141 events in 2021

Tetsuo Hatsuda x Kunihiko Nakata x Yoshihiro Kozuka x Kenshiro Sadaka x Aiko Teranishi  Will Useless Knowledge Change the Future?  What is the Black Hole Recorder?
August 2 (Mon) at 20:00  22:00, 2021
Tetsuo Hatsuda (Program Director, iTHEMS)
Kunihiko Nakata (NAKATA KUNIHIKO DESIGN)
Yoshihiro Kozuka (ADK Holdings Inc.)
Kenshiro Sadaka (ADK Holdings Inc.)
Aiko Teranishi (President and CEO, indigo.inc)This event will feature a thorough explanation of the "Black Hole Recorder," a device inspired by the latest black hole theory. Free of charge. Registration required.
Venue: via Zoom
Event Official Language: Japanese

Seminar
Application of bioenergetics to microbial modeling
July 29 (Thu) at 10:00  11:00, 2021
Mayumi Seto (Assistant Professor, Department of Chmistry, Biology, and Environmental Science, Faculty of Science, Nara Women's University)
Bioenergetics, the study of thermodynamics as applied to biological systems, aims to understand how energy flows through a living system. Since thermodynamics provides a framework for predicting the progress of a spontaneous reaction and for harnessing the energy released, bioenergetics can help us to understand the ecological processes of chemotrophic microorganisms that harvest metabolic energy from various chemical reactions. In this talk, I will introduce a theoretical model as an attempt to describe the growth of chemotrophic microorganisms in terms of the interrelationships between microbial activities and the change in Gibbs energy of a system. Based on our findings and previous literature in the field, I will discuss ecological insights into microbial ecosystems thriving in lowenergy environment.
Venue: via Zoom
Event Official Language: English

Seminar
Overview of Tensor Networks in Machine Learning
July 28 (Wed) at 13:30  14:50, 2021
Qibin Zhao (Team Leader, Tensor Learning Team, RIKEN Center for Advanced Intelligence Project (AIP))
Tensor Networks (TNs) are factorizations of high dimensional tensors into networks of many lowdimensional tensors, which have been studied in quantum physics, highperformance computing, and applied mathematics. In recent years, TNs have been increasingly investigated and applied to machine learning and signal processing, due to its significant advances in handling largescale and highdimensional problems, model compression in deep neural networks, and efficient computations for learning algorithms. This talk aims to present a broad overview of recent progress of TNs technology applied to machine learning from perspectives of basic principle and algorithms, novel approaches in unsupervised learning, tensor completion, multitask, multimodel learning and various applications in DNN, CNN, RNN and etc. We also discuss the future research directions and new trend in this area.
Venue: via Zoom
Event Official Language: English

Workshop
iTHEMS Science Outreach Workshop 2021
July 11 (Sun)  12 (Mon), 2021
RIKEN iTHEMS, an interdisciplinary Theoretical and Mathematical Sciences Program (RIKEN iTHEMS), was established in November 2016. RIKEN iTHEMS aims to use interdisciplinary methods with a focus on mathematics to elucidate the universe, matter and life, and to solve fundamental problems in society. Building on the achievements of the past exchanges through the Journalist in Residence Program, we will hold an outreach workshop to explore the relevance of the research of the RIKEN iTHEMS to society and to discuss how to build interactive relationships between journalists and researchers in the future. Like last year, this year's workshop will be held as a ZOOM workshop as the seminar house is closed. Contact: Takashi Tsuboi (iTHEMS Deputy Director)
Venue: via Zoom
Event Official Language: Japanese

Seminar
Fallback Accretion in Binary Neutron Star Mergers
July 9 (Fri) at 16:00  17:30, 2021
Wataru Ishizaki (Postdoctoral Fellows, Yukawa Institute for Theoretical Physics, Kyoto University)
The gravitational wave event GW170817 with a kilonova shows that a merger of two neutron stars ejects matter with radioactivity including rprocess nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering longlasting activities of a short gammaray burst (sGRB), such as extended and plateau emissions. We investigate the fallback accretion with the rprocess heating by performing onedimensional hydrodynamic simulations and developing a semianalytical model. We show that the usual fallback rate dM/dt \propto t^{5/3} is halted by the heating. The characteristic halting timescale is $\sim 10^4$$10^8$ sec for the GW170817like rprocess heating, which is long enough to continue the longlasting emission of sGRBs. Furthermore, we propose a new interpretation of the recently reported rebrightening in the annualscale Xray light curve of GW170817. We model the fallback of the merger ejecta and construct a simple light curve model from the accreting ejecta. We find that the Xray flux excess can be well explained by the fallback of the postmerger ejecta such as the disk wind from the accretion disk of the merger remnant rather than by the fallback of the dynamical ejecta. The duration of the constant luminosity phase conveys the initial fallback timescale t_0 in the past. Future observations in the next decades will probe the timescale of t_0 \sim 1010^4 sec, around the time of extended emission in short gammaray bursts.
Venue: via Zoom
Event Official Language: English

Quantitative Population Dynamics in Interdisciplinary Biology
July 8 (Thu) at 10:30  12:00, 2021
Shingo Iwami (Professor, 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

The 16th MACS Colloquium
July 5 (Mon) at 15:00  18:00, 2021
Yoshitaka Tanimura (Professor, Department of Chemistry, Graduate School of Science, Kyoto University)
Hidetoshi Nishimori (Senior Visiting Scientist, iTHEMS / Specially Appointed Professor, Tokyo Institute of Technology)15:00 Talk by Prof. Yoshitaka Tanimura 16:15 Talk by Prof. Hidetoshi Nishimori 17:15 Discussion
Venue: via Zoom
Event Official Language: Japanese

Seminar
NonUnitary TQFTs from 3d N=4 Rank0 SCFTs
July 5 (Mon) at 13:00  14:30, 2021
Myungbo Shim (Kyung Hee University, Republic of Korea)
We propose a novel procedure of assigning a pair of nonunitary topological quantum field theories (TQFTs), TFT_\pm[T_0], to a (2+1)D interacting N=4 superconformal field theory (SCFT) T_0 of rank 0, i.e. having no Coulomb and Higgs branches. The topological theories arise from particular degenerate limits of the SCFT. Modular data of the nonunitary TQFTs are extracted from the supersymmetric partition functions in the degenerate limits. As a nontrivial dictionary, we propose that F = max{ log S^{(+)}_{0\alpha} } = max{ log S^{()}_{0\alpha} }, where F is the round threesphere free energy of T_0 and S^{(\pm)}_{0\alpha} is the first column in the modular Smatrix of TFT_\pm. From the dictionary, we derive the lower bound on F, F > log(\sqrt{(5\sqrt{5})/10}) \simeq 0.642965, which holds for any rank 0 SCFT. The bound is saturated by the minimal N=4 SCFT proposed by GangYamazaki, whose associated topological theories are both the LeeYang TQFT. We explicitly work out the (rank 0 SCFT)/(nonunitary TQFTs) correspondence for infinitely many examples. Before going to the technical part, we provide some background materials including some peculiar features in 3d gauge theories, some supersymmetries, anyons, and some modular data of MTC in this talk.
Venue: via Zoom
Event Official Language: English

An introduction to modular functions, conformal field theories, and moonshine phenomena
July 2 (Fri) at 16:00  18:10, 2021
Mizuki Oikawa (Junior Research Associate, iTHEMS / Student Trainee, iTHEMS / Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)
Moonshine phenomena are certain mysterious connections between modular functions and finite groups. The first example is the celebrated monstrous moonshine, which connects the Jinvariant and the Monster group. Surprisingly, this relationship can be well understood in terms of chiral conformal field theory. In this talk, I would like to explain what is chiral conformal field theory and how it gives moonshine phenomena. In the first part of the talk, the notion of modular function will be introduced and the precise statement of the monstrous moonshine will be given. Then the monstrous moonshine will be explained in terms of vertex operator algebra, a mathematical model of chiral conformal field theory. In the second part of the talk, we focus on the question: what is chiral conformal field theory mathematically? In addition to vertex operator algebras, other mathematical models of chiral conformal field theory, namely conformal nets and Segal conformal field theories, will be introduced. Recent progress on the relationship among these three models, including the CarpiKawahigashiLongoWeiner correspondence and the geometric realization of conformal nets will also be reviewed.
Venue: via Zoom
Event Official Language: English

How nucleus size affects chromatin motion?  Experimental measurements and a polymer physics theory
July 1 (Thu) at 10:00  11:00, 2021
Takahiro Sakaue (Associate Professor, College of Science and Engineering, Department of Physics and Mathematics, Aoyama Gakuin University)
Chromatin moves dynamically inside the cell nucleus, and its motion is often correlated with gene functions such as DNA recombination and transcription. A recent study has shown that during early embryogenesis of the nematode, Caenorhabditis elegans, the chromatin motion markedly decreases with the cell stage. However, the underlying mechanism for this transition has yet to be elucidated. Here we systematically investigate the impact of nuclear size to demonstrate that it is indeed a decisive factor in chromatin mobility. We show that a simple theoretical description, which takes into account the length and time scales of chromatin polymer solution, can quantitatively describe the relationship between the nucleus size and the chromatin motion in vivo. Our results emphasize a regulatory role of nuclear size in restricting chromatin motion, and a generic polymer physics model plays a guiding role in capturing this essential feature. *Please refer to the email to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English

Seminar
Toward QCDbased description of dense baryonic matter
June 29 (Tue) at 13:00  14:30, 2021
Yuki Fujimoto (Postdoctoral Scholars, Department of Physics, University of Washington, USA)
The equation of state (EoS) of dense baryonic/quark matter is the crucial ingredient for understanding neutron stars. I briefly review the current state of the highdensity matter EoS based on the QCD perspectives. In this talk, I particularly focus on the perturbative QCD (pQCD) EoS, which was previously thought to be useless at realistic density because it is plagued by the large uncertainty. I introduce our recent analysis of the EoS calculated within the pQCD framework with the resummation [Fujimoto & Fukushima, 2011.10891]. I discuss our scheme for the Hard Dense Loop resummation, which turns out to reduce the uncertainty compared with the conventional pQCD estimate without resummation. Our result apparently extends the applicability of the QCDbased EoS down to densities realized inside neutron stars and infers a smooth matching with the baryonic EoS.
Venue: via Zoom
Event Official Language: English

RIKEN Day: Let's Talk with Researchers! "Can Artificial Intelligence Draw Pictures?"
June 25 (Fri) at 18:00  18:30, 2021
Akinori Tanaka (Senior Research Scientist, iTHEMS)
In the June RIKEN Day, we will have a talk with Akinori Tanaka, a researcher who is researching on the theme of "Can Artificial Intelligence Draw Pictures?" See related links for details.
Venue: via Zoom
Event Official Language: Japanese

Theory of CoreCollapse Supernovae
June 25 (Fri) at 16:00  17:00, 2021
Akira Harada (Special Postdoctoral Researcher, iTHEMS)
Venue: via Zoom
Event Official Language: English

Seminar
Precise WIMP Dark Matter Abundance and Standard Model Thermodynamics
June 24 (Thu) at 16:30  17:30, 2021
Satoshi Shirai (Project Assistant Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)
We are now living in the era of precision cosmology. The relic abundance of dark matter (DM) is now observationally welldetermined, and its error is smaller than O(1)%. This means that the same or much higher precision is required when we make theoretical predictions. Weakly Interacting Massive Particle (WIMP) has long been the leading candidate for DM because of its beautiful mechanism to predict the observed relic abundance. WIMP is in the same thermal bath as the Standard Model particles in the beginning. At a certain point when the temperature of the Universe is smaller than the DM mass, it decouples to fix its number density. The yield of the DM is determined by its annihilation crosssection to the Standard Model sector. It seems that there is no ambiguity in the calculation of this process at first: the crosssection is purely theoretical and all the remainings are described in the Standard Model physics. However, the source of the uncertainty does remain in the Standard Model sector. The dilution of the number density of DM particle depends on the expansion rate of the Universe, which is determined by the Standard Model particles. The effective degree of freedom (d.o.f) of the relativistic species controls this factor. We have to deal with the nonequilibrium dynamics to precisely describe the timeevolution of the d.o.f, in which we need numerical approaches. In this talk, he introduced his work to update these calculations. By implementing the latest findings in the nonequilibrium dynamics in i) the neutrino decoupling, ii) the QCD phase transition, iii) the electroweak phase transition, and iv) the perturbative calculations, they found that the final d.o.f is smaller than the previous estimate in more than 1%. This is larger than the level of precision in observations. It is also important that the uncertainty is quantified by them. Another good news is that he makes the calculated d.o.f with its error publically available. With these updates, we now correctly know the points to probe DM!
Venue: via Zoom
Event Official Language: English

Seminar
Period variability can provide valuable information in oscillatory systems
June 24 (Thu) at 10:00  11:00, 2021
Fumito Mori (Assistant Professor, Department of Human Science, Faculty of Design, Kyushu University)
Biological clocks generate temporally precise oscillations although they are subjected to various types of noise. In other words, oscillations with only a small variability in the period are observed under action of noise. In this talk, I focus on period variability in coupled phase oscillators and complex oscillatory dynamical systems, and present the following topics:(i) A phase oscillator subjected to noise can become to generate more precise oscillations not only when it is synchronized with periodic signal but also when it is mutually synchronized with another phase oscillator with stronger noise. (ii) In complex oscillatory dynamical systems, period variability is sensitive to the choice of an output variable and output checkpoint; it can be reduced by an appropriate selection of them. (iii) Noise intensity and coupling strength in synchronized phase oscillators can be inferred from data about period variability. This talk is based on joint researches with Dr. Hiroshi Kori (Tokyo Univ) and Dr. Alexander Mikhailov (Kanazawa Univ). *Please refer to the email to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English

Seminar
Introduction to the replica method
June 23 (Wed) at 13:30  15:40, 2021
Yoshiyuki Kabashima (Professor, Graduate School of Science, The University of Tokyo)
The replica method is a mathematical technique for evaluating the "quenched" average of logarithm (or a real number power) of the partition function with respect to predetermined random variables that condition the objective system. The technique has a long history, dating back at least to a book by Hardy et al in 1930s, but has become well known only since its application to the physics of spin glasses in 1970s. More recently, its application range is spreading rapidly to various fields in information science, including information theory, communication theory, signal processing, computational complexity theory, machine learning, etc. In this talk, we introduce the basic idea of the replica method and its mathematical fault illustrating a few examples. *Detailed information about the seminar refer to the email.
Venue: via Zoom
Event Official Language: English

Black Hole Information Paradox and Wormholes
June 21 (Mon) at 13:00  14:30, 2021
Kanato Goto (Special Postdoctoral Researcher, iTHEMS)
In this talk, I will explain about the recent progress in the black hole information paradox that I am involved with. The information paradox arises when a black hole evaporates by emitting Hawking radiation due to the quantum effects. Time dependence of the entropy of Hawking radiation is diagnosis of information loss caused by the black hole evaporation. If information is not lost, the entropy of Hawking radiation should obey the socalled Page curve. In recent research developments, it was found that “the quantum extremal islands” reproduce the unitary Page curve in an evaporating black hole. I will argue about how the quantum extremal islands are derived from the computation of the entropy of Hawking radiation using the gravitational pathintegral.
Venue: via Zoom
Event Official Language: English

Stable eigenvalues of compact antide Sitter 3manifolds
June 18 (Fri) at 16:00  18:10, 2021
Kazuki Kannaka (Special Postdoctoral Researcher, iTHEMS)
Geometric objects that have been investigated in detail so far, such as closed Riemann surfaces, are sometimes locally homogeneous. Loosely speaking, their infinitesimal behavior is the same at each point. In this talk, I would like to explain the idea of investigating such objects using the Lie group theory.In the first part of the talk, I will recall the notions of Lie group actions and their quotient spaces with examples, and then explain the definitions of locally homogeneous spaces and their deformations (Teichmüller spaces). In the second part of the talk, I will consider antide Sitter manifolds as a special case, i.e., Lorentzian manifolds of negative constant curvature. As in the Riemannian case, a differential operator called the Laplacian (or the KleinGordon operator) is defined on Lorentzian manifolds. Unlike the Riemannian case, it is no longer an elliptic differential operator but a hyperbolic differential operator. In its spectral analysis, new phenomena different from those in the Riemannian case have been discovered in recent years, following pioneering works by Toshiyuki Kobayashi and Fanny Kassel. I would like to explain stable eigenvalues of the hyperbolic Laplacian of antide Sitter 3manifolds with recent progress.
Venue: via Zoom
Event Official Language: English

The origin and dispersal of buckwheat
June 10 (Thu) at 10:00  11:00, 2021
Jeffrey Fawcett (Senior Research Scientist, iTHEMS)
Buckwheat, which soba noodles is made from, originated from a wild species that is distributed in southwest China, around Yunnan, Sichuan, and Tibet. We are trying to understand when, where, and how it originated and then spread across the world and came to Japan. To do so, we are using genomic data of wild samples from China and cultivated samples from various parts of the world. I will give a brief introduction about buckwheat, explain what we already know about its origin and dispersal, and show a bit of our results. I will also explain the significance of studying "domestication", that is, the process that plants/animals that humans currently use originated from their ancestral wild species. *Please refer to the email to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English

iTHEMSphys Intro Meeting on June 7, 2021
June 7 (Mon) at 13:00  14:30, 2021
Tomoya Naito (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)
Takeru Yokota (Postdoctoral Researcher, The Institute for Solid State Physics (ISSP), The University of Tokyo)
Naomi Tsuji (Postdoctoral Researcher, iTHEMS)13:0013:20 [JST] Tomoya Naito 13:2013:40 [JST] Takeru Yokota 13:4014:00 [JST] Naomi Tsuji 14:00 Free discussion
Venue: via Zoom
Event Official Language: English
141 events in 2021
Events
Categories
series
 iTHEMS Colloquium
 MACS Colloquium
 iTHEMS Seminar
 iTHEMS Math Seminar
 DMWG Seminar
 iTHEMS Biology Seminar
 iTHEMS Theoretical Physics Seminar
 Information Theory SG Seminar
 Quantum Matter Seminar
 ABBLiTHEMS Joint Astro Seminar
 MathPhys Seminar
 Quantum Gravity Gatherings
 RIKEN Quantum Seminar
 Quantum Computation SG Seminar
 DEEPIN Seminar
 NEW WG Seminar
 LabTheory Standing Talks
 QFTcore Seminar
 STAMP Seminar
 QuCoIn Seminar
 Number Theory Seminar
 BerkeleyiTHEMS Seminar
 iTHEMSRNC Meson Science Lab. Joint Seminar
 AcademicIndustrial Innovation Lecture
 RIKEN Quantum Lecture
 Theory of Operator Algebras
 iTHEMS Intensive CourseEvolution of Cooperation
 Introduction to PublicKey Cryptography
 Knot Theory
 iTHES Theoretical Science Colloquium
 SUURICOOL Seminar
 iTHES Seminar