第28回 MACSコロキウム・2025年度MACS学生説明会

2025年4月25日(金) 14:45 - 18:30

鍛冶 静雄 (九州大学 マス・フォア・インダストリ研究所 教授 / 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) 教授)

14:45-15:00 ティータイムディスカッション 15:00-16:00 鍛冶 静雄（九州大学マス・フォア・インダストリ研究所 教授／京都大学理学研究科附属サイエンス連携探索センター 教授）「折り紙にひそむ数学：カライドサイクルの幾何学」 16:15-17:20 2024年度MACS学生説明会 17:30-18:30 継続討論会

会場: 京都大学 理学研究科セミナーハウス（建物配置図（北部構内）【10】の建物）

イベント公式言語: 日本語

Insights on Issues in the Cold Dark Matter Hypothesis

2025年4月25日(金) 14:00 - 15:15

Yuka Kaneda (筑波大学 数理物質科学研究群 物理学学位プログラム 博士課程)

Dark matter accounts for 85% of the matter component of our universe, but its true nature is still unclear. The Lambda-Cold Dark Matter (CDM) model, which thought to be the standard model, reproduces well the statistical properties of the large-scale structure of our universe. However, at the scale of galaxies and dwarf galaxies, serious discrepancies between the predictions of the CDM model and observations have been pointed out. In this study, we tackle on the “cusp-core problem” and the “missing satellite problem,” which are typical examples of such discrepancies, using N-body simulations. In the talk, the physical trigger of cusp-to-core transition and the novel method to find missed satellites are presented.

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

Asymptotic Waves in Stars

2025年4月23日(水) 14:00 - 15:30

Jim Fuller (Professor, Division of Physics, Mathematics, and Astronomy (TAPIR), California Institute of Technology (Caltech), USA)

Waves propagating through stars often have very short wavelengths in the radial direction, enabling WKB approximations that facilitate understanding. The main types of waves that propagate in stars are acoustic waves (restored by pressure forces) and gravity waves (restored by buoyancy forces). I will also discuss how the properties of these waves are changed by rotation (adding Coriolis and centrifugal forces) and magnetic fields (adding Lorentz forces). Finally, I will discuss how these waves carry energy and angular momentum through stars, and discuss some potential consequences for stellar evolution.

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

On IR/UV divergence of inflationary decoherence

2025年4月22日(火) 14:00 - 15:30

佐野 文哉 (東京科学大学 博士課程)

Supported by observational evidence indicating that cosmological scalar perturbations were nearly Gaussian at the beginning of the universe, it is anticipated that the origin of these perturbations is quantum fluctuations. Consequently, cosmic inflation provides a valuable laboratory for testing the quantum nature with/of gravity. Evaluation of the quantumness of the primordial perturbations is an inevitable step for the purpose. However, quantum states of the perturbations are suffered from IR/UV divergence, resulting in fully classical states. In this presentation, I will first review the evaluation of the quantum coherence in de Sitter spacetime as a measure of quantumness, and then show how to regularize the divergence.

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

iTHEMS × academist オンラインイベント「数理で読み解く科学の世界 2025」

2025年4月19日(土) 10:00 - 15:30

金久保 優花 (理化学研究所 数理創造研究センター (iTHEMS) 国内外連携・人材育成部門 理研バークレーセンター 特別研究員)
北村 侃 (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)
シュパイデル 玲雄 (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 理研ECL研究ユニットリーダー)
横倉 祐貴 (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)

「数理で読み解く科学の世界」は、2020年より毎年4月に開催しているオンラインイベントです。主催のiTHEMSは、「数学」を共通言語として、物理、生物、宇宙などさまざまな科学分野の横断的な研究をしており、イベントでは、iTHEMS所属の若手研究者4名が最先端の研究について中学生や高校生にもわかるように30分程度の講演を行います。また、一般参加者からの質問やコメントを受け付ける時間も設けています。 詳細、参加お申し込みは、関連リンクをご覧ください。 日時：2025年4月19日（土）10:00〜15:30（開場 9:45） 場所：Web会議サービス「Zoom」（申込者に事前に招待URLをお伝えいたします） 参加費：無料 対象者：中学生・高校生、社会人（どなたでもご参加いただけます） 主催：iTHEMS 共催（企画・運営・宣伝）：アカデミスト株式会社 特別協力：NPO法人 数理の翼 タイムスケジュール： 10:00～　開始の挨拶・イベント概要説明 10:15～　講演「太陽より熱いスープ - クォーク・グルーオン・プラズマのレシピ」金久保 優花 博士 11:15～　講演「数、形、対称性」北村 侃 博士 12:10～　昼休み企画　「数学者と物理学者が語る！これからの数理の未来」 13:05～　講演「数理と遺伝情報で紐解く人類史」シュパイデル 玲雄 博士 14:05～　講演「ブラックホールは情報の玉手箱？」横倉 祐貴 博士 15:00〜　アフタートーク 15:30　　終了予定

会場: via Zoom

イベント公式言語: 日本語

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

iTHEMS Biology Study Group April Launch Meeting (Part 2)

2025年4月10日(木) 13:00 - 14:00

Let's launch our Biology Study Group activities for the new year (Part 2 of 2). This meeting will be used to (1) say welcome to new member (SPDR Kenji Okubo, and Postdoc Lucas Sort); (2) discuss Biology seminar management in light of the new iTHEMS Centre; and (3) catch up on each other's current research. Since this will probably take us 2h, this will be Part 2 of 2 (Part 1 was on 4/3). On 4/10 (Part 2) we will get a 15 min introduction talk by Postdoc Lucas Sort. This meeting is open to all RIKEN and guests. You do not need to be a member of the iTHEMS Biology Study Group.

会場: via Zoom / 研究本館 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 Strategy for Proving the Strong Eigenstate Thermalization Hypothesis: Chaotic Systems and Holography

2025年4月3日(木) 16:00 - 17:00

川本 大志 (京都大学 基礎物理学研究所 博士課程／日本学術振興会 特別研究員 DC)

The strong eigenstate thermalization hypothesis (ETH) provides a sufficient condition for thermalization and equilibration. Although it is expected to hold in a wide class of highly chaotic theories, there are only a few analytic examples demonstrating the strong ETH in special cases, often through methods related to integrability. In this talk, I will explore sufficient conditions for the strong ETH that may apply to a broad range of chaotic theories. These conditions are expressed as inequalities involving the long-time averages of real-time thermal correlators. Specifically, I will discuss bottom-up holographic models that satisfy these conditions under certain assumptions, which are expected to hold in such models. This talk is based on the preprint 2411.09746 [hep-th].

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

Gauge subtleties and the finiteness of loop corrections beyond slow roll

2025年4月3日(木) 14:00 - 15:30

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)

The early universe undergoes a phase of exponential expansion called inflation, under which quantum fluctuations are amplified and later seed cosmological structures. A long-standing question is whether interactions of these quantum fields may significantly affect the n-point statistics of cosmological observables. These corrections are known as loop corrections. Recently, Kristiano and Yokoyama claimed that, in scenarios beyond slow-roll inflation, the one-loop correction of super-Hubble fluctuations could become non-negligible and violate cosmological-perturbation theory. This result is highly debated, and in this talk we will use a non-linear approach known as delta N formalism to evaluate these loop corrections. We find the existence of loop corrections for modes close to the Hubble scale, however, these corrections are quickly suppressed for long-wavelength modes. We also show how the result of Kristiano and Yokoyama may arise when truncating the perturbative expansion, and how this result depends on the chosen gauge.

会場: セミナー室 (359号室)

イベント公式言語: 英語

iTHEMS Biology Study Group April Launch Meeting (Part 1)

2025年4月3日(木) 14:00 - 15:00

Let's launch our Biology Study Group activities for the new year (Part 1 of 2). This meeting will be used to (1) say welcome to new member (SPDR Kenji Okubo, and Postdoc Lucas Sort); (2) discuss Biology seminar management in light of the new iTHEMS Centre; and (3) catch up on each other's current research. Since this will probably take us 2h, this will be Part 1 of 2 (Part 2 on 4/10). On 4/3 (Part 1) we will get a 15 min introduction talk by SPDR Kenji Okubo. This meeting is open to all RIKEN and guests. You do not need to be a member of the iTHEMS Biology Study Group.

会場: via Zoom / 研究本館 4階 共有スペース

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 rarer-sex effect

2025年3月27日(木) 16:00 - 17:00

Andy Gardner (Professor, School of Biology, University of St Andrews, UK)

The study of sex allocation—that is, the investment of resources into male versus female reproductive effort—yields among the best quantitative evidence for Darwinian adaptation, and has long enjoyed a tight and productive interplay of theoretical and empirical research. The fitness consequences of an individual's sex allocation decisions depend crucially upon the sex allocation behaviour of others and, accordingly, sex allocation is readily conceptualized in terms of an evolutionary game. I will discuss the historical development of understanding of a fundamental driver of the evolution of sex allocation—the rarer-sex effect—from its inception in the writing of Charles Darwin in 1871 through to its explicit framing in terms of consanguinity and reproductive value by William D. Hamilton in 1972. I will show that step-wise development of theory proceeded through refinements in the conceptualization of the strategy set, the payoff function and the unbeatable strategy.

会場: 研究本館 4階 445-447号室 (Hybrid) / via Zoom

イベント公式言語: 英語

Stability of nonsingular black holes

2025年3月27日(木) 15:00 - 16:30

辻川 信二 (早稲田大学 理工学術院 先進理工学研究科 物理学及応用物理学専攻 辻川研究室 教授)

We show that nonsingular black holes (BHs) realized in nonlinear electrodynamics are always prone to Laplacian instability around the center because of a negative squared sound speed in the angular direction. This is the case for both electric and magnetic BHs, where the instability of one of the vector-field perturbations leads to enhancing a dynamical gravitational perturbation in the even-parity sector. Thus, the background regular metric is no longer maintained in a steady state. We also generalize our analysis to the case in which a scalar field is present besides the U(1) gauge field and find no explicit examples of linearly stable nonsingular BHs. Our results suggest that the construction of regular BHs without instabilities is generally challenging within the scheme of classical field theories.

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

Third Workshop on Density Functional Theory: Fundamentals, Developments, and Applications (DFT2025)

2025年3月25日(火) - 27日(木)

The density functional theory (DFT) is one of the powerful methods to solve quantum many-body problems, which, in principle, gives the exact energy and density of the ground state. The accuracy of DFT is, in practice, determined by the accuracy of an energy density functional (EDF) since the exact EDF is still unknown. Currently, DFT has been used in many communities, including nuclear physics, quantum chemistry, and condensed matter physics, while the fundamental study of DFT, such as the first principle derivations of an accurate EDF and methods to calculate many observables from obtained densities and excited states, is still ongoing. However, there has been little opportunity to have interdisciplinary communication. On December 2022, we had the first workshop on this series (DFT2022) at Yukawa Institute for Theoretical Physics, Kyoto University, and several interdisciplinary discussions and collaborations were started. On February 2024, we had the second workshop on this series (DFT2024) at RIKEN Kobe Campus, and more stimulated discussion occured. To keep and extend collaborations, we organize the third workshop. Since the third workshop, we extend the scope of the workshop to the development and application of DFT as well. In this workshop, the current status and issues of each discipline will be shared towards solving these problems by meeting together among researchers in mathematics, nuclear physics, quantum chemistry, and condensed matter physics. This workshop mainly comprises lectures/seminars on cutting-edge topics and discussion, while sessions composed of contributed talks are also planned.

会場: 融合連携イノベーション推進棟（IIB） 8階 / via Zoom

イベント公式言語: 英語

A Century of Quantum Mechanics

2025年3月24日(月) 14:00 - 15:30

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

This is a RIKEN iTHEMS - The Univ. of Tokyo, Phys. Dept. Joint Seminar. This year, 2025, the "International Year of Quantum Science and Technology (IYQ)," is the 100th anniversary of the "formal" start of quantum mechanics, the description of the microscopic world. 1925 is the year in which Werner Heisenberg and others formulated "matrix mechanics," and physicists began to understand how to accurately predict microscopic phenomena. In this talk I will describe how quantum mechanics came about, starting with physicists in the late nineteenth century trying to understand the colors of hot metals and other hot objects, noting crucial advances leading to the fully developed wave and matrix quantum mechanics in the mid 1920's, to steps towards understanding real materials, culminating with spectacular applications such as smartphones, scarcely a century later.

会場: 東京大学 理学部4号館 1220号室 (メイン会場) / via Zoom

イベント公式言語: 英語

Fast radio bursts as precursor radio emission from monster shocks

2025年3月21日(金) 16:00 - 17:15

Arno Vanthieghem (Assistant Professor, Observatoire de Paris and Sorbonne Université, France)

It has been proposed recently that the breaking of MHD waves in the inner magnetosphere of strongly magnetized neutron stars can power different types of high-energy transients. Motivated by these considerations, we study the steepening and dissipation of a strongly magnetized fast magnetosonic wave propagating in a declining background magnetic field, by means of particle-in-cell simulations that encompass MHD scales. Our analysis confirms the formation of a monster shock, that dissipates about half of the fast magnetosonic wave energy. It also reveals, for the first time, the generation of a high-frequency precursor wave by a synchrotron maser instability at the monster shock front, carrying a fraction of 0.1% of the total energy dissipated at the shock. The spectrum of the precursor wave exhibits several sharp harmonic peaks, with frequencies in the GHz band under conditions anticipated in magnetars. Such signals may appear as fast radio bursts.

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 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