iTHEMSセミナー

Disorder and Defects in Critical Systems

2026年6月8日(月) 13:30 - 15:00

Baishali Roy (Postdoctoral Fellow, Indian Institute of Technology Kanpur, India)

Real critical systems are often constrained by boundaries and affected by impurities. In 3d, the effect of disordered impurities on the boundary can be modeled by a random magnetic field on a two-dimensional defect. In this talk, I will discuss how such disorder affects the Wilson-Fisher fixed point in d=4−\epsilon dimensions. By analyzing the one-loop RG flow of the defect couplings using the replica formalism, we find a non-trivial "dirty" fixed point which represents a new boundary universality class, stabilized by the bulk \phi^4 interaction. Disordered systems at critical points are known to exhibit logarithmic behavior — I will also discuss how operator mixing in the replica limit gives rise to a logarithmic defect CFT in our setup.

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

Closed Seminar on Quantum Topology and Related Topics

2026年5月29日(金) 14:00 - 18:00

星野 真生 (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)
北村 侃 (立教大学 理学部 数学科 助教)
村上 友哉 (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)
ウアジーミャ・ソスニロ (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)

We will hold a closed seminar on quantum topology and related topics. The talks will be given by the following four speakers. The talks will not be streamed online or recorded. 14:00–14:30 Mao Hoshino 14:30–15:00 Kan Kitamura (15:00–15:30 Coffee break) 15:30–16:00 Yuya Murakami 16:00–16:30 Vladimir Sosnilo (16:30–17:30 Casual reception)

会場: セミナー室 (359号室)

イベント公式言語: 英語

Seeing Photons, from Einstein to Bohr to Hanbury Brown-Twiss and related Hong-Ou-Mandel Interference Phenomena

2026年4月22日(水) 15:00 - 16:30

ゴードン・ベイム (Professor Emeritus, University of Illinois, USA)

Why do we believe that the electromagnetic field is quantized, and photons exist? This talk will focus on two ways that the quantization of the electromagnetic field manifests itself in interference experiments. Bohr, who initially doubted photons after Einstein's initial proposal of the photon to explain the photoeffect, eventually proposed a thought experiment showing that the consistency of elementary quantum mechanics at the level of two slit diffraction requires the quantization of the electromagnetic field. In addition, as I will argue, both Hanbury Brown-Twiss interferometry and the closely related Hong-Ou-Mandel effect provide yet another way to see that the electromagnetic field must be quantized.

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

RIKEN Seminar: Formulation of Life Phenomena from Quantum Theory

2026年4月16日(木) 14:00 - 16:05

13:45 Opening 14:00-14:05 Introduction Atsushi Iriki (Teikyo University Advanced Comprehensive Research Organization Division of Artificial Intelligence, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) 14:05-14:35 "Interpretation of Life Phenomena Using Quantum Wave Functions and Field Theory" Kazuhiro Sakurada (Keio University Medical School and RIKEN Center for Integrative Medical Sciences (IMS), Predictive Medicine Special Project (PMSP)) 14:35-14:45 Q&A 14:45-15:30 "Bridging neurophysiology and quantum-like cognition" Andrei Khrennikov (Center for Mathematical Modeling in Physics and Cognitive Sciences Linnaeus University) 15:30-15:45 Q&A 15:45-16:00 "Quantum-Like Measurement" Masanao Ozawa (RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN TRIP FQSP, and Nagoya University) 16:00-16:05 Closing Remarks Satoshi Iso (Director, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)) Host Laboratory: Predictive Medicine Special Project, RIKEN Center for Integrative Medical Sciences (IMS) / RIKEN Center for Interdisciplinary Theoretical and Mathematical Science (iTHEMS) *Registration is required by April 14 via the registration form. Contact: Predictive Medicine Special Project (pmsp-web@ml.riken.jp)

会場: 理化学研究所 和光キャンパス 脳科学池の端研究棟（建物番号C56）3階305

イベント公式言語: 英語

The career talk: From Quarks to Cinematic Sparks

2026年2月27日(金) 15:00 - 16:30

Agnes Mocsy (Professor, Department of Mathematics and Science, Pratt Institute, USA)

While my career began in a linear way, it gradually opened into a non-traditional path through unexpected mergings, where theoretical nuclear physics, filmmaking, and creative public and academic engagement intertwined. I will share how scientific inquiry, artistic practice, and storytelling began shaping one another, opening new ways to explore complexity, emotion, and connection. Drawing on work from my physics research to cinema projects like Rare Connections, I will reflect on how curiosity and creative thinking move freely across science and art, deepening each and expanding how we understand the human experience. My aim is to offer a perspective on the possibilities that emerge when we allow our multitudes to meet and transform one another.

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

Higher Gauge Structures and Invariant Action Principles

2026年1月6日(火) 15:15 - 16:15

Sebastián Salgado (External Researcher, Instituto de Alta Investigacion, Universidad de Tarapaca, Chile)

I present the systematic construction of gauge theories based on free differential and L-infinity algebras. This provides a consistent algebraic framework for constructing gauge-invariant theories whose field content is extended by higher-degree differential forms as gauge potentials. I derive explicit expressions for the corresponding extended Chern-Simons actions and the generalized anomaly terms that emerge from them. Possible applications to gravity and supergravity will also be discussed.

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

Invitation to Random Tensor Models: from random geometry, enumeration of tensor invariants, to characteristic polynomials

2026年1月6日(火) 13:30 - 14:30

鳥海 玲子 (沖縄科学技術大学院大学 (OIST) 准教授)

I will introduce random tensor models by first reviewing their motivation coming from random geometric approach to quantum gravity. Then, I will selectively present some of the interesting research results, by highlighting recent results on enumeration of graphs representing tensor invariants, and reporting our recent work on a new notion of characteristic polynomials for tensors via Grassmann integrals and distributions of roots of random tensors. The latter two are based on arXiv:2404.16404[hep-th] and arXiv:2510.04068[math-ph]

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

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

2025年12月5日(金) 14:00 - 15:30

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.

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

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 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

Topology and Brain Science

2025年5月16日(金) 14:00 - 15:30

Shiu Gary (Professor, Department of Physics, University of Wisconsin-Madison, USA)

会場: via Zoom

イベント公式言語: 英語

Artificial Intelligence and Neuroscience

2025年4月11日(金) 14:00 - 15:30

近添 淳一 (広島大学 脳・こころ・感性科学研究センター 教授)

Recent advancements in artificial intelligence have led to various discoveries in the field of neuroscience. For example, it has been demonstrated that the information on orientation columns in the visual cortex and the basic taste information in the gustatory cortex can be extracted by applying machine learning to relatively low-resolution functional MRI data. Additionally, intriguing findings have emerged, such as the information processing structures of artificial neural circuits—designed independently of the brain—showing similarities to those of biological neural networks. In this talk, I will discuss the applications of artificial intelligence in neuroscience and explore future directions in this field.

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

Omega Meson from Lattice QCD

2025年4月2日(水) 15:00 - 16:00

Haobo Yan (Ph.D. Student, School of Physics, Peking University, China)

The three-body problem, renowned for its unsolvable nature in celestial mechanics and homonymous science fiction, is not only solvable in the quantum realm regarding spectra but also offers profound insights into QCD. In this talk, I will present the first-ever lattice calculation of the resonance parameters for the lightest hadron decaying into three particles, the -meson. By mapping finite-volume energy levels to infinite-volume scattering amplitude, a pole position trajectory is obtained that, when extrapolated to the physical point, shows good agreement with the experiment.

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

The puzzle of angular momentum conservation in beta decay and related processes.

2025年3月21日(金) 14:00 - 15:30

ゴードン・ベイム (Professor Emeritus, University of Illinois, USA)

This is a iTHEMS-FQSP joint seminar. We ask the question of how angular momentum is conserved in a number of related processes, from elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon; to scattering of a fully relativistic spin-1/2 particle by a central potential; to inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus, where the final spin is in a different direction than that of the neutrino – an apparent change of angular momentum. The apparent non-conservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in direction in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

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

iTHEMS - Nishina Center Joint Seminar: The Golden Age of Neutron Stars

2025年3月17日(月) 15:30 - 17:00

ゴードン・ベイム (Professor Emeritus, University of Illinois, USA)

This is a iTHEMS - Nishina Center Joint Seminar. Neutron stars were first posited in the early thirties, and discovered as pulsars in the late sixties; however we are only recently beginning to understand the matter they contain. After touching briefly on the history of neutron stars, I will describe the ongoing development of a consistent picture of the liquid interiors of neutron stars, now driven by ever increasing observations as well as theoretical advances. These include, in particular. observations of at least three heavy neutron stars of about 2.0 solar masses and higher; ongoing simultaneous inferences of masses and radii of neutron stars by the NICER telescope; and past and future observations of binary neutron star mergers, through gravitational waves as well as across the electromagnetic spectrum. I will also discuss pulsar timing arrays to detect very long wavelength gravitational waves, a remarkable role for neutron stars. Theoretically an understanding is emerging in QCD of how nuclear matter can turn into deconfined quark matter in the interior, and be capable of supporting heavy neutron stars, which I will illustrate with a discussion of modern quark-hadron crossover equations of state.

会場: RIBF棟 2階 大会議室 (メイン会場) / via Zoom

イベント公式言語: 英語

Applications of Geometry of Numbers to Phyllotaxis and Crystallography

2025年2月28日(金) 14:00 - 15:30

富安 亮子 (九州大学 マス・フォア・インダストリ研究所 教授)

The golden angle method, originally known from phyllotaxis in botany, has been used to generate dense point packings on surfaces of revolution. In my recent work, I have extended this method to general surfaces and higher-dimensional manifolds by employing the theories of products of linear forms in number theory, diagonalizable metrics in differential geometry, and local solutions of quasilinear hyperbolic equations. This extension suggests that any biological forms can exhibit phyllotactic patterns locally regardless of their morphology, while the overall pattern is influenced by their global properties in the embedded space. On the algebraic side, it is interesting that the same ideas used for phyllotaxis can also be applied to pseudorandom number generation over F2 = {0, 1}. This work is motivated by my previous research in crystallography. Time permitting, I will also introduce some of the research, which contributes to the analytical foundations of crystallography and is also an application of the geometry of numbers.

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

Mathematical Studies on Human Cooperation

2025年2月12日(水) 15:00 - 17:00

村瀬 洋介 (理化学研究所 計算科学研究センター (R-CCS) 離散事象シミュレーション研究チーム 研究員)

Cooperation is a fundamental part of human society. But from an evolutionary perspective, it remains a puzzle—why do people help others even when it costs them? In theory, selfish individuals should have an advantage over cooperators. To explain how cooperative behaviors evolved, researchers have proposed several mechanisms, among which direct and indirect reciprocity play key roles in human interactions. In this talk, I will present my research on the evolution of cooperation, focusing on these two mechanisms. I will begin with an introduction to game theory and evolutionary game theory, which help us understand how people make decisions in strategic situations. Then, I will discuss my study on the repeated Prisoner’s Dilemma, where we discovered a new class of strategies through mathematical analysis and large-scale computations [1]. Finally, I will talk about my research on indirect reciprocity, a process where people cooperate based on reputation [2].

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