data. Applying our approach to a dataset of more than 3,300 human samples revealed extensive centromere diversity and geographic variation. We also applied the rare k-mer–based approach to centromere sequences from 104 Japanese individuals generated as part of the Japanese Pangenome Project. This analysis revealed characteristic patterns of centromere evolution in the Japanese population and provided new insights into Japanese-specific centromere variation. In addition, we used this method to investigate class-defining chromosomal translocations, specifically der(1;19), also known as 1p/19q co-deletion, in oligodendrogliomas. By analyzing 142 samples from TCGA, we hypothesized that the breakpoints occurred on the p-arm side of D1Z7 and the q-arm side of D19Z3. This hypothesis was subsequently validated through extensive long-read sequencing in two cases, indicating that der(1;19) results in a dicentric chromosome containing two functional centromeres. We also observed that chromosomal rearrangements preferentially occurred in haplotypes with longer repetitive arrays on either the q-arm or p-arm side of the centromere. Furthermore, we identified specific centromere haplogroups associated with either increased or decreased likelihoods of der(1;19) translocations. Our findings show that rare k-mer analysis is a powerful approach for investigating centromere complexity and clarifying the mechanisms underlying centromere-associated abnormalities in cancer.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Quantum Simulation of Non-Equilibrium Dynamics in SU(2) and SU(3) Lattice Gauge Theories

2026年11月24日(火) 15:00 - 16:30

Xiaojun Yao (Research Assistant Professor, University of Washington, USA)

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

Real-time calculations for excited state tunneling

2026年11月17日(火) 14:00 - 15:30

Thomas Steingasser (Postdoctoral Fellow, Institute of Theoretical Physics (IFT), Spain)

Quantum tunnelling is conventionally formulated through Euclidean instantons, obscuring the role of physical time and complicating non-vacuum initial states. I will review the steadyon picture, in which infinitesimally regulated real-time path integrals are controlled by complex saddles whose projections recover familiar instantons. I will summarize its applications to finite-temperature decay, resonance states and states carrying conserved Noether charge, highlighting an emerging unified description of tunnelling beyond the false vacuum.

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 / via Zoom

イベント公式言語: 英語

A non-negative matrix factorization-based approach to integrating multimodal omics data with automatically tuned hyperparameters

2026年11月16日(月) 14:00 - 15:00

ドロシー・エリス (理化学研究所 生命医科学研究センター (IMS) 統合ゲノミクス研究チーム 特別研究員)

会場: via Zoom

イベント公式言語: 英語

Topological properties of empirical fitness landscapes from merge trees

2026年11月9日(月) 13:00 - 14:00

Igors Dubanevics (沖縄科学技術大学院大学 (OIST) 博士課程)

How evolution navigates sequence space depends on the shape of the fitness landscape. Viewed as a scalar field over a discrete genotype graph, theoretical landscapes range from single-peaked to rugged and fragmented, with very different mutational accessibility. Which shapes real biological sequences occupy remains an open empirical question. Deep mutational scanning now measures sequence–function maps across complete combinatorial regions of sequence space, but the resulting landscapes are large, noisy, and hard to compare across studies. Existing analyses typically reduce each dataset to a few summary statistics, discarding which peaks connect to which, and through which saddles. We are developing a two-layer toolkit for empirical sequence–function landscapes. A statistical layer models overdispersed sequencing counts directly to separate genuine phenotypic differences from measurement noise, pruning spurious topological features before analysis. A topological layer then summarises the landscape as a merge tree of peaks, saddles, and the high-fitness ridges that link them, using persistence as a natural scale to distinguish global structure from minor ruggedness. I will first illustrate this approach on the largest published combinatorially complete protein-coding landscape, spanning over 260,000 sequences. Filtering by measurement uncertainty and persistence simplifies an apparently rugged surface, revealing that major peaks remain connected through high-fitness saddles rather than isolated by deep valleys. I will then present preliminary findings from a comparative atlas of more than 150 combinatorially complete sequence–function landscapes spanning DNA, RNA, and protein. By comparing merge-tree structure across this collection, we ask whether high-fitness ridges that bypass rugged regions recur across unrelated sequences, and whether landscapes group by the biological function they encode.

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

Explaining GRB features through MAD black hole spin-down

2026年11月6日(金) 14:00 - 15:00

Aleksander Lenart (Ph.D. Student, Astronomical Observatory, Jagiellonian University, Poland)

Recent developments in numerical general relativity magnetohydrodynamics have shown that a fast-spinning black hole (BH) surrounded by a magnetically arrested disk (MAD) will lose its angular momentum due to jet energy extraction. The magnetic field in the disk causes turbulence, which significantly lowers the specific angular momentum of the matter. Therefore, the energy extraction dominates over angular momentum delivery, and the BH loses its spin. In a recent paper by my team, we applied those findings to the data of Gamma-ray Bursts (GRBs). Those sources are primarily produced in the high-mass star core-collapse, resulting in the creation of a compact central object like a BH or a magnetar. Some GRBs exhibit an extreme energy budget of>10^53 erg, which is above the maximum possible energy of a magnetar. Therefore, for some sources, the BH-powered emission is the only known mechanism that could explain observations. I will demonstrate how such a scenario allows us to model GRB light curves, and how it predicts the Dainotti correlation. The anti-correlation between the duration of the plateau phase in the light curve and its luminosity. I will discuss the typical masses of BHs that could have been created in GRB events and the possible connection with the gravitational wave observations.

会場: 研究本館 2階　220号室 / via Zoom

イベント公式言語: 英語

Scaling regimes of the 1D Kuramoto-Sivashinsky equation

2026年11月5日(木) 17:00 - 18:30

Liubov Gosteva (Ph.D. Student, LPMMC, Université Grenoble Alpes, France)

The Kuramoto-Sivashinsky (KS) equation describes various phenomena exhibiting chaos and instabilities, including flames, reaction-diffusion processes, and thin liquid film flows. It resembles the Kardar-Parisi-Zhang (KPZ) equation, with the key difference being the negative "viscosity" in the KS equation. The KS equation is known to belong to the KPZ universality class: at large scales, its statistical properties are governed by the KPZ fixed point, characterized by the dynamical exponent $z=3/2$ and a known PDF of fluctuations. In this talk, I will analyze the stochastic KS equation using the functional renormalization group (FRG). In this framework, attractive fixed points of the FRG equation determine large-scale universal behavior, while unstable fixed points govern small-scale universal behavior. I will show that the two-point correlation function exhibits, besides the KPZ scaling at large scale, another universal scaling regime at small scale, with $z=1$. This scaling is very robust as it is intrinsic to the KS dynamics. It arises from the vanishing of the effective viscosity when evolving from its microscopic negative KS value, to its macroscopic effective positive KPZ value. I will also present results from direct numerical simulations, which confirm these findings.

会場: via Zoom

イベント公式言語: 英語

Quantum Creation of the Universe: Reassessing the No-Boundary and Tunneling Proposals

2026年10月30日(金) 14:00 - 15:00

松井 宏樹 (大阪公立大学 数学研究所 特別研究員)

How was our Universe created? This is one of the most fundamental questions in cosmology. Quantum cosmology attempts to answer it by using a "wave function of the Universe," and for four decades the discussion has been dominated by two proposals: the no-boundary proposal of Hartle and Hawking, and the tunneling proposal of Vilenkin. The two predict very different initial states for our Universe, yet for a long time there was no common framework in which they could be exactly analyzed and compared. In this talk I will begin with a pedagogical introduction to the wave function of the Universe and to the Lorentzian path integral formulation based on Picard-Lefschetz theory, which makes the gravitational path integral well defined without the ambiguities of the traditional Euclidean approach and allows both proposals to be treated on the same footing. I will then present our recent results. Using Lefschetz-thimble analysis together with resurgence theory, we resolve the Stokes-line ambiguity that had obscured earlier analyses and show that the path integral uniquely yields the tunneling wave function rather than the no-boundary one. The no-boundary saddles nevertheless leave a trace: their contributions exactly cancel the Borel ambiguity of the perturbative quantum-gravity corrections around the tunneling saddle, demonstrating that resurgence is at work in quantum cosmology. I will also discuss quantum cosmology beyond four-dimensional general relativity, using two-dimensional Jackiw-Teitelboim gravity as an illustrative model.

会場: 研究本館 3階 359号室とZoomのハイブリッド開催 / via Zoom

イベント公式言語: 英語

Maximal Enhancements in Eight-Dimensional Non-Supersymmetric Heterotic Strings

2026年10月30日(金) 10:30 - 12:00

Yuefeng Liu (九州大学 高等研究院 学術研究員)

We classify maximally enhanced, rank-preserving non-supersymmetric heterotic strings in eight dimensions by studying orbifolds of supersymmetric heterotic strings on T^2.We first review the construction in nine dimensions, where it reproduces the 95 maximally semisimple enhancement points obtained from previous extended-Dynkin analyses. We then start from the maximally enhanced supersymmetric Narain points in eight dimensions and use Kac's theorem to enumerate candidate order-two inner actions, retaining only those that lift to consistent Narain-lattice shifts. This gives 1210 maximal enhancement points, of which 71 are tachyon-free, and 25 have neither tachyons nor shifted-sector massless scalars. For each entry we determine the gauge algebra and the low-lying scalar and fermion spectra, and for the tachyon-free cases we evaluate the one-loop cosmological constant. For the 25 subcases without shifted-sector massless scalars, we further compute the Hessian of the one-loop potential and test the refined de Sitter swampland conjecture.

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

Behaviorally Informed Institutional Design with Game Theory and LLMs

2026年10月29日(木) 14:30 - 15:30

森 隆太郎 (理化学研究所 脳神経科学研究センター (CBS) 計算論的集団力学連携ユニット 基礎科学特別研究員)

The event will start 30 minutes before initially announced. How can we design social institutions that account for how people actually make decisions? Behavioral research has revealed substantial heterogeneity in preferences and decision-making that traditional economic models often abstract away. Understanding these tendencies may open new possibilities for improving collective outcomes. In this talk, I present two projects addressing complementary aspects of this broader goal. First, I investigate how real-time interaction facilitates cooperation in a one-shot social dilemma, where purely self-interested behavior predicts only mutual defection. Experiments show that real-time interaction yields higher mutual cooperation, primarily through stronger reciprocity by followers. A game-theoretic model suggests that flexible decision timing helps people infer others' cooperative preferences from their actions and coordinate their responses. This illustrates how institutional tweaks can leverage existing cooperative tendencies. Second, I introduce Cross-Centaur, an LLM-based model of individual decision-making across diverse domains. We construct a dataset in which the same participants complete tasks spanning learning, decisions under risk and delay, reasoning, and social decision-making, and use it to fine-tune an LLM. The model uses behavior in one task to better predict the same individual's decisions in another, a step toward more flexible, generalizable models of decision-making. Together, these projects explore how understanding human decision-making may inform the design of better social institutions.

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 / via Zoom

イベント公式言語: 英語

Towards the Geometric Beauty of Bonsai

2026年10月29日(木) 13:00 - 14:00

内海 忍 (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 学振特別研究員PD)

I will present an overview of my ongoing and future research projects. Art has been a central element of human culture and society across regions and throughout history. However, the inherent subjectivity of aesthetic evaluation has long made it challenging to study art quantitatively and systematically within the mathematical sciences. My research tackles this challenge through bonsai—the art of recreating the grandeur of natural landscapes and majestic trees within a small pot. Often described as a “living art” and a “crystallization of Japanese aesthetics,” bonsai provides a unique opportunity to explore a fundamental question: How can we quantify something as seemingly subjective as beauty? The key methodology of this research involves the 3D digitization of actual bonsai using photogrammetry, followed by the extraction of their skeletal structures and their representation as 3D non-looped tree graphs. I then apply morphological and network analyses to investigate commonalities and differences in branching structures across bonsai of different styles and grades. Looking ahead, I will discuss future research directions, including how these analyses and mathematical models could be extended to quantitatively characterize traditional Japanese aesthetic principles (e.g., the beauty of subtraction and negative space), as well as what distinguishes the structures of artistically cultivated bonsai from those of naturally growing trees.

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 / via Zoom

イベント公式言語: 英語

Exploring Noisy Quantum Thermodynamical Processes via the Depolarizing-Channel Approximation

2026年10月28日(水) 16:00 - 17:00

Jian Li (Ph.D. Student, Center for Theoretical Physics, Polish Academy of Sciences, Poland)

Noise and errors are unavoidable in any realistic quantum process, including processes designed to reduce noise and errors in the first place. In particular, quantum thermodynamical protocols for cooling can be significantly affected, potentially altering both their performance and efficiency. Analytically characterizing the impact of such errors becomes increasingly challenging as the system size grows, particularly in deep quantum circuits where noise can accumulate in complex ways. To address this, we introduce a general framework for approximating the cumulative effect of gate-dependent noise using a global depolarizing channel. We specify the regime in which this approximation provides a reliable description of the noisy dynamics. Applying our framework to the thermodynamical two-sort algorithmic cooling (TSAC) protocol, we analytically derive its asymptotic cooling limit in the presence of noise. Using the cooling limit, the optimal cooling performance is achieved by a finite number of qubits --- distinguished from the conventional noiseless TSAC protocol by an infinite number of qubits --- and fundamental bounds on the achievable ground-state population are derived. This approach opens new avenues for exploring noisy quantum thermodynamical processes.

会場: via Zoom

イベント公式言語: 英語