セミナー

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

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

Can we infer probability distributions from cumulants? Probabilistic approaches to inverse problems

2025年3月18日(火) 15:30 - 16:30

Yang-Yang Tan (Ph.D. Candidate, Dalian University of Technology, China)

Inverse problems, which involve estimating system inputs from outputs, are prevalent across science and engineering. Their ill-posed nature often makes finding numerically stable and unique solutions challenging. This seminar explores probabilistic methods for reconstructing distributions from a finite set of their moments or cumulants. We apply the Maximum Entropy Method (MEM) and Gaussian Process (GP) to reconstruct net-baryon number distributions across the QCD chiral crossover region using cumulant data from the STAR experiment and functional renormalization group (fRG) calculations. Our results demonstrate how higher-order cumulants shape distribution tails, while anomalous features in the reconstructed distributions provide constraints on the input cumulants. We also discuss deep learning approaches for distribution reconstruction from cumulants and present our recent work on physics-informed neural networks (PINNs) for solving fRG equations.

会場: via Zoom

イベント公式言語: 英語

Impact of the relativistic Cowling approximation on shear and interface modes of neutron stars

2025年3月18日(火) 11:00 - 12:30

Christian Kruger (Postdoctoral Researcher, University of Tuebingen, Germany)

Neutron stars are amongst the most compact objects known in the universe, which, therefore, require General Relativity for an accurate description. Seismic excitations of these stars may encode information about their currently unknown internal composition. As General Relativity is a mathematically complex theory, such oscillations are often considered in the Cowling approximation in which the spacetime is assumed to be static. In this talk, we will focus on shear and interface modes of neutron stars related to an elastic crust and investigate the impact of the Cowling approximation; we find that its impact on shear modes is negligible, while interface modes seem to experience some modification. Furthermore, we extend a scheme based on properties of Breit-Wigner resonances that allows to estimate the damping times of slowly damped modes. The proposed scheme is numerically robust and we compare it to estimates employing the quadrupole formula.

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

Asymptotically flat black hole spacetimes with multiple injections

2025年3月14日(金) 15:30 - 17:00

齊藤 佑太 (日本大学 大学院理工学研究科 物理学専攻 博士課程)

In quantum gravity, Hawking radiation presents several fundamental problems. One of the problems is the black hole (BH) information paradox, in which the entanglement entropy (EE), which quantifies quantum entanglement, exceeds its upper bound. In the absence of the paradox, EE follows the Page curve. Recent progress has been made in resolving this paradox using the island formula, a method for computing EE that successfully reproduces the expected Page curve. In this approach, a portion of the black hole interior is treated as part of the radiation region. Meanwhile, an alternative scenario has been proposed where multiple collapsing shells prevent the formation of a well-defined event horizon [1]. In this case, radiation is emitted throughout the collapse process, shifting dynamically the Schwarzschild radius inward, and a surface structure is formed just outside. This leads to a distinction between the conventional event horizon and the surface, introducing an intermediate region between the Schwarzschild radius and the surface. Interestingly, this model also suggests that part of the black hole interior effectively belongs to the radiation region, drawing a possible parallel to the island formula. In this talk, we explore spacetimes with multiple energy injections in asymptotically flat two-dimensional black hole backgrounds and analyze the entanglement entropy in such scenarios. Since considering backreaction in gravitational collapse in two dimensions is difficult, we instead construct a spacetime solution with multiple energy injections and analyze EE within this background. The main focus of this talk is to derive the spacetime and examine its properties. Additionally, we perform EE calculations in parallel with previous studies [2], which consider the case of α single injection, and confirm that the behavior of EE depends on the interval between energy injections.

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

Complexity, expressivity, syntax and semantics

2025年3月14日(金) 14:00 - 14:30

西宮 優作 (理化学研究所 革新知能統合研究センター (AIP) 自然言語理解チーム 研修生)

I will summarise the philosophical motivations behind two research topics; 1. complexity/computability and 2. logic (structural proof theory), and discuss how they may help us understand what makes some problems harder than others, or equivalently, some knowledge more difficult to attain than others (my broad research goals). I. Complexity/computability Computational complexity and computability theory are a subfield of theoretical computer science in which we mathematically study the 'hardness' of problems. We do so by classifying algorithms or a collection of pre-defined rules that some solver can apply without ingenuity by how much time and memory space they require. II. Structural proof theory Even whilst maintaining the basic idea that a well-formed sentence, or a proposition, is either true or false, one can still make a conscious choice about what kind of principles to permit in deriving a new statement from assumptions. Structural proof theory formalises this as a logical-deduction system to study their effect on what the logic can and cannot do. III. What I do, more specifically I take advantage of equivalences between some computational complexity classes and logic, the latter of which, I hope, can serve as an interface to connect, via semantics, complexity with wider mathematics to elucidate something that can tell us what makes some computation inherently costly. IV. 'Computational view' of science I would love to discuss if time permits, how we may apply the idea of complexity to illuminate how information transfers from one thing to another in physical, biological and social systems.

会場: 研究本館 3階 共有スペース

イベント公式言語: 英語

It’s about time! Daily rhythms in malaria infections matter for parasite survival and transmission

2025年3月13日(木) 17:00 - 18:00

Reece Sarah (Professor, University of Edinburgh, UK)

The Reece lab provides a unique perspective on parasites, examining their world within hosts and vectors (insects that transmit parasites). Working at the intersection of parasitology, chronobiology, and evolutionary ecology, our research asks: “what makes a successful parasite” and “what are their evolutionary limits”? Unlike most infection research, that focuses solely on genetics and molecular aspects, our approach considers parasites in their ecological and evolutionary contexts. This has enabled us to uncover the sophisticated strategies that malaria parasites possess, such as optimizing the balance between transmission and replication, strategic investment in each sex of transmission stages, and scheduling activities according to the time of day. By understanding how parasites navigate their challenging lifestyles and seize opportunities, we contribute to interventions that can outsmart parasites and reduce the risk of resistance evolution. Our findings extend beyond the laboratory, showcasing the potential of environmental research to curb the impact of parasitic infections, whether in humans, wildlife, livestock, or agriculture, and helping to protect ecosystems.

会場: via Zoom

イベント公式言語: 英語

RIKEN Quantum hands-on workshop on QURI SDK for creating and executing quantum algorithms on various quantum computers and simulators

2025年3月13日(木) 15:00 - 17:30

This workshop will be a hands-on session on QURI SDK, following the RIKEN Quantum seminar by Andreas Thomasen (QunaSys) on January 27. Even if you did not attend the previous seminar, please join us if you would like to learn how to use QURI SDK.

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

From the Andes to the Lab Bench: Genomic, Evolutionary, and Functional Insights into Amylase Gene Variation and Metabolic Adaptation

2025年3月6日(木) 16:00 - 17:00

Gokcumen Omer (Professor, Department of Biological Sciences, University at Buffalo, USA)

Our laboratory investigates how genomic structural variations (SVs) uniquely drive biological diversity and evolution, surpassing smaller-scale variations like single nucleotide polymorphisms. This talk highlights our work on the amylase locus, a rapidly evolving genomic region shaped by dietary adaptations, frequent duplications, and high mutation rates. I will discuss its convergent evolution across mammals, driven by natural selection linked to starch-rich diets, and describe how long-read sequencing uncovered the mutational mechanisms behind its rapid evolution. We also examine local positive selection in indigenous Andean populations with historically starch-rich diets and how these adaptations impact metabolic health. Finally, I will summarize functional experiments in transgenic mice and diabetic-prone Western Nile rats, relevant models for human metabolism, to investigate the broader metabolic roles of amylase gene duplications. This research provides a roadmap for studying complex SVs in evolution, offering insights into human adaptation and health.

会場: via Zoom / セミナー室 (359号室)

イベント公式言語: 英語

Density-dependent dispersal promotes female-biased sex allocation in viscous populations: From theory to experiment

2025年3月4日(火) 16:00 - 17:00

Chedhawat Chokechaipaisarn (Ph.D. Student, School of Biology, University of St Andrews, UK)

A key prediction in sex allocation theory is that the optimal sex ratio is completely independent to the rate of dispersal. This result challenges the notion of any relationship between dispersal and sex ratio evolution. However, the invariant result is based on the assumption that an individual's dispersal behaviour is not modulated by population density. In this talk, I will explore how density-dependent dispersal impact upon the evolution of sex allocation in a viscous-population setting. Additionally, I will discuss the process of testing this prediction through experimental evolution in spider mites.

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 Cosmology Forum 3 - (P)reheating the primordial Universe

2025年3月4日(火) - 5日(水)

榎本 成志 (横浜国立大学 理工学部 博士研究員)
John T. Giblin (Professor, Department of Physics, Kenyon College, USA)
向田 享平 (高エネルギー加速器研究機構 (KEK) 理論センター 助教)

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focusing on an emerging topics in cosmology. The target audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants. The third workshop is devoted to the 'reheating' phase of the early Universe. Reheating bridges the gap between the (almost) empty universe at the end of cosmic inflation and the thermal state of particles, required for Big-Bang nucleosynthesis, and the events of the hot Big-Bang model as a whole, to unfold. It is expected to proceed in different stages starting with a violent parametric resonant creation of particles, dubbed preheating, followed by a redistribution of energy leading to a thermal state. This phase potentially hosts rich phenomenology such as the formation of topoligical defects e.g. solitons, generation of gravitiational wave, and so on. Yet, the very non-linear nature of reheating makes it notoriously hard to describe analytically, and even numerical simulations struggle to follow the whole sequence of events in a given model. Reheating studies have thus yet to reach the degree of compherensiveness and universality that the understanding of cosmic inflation has achieved. This forum will consist of two events. The first, on March 4th, will be in conference format comprising scientific talks on research trends in (P)Reheating. The second, on March 5th, will be a tutorial on numerical aspects of reheating (both theory and hands-on with code) hosted by Tom Giblin of Kenyon College. The workshop will be in English. The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS. Important dates: Feb. 25th - Registration deadline March 4th - Workshop Day (Room #435-437, Main Research Building 4F) March 5th - Tutorial Day (Room #445-447, Main Research Building 4F) Invited Speakers: John T. Giblin - Kenyon College Kyohei Mukaida - KEK Seishi Enomoto - Yokohama National University Organisers: Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

会場: 研究本館 4階 435-437号室 / 研究本館 4階 445-447号室

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