iTHEMS Colloquium
22 events

From the Black Hole Conundrum to the Structure of Quantum Gravity
July 26 (Tue) at 15:30  17:00, 2022
Prof. Yasunori Nomura (Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)
Having a complete quantum theory of gravity has long been a major goal of theoretical physics. This is because a naive merger of quantum mechanics and general relativity — though it works in certain limited regimes — suffers from major theoretical problems. A particularly acute one arises when one considers the quantum mechanics of black holes: two fundamental principles of modern physics — the conservation of probability in quantum mechanics and the equivalence principle of general relativity — seem to be incompatible with each other. I will explain how recent theoretical progress begins to address this problem and portray the emerging picture of how spacetime and gravity behave at the level of full quantum gravity.
Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus / via Zoom
Event Official Language: English

How is turbulence born: Statistical mechanics and ecological collapse in transitional fluids
April 22 (Fri) at 15:00  16:30, 2022
Dr. HongYan Shih (Assistant Research Fellow, Institute of Physics, Academia Sinica, Taiwan)
The onset of turbulence is ubiquitous in daily life and is important in various industrial applications, yet how fluids become turbulent has remained unsolved for more than a century. Recent experiments in pipe flow finally quantified this transition, showing that nontrivial statistics and spatiotemporal complexity develop as the flow velocity is increased. Combining numerical simulations of the hydrodynamics equations and an effective theory from statistical mechanics, we discovered the surprising fact that fluid behavior at the transition is governed by the emergent predatorprey dynamics, leading to the mathematical prediction that the laminarturbulent transition is analogous to an ecosystem on the edge of extinction. This prediction demonstrates that the laminarturbulent transition is a nonequilibrium phase transition in the directed percolation universality class, and provides a unified picture of transition to turbulence in various systems. I will also show our recent progresses on transitional turbulence, including how an extended ecological model with energy balance successfully recapitulates the spatiotemporal patterns beyond the critical point, and the determination of the critical behavior and an emergent novel phase under interactions in the experimental collaboration.
Venue: via Zoom
Event Official Language: English

HighEnergy Neutrino Astrophysics in the Multimessenger Era
October 28 (Thu) at 15:00  16:30, 2021
Prof. Kohta Murase (Associate Professor, Pennsylvania State University, USA)
The discovery of highenergy cosmic neutrinos opened a new window of astroparticle physics. Their origin is a new mystery in the field, which is tightly connected to the longstanding puzzle about the origin of cosmic rays. I will give an overview of the latest results on highenergy neutrino and cosmicray observations, and demonstrate the power of "multimessenger" approaches. In particular, I will show that the observed fluxes of neutrinos, gamma rays, and extragalactic cosmic rays can be understood in a unified manner. I will also highlight the recent developments about astrophysical neutrino emission from supermassive black holes and violent transient phenomena. Possibilities of utilizing highenergy neutrinos as a probe of heavy dark matter may be discussed.
Venue: via Zoom
Event Official Language: English

Finding Gravitational Waves from the Early Universe
September 27 (Mon) at 16:00  17:30, 2021
Prof. Eiichiro Komatsu (Director, Max Planck Institute for Astrophysics, Germany)
The Cosmic Microwave Background (CMB) gives a photographic image of the Universe when it was still an “infant”. We have been using it to test our ideas about the origin of the Universe. The CMB research told us a remarkable story: the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations in the period of the early Universe called cosmic inflation. While we have accumulated strong evidence for this picture, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called LiteBIRD, whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe physics of gravitational waves from inflation, and the LiteBIRD proposal.
Venue: via Zoom
Event Official Language: English

Quantitative Population Dynamics in Interdisciplinary Biology
July 8 (Thu) at 10:30  12:00, 2021
Prof. Shingo Iwami (Professor, Division of Biological Science, Graduate School of Science, Nagoya University)
Through the course of life, from the moment of birth till death, an organism will achieve various states of equilibrium or ‘homeostasis’ which will inevitably encounter perturbations. The processes of cell growth, differentiation, infection, mutation, evolution and adaptation work together as a coordinated ‘system’, described by mathematical models for population dynamics, to maintain a healthy state. Any disruptions to this system leads to disease including infection, allergy, cancer, and aging. We are conducting interdisciplinary research to elucidate “Quantitative Population Dynamics” through the course of life with original mathematical theory and computational simulation, which are both our CORE approach. Our mathematical modelbased approach has quantitatively improved a current goldstandard approach essentially relying on the statistical analysis of “snapshot data” during dynamic interaction processes in life sciences research. In this talk, I will explain how our interdisciplinary approach extends our understanding for complicated clinical data and apply real world problem with an example of the Novel Coronavirus Disease, COVID19.
Venue: via Zoom
Event Official Language: English

Mirror symmetry and KAM theory
April 16 (Fri) at 13:30  15:00, 2021
Prof. Kenji Fukaya (Permanent Member, Simons Center for Geometry and Physics, Stony Brook University, New York, USA)
13:30pm15:00pm (JST) Mirror symmetry is a phenomenon discovered in String theory and is much discussed recently in mathematics especially in the field of complex (algebraic) geometry and symplectic geometry. StromingerYauZaslow found that this phenomenon is closed related to a Lagrangian torus fibration. In an integrable system in Hamiltonian dynamics, the phase space is foliated by Lagrangian tori. I would like to explain a program that the Lagrangian torus fibration found by StromingerYauZaslow could be regarded as one appearing certain integrable system and KAM theory (which describes a amiltonian dynamics that is a perturbation of an integrable system) could appear in the situation of Mirror symmetry.
Venue: via Zoom
Event Official Language: English

Geometry (形); Inconspicuous regulator that determines the fate of cells
December 14 (Mon) at 10:00  11:30, 2020
Prof. Sungrim SeirinLee (Professor, Hiroshima University)
December 14 at 10:0011:30, 2020 (JST) December 13 at 20:0021:30, 2020 (EST) In the history of mathematical study in pattern formation, the effect of domain has been considered as an important factor that can regulate spatial patterning. However, it is still unknown in biology how the geometry of the domain such as nuclear or cellular shapes can directly regulate the cell fate. In this talk, I will introduce two studies of spatial reorganization in chromatin and cellular dynamics and show that the domain is likely to play a critical role in determining the cell function.
Venue: via Zoom
Event Official Language: English

The Unreasonable Effectiveness of Quantum Theory in Mathematics
November 26 (Thu) at 10:00  11:30, 2020
Prof. Robbert Dijkgraaf (Director, Institute for Advanced Study in Princeton, USA)
November 26 at 10:0011:30, 2020 (JST) November 25 at 20:0021:30, 2020 (EST) The physical concepts of quantum theory, in particular of quantum gravity and string theory, have proven to be extremely powerful in addressing deep problems in pure mathematics, from knot invariants to algebraic geometry. Is there such a thing as “quantum mathematics”? Should we add Feynman diagrams, strings, branes and black holes to the language of mathematics?
Venue: via Zoom
Event Official Language: English

iTHEMS Intensive Course [4] : "Adaptive strategies of organisms, their mathematical bases"  Cancer as a minievolutionary process
June 25 (Thu) at 15:00  16:30, 2020
Prof. Yoh Iwasa (Senior Advisor, iTHEMS / Professor, Kwansei Gakuin University / Professor Emeritus, Kyushu University)
Living systems exhibit features distinct from nonliving physical systems: their structure and behaviors appear to be chosen adaptive. They are the outcomes of evolution. Mathematical formalisms developed in engineering and social sciences (e.g. control theory, game theory, evolutionary game theory) are sometimes very useful in biology.
Venue: via Zoom
Event Official Language: English

Emergence of life in an inflationary universe
May 11 (Mon) at 15:30  17:00, 2020
Dr. Tomonori Totani (Professor, Department of Astronomy, Graduate School of Science, The University of Tokyo)
The origin of life may be the greatest mystery in natural science. Especially, we know almost nothing about how the first biological molecule (possibly an RNA) appeared from abiotic chemical processes. A widespread notion is that the abiogenesis probability is extremely low when we consider only random chemical reactions to polymerize a large biological molecule. However, we do not know any more efficient polymerization process expected to work in a realistic prebiotic environment. Here, I consider this problem from a viewpoint of cosmology. Cosmologists agree that the universe created by an inflation should extend far beyond the observable universe (13.8 billion light year radius). Then the inflationary universe may be sufficiently large to produce many abiogenesis events, even if we consider only the basic random polymerization. I will give a quantitative answer to this question, and discuss various implications about the originoflife studies.
Venue: via Zoom
Event Official Language: English

Interaction Models in Quantum Optics, Representation Theory and Number Theory
April 10 (Fri) at 15:30  17:00, 2020
Dr. Masato Wakayama (Senior Advisor, iTHEMS / Vice President, Tokyo University of Science)
Recently, interaction models originated in quantum optics, with the quantum Rabi model (QRM) as a distinguished representative, are appearing ubiquitously in various quantum systems including cavity and circuit quantum electrodynamics, quantum dots and artificial atoms, with potential applications to quantum information technologies such as quantum computing. Together with the integrability of QRM, demonstrated by Daniel Braak in 2011, this has led to wide discussion and development of various aspect of the QRM and its generalizations from the point of view of theoretical physics and mathematics. In this talk, firstly, we characterize the structure of the spectra of QRM and its asymmetric version via sℓ2representations. Secondly, we introduce the noncommutative harmonic oscillator, which may be considered to be a “cover” of the QRM in the Heun ODE picture, and describe certain number theoretical aspects arising from its spectral zeta function. Further, we discuss the heat kernel and partition function of the QRM toward the number theoretical investigation of the model. In addition, a number of related open problems will be presented.
Venue: via Zoom
Event Official Language: English

Exploring the learning principle in the brain
January 16 (Thu) at 15:30  17:00, 2020
Dr. Taro Toyoizumi (Team Leader, RIKEN Center for Brain Science (CBS))
Animals adapt to the environment for survival. Synaptic plasticity is considered a major mechanism underlying this process. However, the bestknown form of synaptic plasticity, i.e., Hebbian plasticity that depends on pre and postsynaptic activity, can surge coincident activity in model neurons beyond a physiological range. Our lab has explored how neural circuits learn about the environment by synaptic plasticity. The instability of Hebbian plasticity could be mitigated by a global factor that modulates its outcome. For example, TNFalpha that mediates homeostatic synaptic scaling is released by glia, reflecting the activity level of surrounding neurons. I show that a specific interaction of Hebbian plasticity with this global factor accounts for the time course of adaptation to the altered environment (Toyoizumi et al. 2015). At a more theoretical level, I ask what is the optimal synaptic plasticity rule for achieving an efficient representation of the environment. A solution is the errorgated Hebbian rule, whose update is proportional to the product of Hebbian change and a specific global factor. I show that this rule, suitable also in neuromorphic devices, robustly extracts hidden independent sources in the environment (Isomura and Toyoizumi 2016, 2018, 2019). Finally, I introduce that synapses change by intrinsic spine dynamics, even in the absence of synaptic plasticity. I show that physiological spinevolume distribution and stable cell assemblies are both achieved when intrinsic spine dynamics are augmented in a model (Humble et al.2019).
Venue: Large Meeting Room, 2F Welfare and Conference Building (Cafeteria)
Broadcast:R311, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

Topological phases of matter and operator algebras
October 4 (Fri) at 15:30  17:00, 2019
Prof. Yasuyuki Kawahigashi (Senior Visiting Scientist, iTHEMS / Professor, Graduate School of Mathematical Sciences, The University of Tokyo)
Topological phases of matter are hot topics in recent physics and related to a wide range of mathematical fields. I will talk about their aspects related to operator algebras. Our emphasis will be on theory of tensor categories which describe interactions of anyons. This theory plays an important role in topological quantum computations. In theory of operator algebras, Jones initiated theory of subfactors and discovered the Jones polynomial, a new topological invariant for knots as an application. We apply this theory to mathematical studies of anyons.
Venue: Okochi Hall
Broadcast:R511, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

Spacetime Geometry of Black Holes, Wormholes, and Time Machines
July 2 (Tue) at 15:30  17:00, 2019
Prof. PeiMing Ho (Department of Physics, National Taiwan University, Taiwan)
Since the advent of General Relativity, people have found many solutions with interesting spacetime geometries. Most notably, the black holes have attracted a lot of attention for their roles in generating gravitational waves, and for inducing the information loss paradox. In this talk, we consider black holes amongst other geometric structures and investigate the subtlety involved in the quantum effect such as Hawking radiation. In this context, we mention wormholes and time machines, and explain how they are conceptually related to the geometry under the horizon of a black hole. There will also be comments on my recent research result about how quantum effect must be large for observers sitting on top of the black hole horizon.
Venue: Large Meeting Room, 2F Welfare and Conference Building (Cafeteria)
Broadcast:R511, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

Quantum computing: current status and prospects
April 25 (Thu) at 15:00  16:30, 2019
Dr. Keisuke Fujii (Kyoto University)
Supported by extensive experimental efforts for realization of quantum computing devices, quantum computers of a hundred qubits are now within reach in the near future. This level of a quantum computer is not enough for fully fledged faulttolerant quantum computing, but is still expected to have computational advantage against classical computers. Such a noisy intermediate scale quantum computing (NISQ) device is thought to be a testbed for proofofprinciple experiments of quantum algorithms and verification of quantum physics in the limit of extremely high complexity. In this talk, I will provide a general introduction to quantum computing starting from how and for what quantum computers work. Then I will provide an overview of the current status and prospects of the field of quantum computing. As the final part, I will also talk about our own activities on quantumclassical hybrid algorithm, which is a kind of quantum algorithms specifically designed for the NISQ devices.
Venue: Suzuki Umetaro Hall
Broadcast:R511, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

ZetaValue2019iTHEMS Special Mathematics Colloquium
March 21 (Thu) at 14:00  17:30, 2019
Prof. Kohji Matsumoto (Professor, Nagoya University)
Prof. Jörn Steuding (University of Würzburg, Germany)Prof. Kohji Matsumoto (Nagoya University) "An overview of the theory of multiple zetafunctions" Multiple zetafunctions are generalizations of the Riemann zetafunction, and its theory has been rapidly developed in these decades. It is connected with various fields of mathematics and mathematical physics. In this talk I will give an overview of some part of recent developments, mainly from the analytic viewpoint. Prof. Jörn Steuding (University of Würzburg, Germany) "On the Infinite in Number Theory" Beginning with two simple examples from elementary number theory (one of diophantine origin and one of arithmetical nature), we discuss the role of “infinity” in number theory. We touch upon topics like how to find good rational approximations to irrational quantities and the distribution of prime numbers. We conclude with a motivation of the big open question in this field, namely, the Riemann hypothesis (one of the six unsolved millennium problems) and the Langlands program.
Venue: Okochi Hall
Event Official Language: English

Tropical Rain Forest
February 21 (Thu) at 15:30  17:00, 2019
Prof. Akiko Satake (Professor, Mathematical Biology Laboratory, Department of Biology, Faculty of Science, Kyushu University)
In a unique phenomenon restricted to the tropical rain forests in Southeast Asia, hundreds of plant species from dozens of families reproduce synchronously at irregular, multiyear intervals. Although several hypotheses have been proposed, the proximate environmental cues that synchronize these general flowering events are uncertain. Fortunately, accumulation of longterm data and advanced statistical and modeling techniques are starting to shed new light on phenology of tropical plants. In this talk, series of studies that integrate longterm field monitoring, gene expression analyses, and modeling will be presented.
Venue: Okochi Hall
Broadcast:#311, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

Economic Networks: a Physicist's View
October 3 (Wed) at 15:00  16:30, 2018
Prof. Hideaki Aoyama (Senior Visiting Scientist, iTHEMS / Professor, Graduate School of Science, Kyoto University)
Economic phenomena occur on networks formed by agents, such as firms and financial institutions. In order to understand the dynamic nature of economy, we need to understand structures of those networks and interactions between economic agents on it. In this talk, I will review several important research results on this theme, most of which uses Japanese rich, actual (not simulated) network data, including trade (production) network of about one million firms. Community structures, simulation of effect of natural disasters, new methodology required for such inquiry are some of the topics to be covered.
Venue: Large Meeting Room, 2F Welfare and Conference Building (Cafeteria)
Broadcast:R511, Computational Science Research Building / SUURICOOL (Kyoto) / SUURICOOL (Sendai)
Event Official Language: English

Bell's Theorem, Entanglement, Quantum Teleportation and All That
July 19 (Thu) at 16:00  17:30, 2018
Prof. Anthony James Leggett (Professor, University of Illinois at UrbanaChampaign, USA)
iTHEMSCEMS Joint Colloquium. Professor Leggett is widely recognized as a world leader in the theory of lowtemperature physics, and his pioneering work on superfluidity was recognized by the 2003 Nobel Prize in Physics. Abstract: One of the most surprising aspects of quantum mechanics is that under certain circumstances it does not allow individual physical systems, even when isolated, to possess properties in their own right. This feature, first clearly appreciated by John Bell in 1964, has over the last halfcentury been tested experimentally and found (in most people's opinion) to be spectacularly confirmed. More recently it has been realized that it permits various operations which are classically impossible, such as "teleportation" and secureinprinciple cryptography. This talk is a very basic introduction to the subject, which requires only elementary quantum mechanics.
Venue: Okochi Hall
Broadcast:#311, Computational Science Research Building / SUURICOOL (Kyoto) / 2F Seminar Room, AIMR Main Building
Event Official Language: English

Systems Biology of Cellular Rhythms
July 2 (Mon) at 15:00  16:30, 2018
Prof. Albert Goldbeter (Professor, Unit of Theoretical Chronobiology, Faculty of Sciences, Université Libre de Bruxelles, Belgium)
Rhythmic phenomena occur at all levels of biological organization, with periods ranging from milliseconds to years. Among biological rhythms, circadian clocks, of a period close to 24h, play a key role as they allow the adaptation of living organisms to the alternation of day and night. Biological rhythms represent a phenomenon of temporal selforganization in the form of sustained oscillations of the limit cycle type. Mathematical models show how the emergent property of oscillatory behavior arises from molecular interactions in cellular regulatory networks, which explains why cellular rhythms represent a major research topic in systems biology. After providing an introduction to biological rhythms and their modeling, I will focus on mathematical models for two major examples of rhythmic behavior at the cellular level : the circadian clock and the cell cycle. The coupling of these rhythms allows for their synchronization and for the occurrence of more complex patterns of oscillatory behavior. I will discuss the reasons why models for cellular rhythms tend to become more complex, upon incorporating new experimental observations. The case of cellular rhythms allows us to compare the merits of simple versus complex models for the dynamics of biological systems.
Venue: Suzuki Umetaro Hall
Broadcast:#3052, Computational Science Research Building / SUURICOOL (Kyoto) / 2F Seminar Room, AIMR Main Building
Event Official Language: English
22 events
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