セミナー

Gradient Flow Equation and Its Applications

2020年5月15日(金) 13:30 - 15:00

菊地 健吾 (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

Gradient flow is the one of the methods to suppress the ultraviolet divergence in gauge theories. The any correlation functions in terms of the flowed field, which is defined by the gradient flow equation, are finite without additional renormalizations. Because of this surprising property, the methods has been studied widely, especially in the lattice field theory. In this seminar, we introduce what the gradient flow is briefly. And we show our work, “generalized gradient flow equation”, which is the gradient flow equation for field theories with nonlinearly realized symmetry. Applying the formalism to a supersymmetric theory and O(N) non linear sigma model, we obtain the SUSY gradient flow and the Large N gradient flow. We also refer to the current research, the gradient flow of the supersymmetric theory with the non-renormalization theorem and the new formalism to obtain the sphalerons, which is one of the static classical solutions, using gradient flow methods, if time allows.

会場: via Zoom

イベント公式言語: 英語

How many electrons can atoms bind?

2020年5月13日(水) 16:00 - 18:10

後藤 ゆきみ (理化学研究所 数理創造プログラム (iTHEMS) 基礎科学特別研究員)

In this talk, I will introduce the mathematical studies on the ionization problem. Some experimental & numerical evidences say that any doubly charged atomic ion X^{2-} is not stable. This 'fact' is called the ionization conjecture in mathematical physics literatures. My hope is to illustrates the interplay between mathematical and physical ideas. The talk is directed towards researchers on various aspects of quantum mechanics. In the first part, we will discuss the many-body aspects of quantum mechanics and introduce some basic notions. The second part will deal with the mathematical results in some approximation theories.

会場: via Zoom

イベント公式言語: 英語

Models to describe how virus spreads in vitro

2020年5月13日(水) 10:00 - 10:45

カトゥリン・ボシゥメン (理化学研究所 数理創造プログラム (iTHEMS) 客員主管研究員 / Professor, Department of Physics, Ryerson University, Canada)

This is meant as an introductory talk about my research field, virophysics, in which I apply the rigour and methods of physics to study virology. My focus is primarily in vitro (how virus spreads cell-to-cell in a cell culture) but I occasionally do some in vivo work. Recently, my hobby became tracking COVID-19 spread.

会場: via Zoom

イベント公式言語: 英語

Slip or (k)not: Geometry and mechanical performance of physical knots

2020年5月7日(木) 17:00 - 17:45

佐野 友彦 (PD, École polytechnique fédérale de Lausanne, Switzerland)

Knots can impart unique mechanical function to filamentary structures, with examples ranging across length scales, including DNA, polymer-chains, shoelaces, climbing ropes, tennis racket, and surgical sutures. Even though knot theory has a long history of studies in the realm of mathematics, mechanics-based studies of physical knots are much rarer. The fundamental challenge in the understanding of their mechanics under a wide range of loading conditions stems from the fact that their topology, geometry, elasticity, and friction are all tangled ingredients. In this talk, combining experiments, simulations and theory, we present the recent progress on the predictive framework for the knot performance.

会場: via Zoom

イベント公式言語: 英語

From Eigenvalues to Resonances

2020年5月1日(金) 16:00 - 18:10

三上 渓太 (理化学研究所 数理創造プログラム (iTHEMS) 研究員)

Resonance is one of the most studied object in mathematical study of Schrödinger operators. One possible reason is that resonance is appeared in many other fields like arithmetic, physics, and topography. This series of talks target both mathematicians and researchers in other fields. The goal of the talk is to introduce the study of resonances for two body Schrödinger operators. In the first part, we briefly review spectral theory and how we use it in the study of Schrödinger operators. The aim of this part is to introduce the audience some basic notions used in the study of Schrödinger operators. In the second part, we give brief introduction of resonances and its application to both mathematicians and researchers in other fields. We start from mathematical definition of resonances to its applications in the other fields.

会場: via zoom

イベント公式言語: 英語

Analyses of large-scale sequence data from “PROTIST” can reveal the eukaryotic phylogeny and evolution

2020年4月30日(木) 10:00 - 10:45

矢﨑 裕規 (理化学研究所 数理創造プログラム (iTHEMS) 特別研究員)

Most of the phylogenetic diversity of eukaryotes is made up of unicellular eukaryotic microorganisms called protists, some of which have not known phylogenetic home (called Orphans). Orphans are likely to hold important keys to the evolution of eukaryotes. In this seminar, I will introduce present case studies that reveal phylogenetic home and organelle evolution of orphan protists through sequence analysis based on large-scale sequence data.

会場: via Zoom

イベント公式言語: 英語

Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

2020年4月27日(月) 16:00 - 17:00

Sylvia Zhu (Postdoctoral Researcher, Deutsches Elektronen-Synchrotron DESY, Germany)

Bosons such as axions or axion-like particles can form enormous clouds around black holes via the superradiance instability. As the bosons annihilate in the presence of the black hole, they produce a long-lived, slowly-evolving continuous gravitational-wave signal that is potentially detectable using the current generation of gravitational-wave interferometers.A non-detection can disfavor the existence of axions in certain mass ranges, although this is highly dependent on the Galactic black hole population. In this talk, I will discuss the expected annihilation signal from the population of isolated stellar-mass black holes in the Galaxy, and the prospects for detecting the signal using standard searches for continuous gravitational waves.

会場: via Zoom

イベント公式言語: 英語

Social evolution in viruses

2020年4月22日(水) 10:00 - 10:45

アッシャー・リークス (理化学研究所 数理創造プログラム (iTHEMS) 国際プログラム・アソシエイト / Ph.D. Student, Department of Zoology, University of Oxford, UK)

Viruses are normally thought of as solitary organisms. However, in reality viruses often interact with one another, and these interactions can have important consequences for how viruses evolve and cause disease. In this talk, I will show how simple models of virus-virus interactions can help us to understand some puzzling aspects of virus biology. At the end, I will also talk about a new modelling project on Covid-19 joint with Ryosuke, which considers how human actions such as social distancing could influence the evolution of virulence.

会場: via Zoom

イベント公式言語: 英語

Holography from field theories: a realization of AdS/CFT correspondence and beyond

2020年3月18日(水) 13:30 - 14:30

青木 愼也

*Seminar room changed from 160 to 433. We argue that the Anti-de-Sitter (AdS) geometry in $d+1$ dimensions naturally emerges from an arbitrary conformal field theory in $d$ dimensions using the free flow equation. We first show that an induced metric defined from the flowed field generally corresponds to the quantum information metric, called the Bures or Helstrom metric, if the flowed field is normalized appropriately. We next verify that the induced metric computed explicitly with the free flow equation always becomes the AdS metric when the theory is conformal. We also show that the conformal symmetry in $d$ dimensions converts to the AdS isometry in $d+1$ dimensions after $d$ dimensional quantum averaging. This guarantees the emergence of AdS geometry without explicit calculation. We next apply this method to non-relativistic systems with anisotropic scaling symmetries, such as Lifshitz field theories and Schr\”odinger invariant theories. In consequence we obtain a new hybrid geometry of Lifshitz and Schr\”odinger spacetimes as a general holographic geometry. We also show that the bulk hybrid geometry is realized by an Einstein-Maxwell-Higgs system plus a gauge fixing term for diffeomorphism, which may be interpreted as a holographic dual of a general non-relativistic system at the boundary.

会場: 研究本館 433号室

イベント公式言語: 日本語

Index of the Wilson-Dirac operator revisited: a discrete version of Dirac operator on a finite lattice

2020年2月25日(火) 16:00 - 18:10

古田 幹雄 (東京大学 教授)

The Wilson-Dirac operator is a discrete version of Dirac operator defined on regular lattices. When the discrete version is a fine approximation of the Dirac operator on a Z/2-graded Clifford module on a torus, it is known that (1) an integer-valued index is defined for the Wilson-Dirac operator, and (2) the index is equal to the Atiyah-Singer index of the Dirac operator on the torus. These have been well established up to around 2000. The strategy of all the previous works is to make use of the discrete version of the heat kernel for Neuberger's overlap Dirac operator. Therefore the strategy cannot be generalized to mod 2 index nor family version of index. In this talk I would like to explain a new approach to the index of Wilson-Dirac operator which can be immediately generalized to these various cases. Joint work with H. Fukaya, S. Matsuo, T. Onogi, S. Yamaguchi and M. Yamashita.

会場: セミナー室 (160号室)

イベント公式言語: 英語

Mining for Dark Matter substructure: Learning from lenses without a likelihood

2020年2月17日(月) 14:00 - 15:30

Johann Brehmer (Postdoctoral Researcher, New York University, USA)

Dr. Brehmer gives us a talk about a method to deduce DM small structures. Please join us! The subtle imprint of dark matter substructure on extended arcs in strong lensing systems contains a wealth of information about the small-scale distribution of dark matter and, consequently, about the underlying particle physics. However, teasing out this effect is challenging since the likelihood function for realistic simulations of population-level parameters is intractable. Structurally similar problems appear in many other scientific fields ranging from particle physics to neuroscience to epidemiology, which has prompted the development of powerful simulation-based inference techniques based on machine learning. We give a broad overview over these methods, and then apply them to the problem of substructure inference in galaxy-galaxy strong lenses. In this proof-of-principle application to simulated data, we show that these methods can provide an efficient and principled way to simultaneously analyze an ensemble of strong lenses, and can be used to mine the large sample of lensing images deliverable by near-future surveys for signatures of dark matter substructure.

会場: 研究本館 424-426号室

イベント公式言語: 英語

Solved and open problems regarding the neighborhood grid data structure

2020年2月7日(金) 16:00 - 18:10

スクロツキ マーティン (理化学研究所 数理創造プログラム (iTHEMS) 客員研究員 / Fellow, German Academic Scholarship Foundation, Germany)

2020年2月7日 16:00-17:00 17:10-18:10

会場: セミナー室 (160号室)

イベント公式言語: 英語

Biology Talk

2020年2月5日(水) 16:00 - 16:30

安井 康夫 (京都大学 農学研究科 助教)

京都大学農学部の安井康夫先生に、中国雲南省での採集を含むソバの研究プロジェクトについて20-30分程度で紹介してもらいます。興味のある方はぜひお越しください。

会場: セミナー室 (160号室)

イベント公式言語: 日本語

ABBL/iTHEMS seminar - talk on ultra-high energy cosmic rays

2020年1月31日(金) 14:00 - 15:00

木戸 英治 (理化学研究所 開拓研究本部 (CPR) 長瀧天体ビッグバン研究室)

会場: セミナー室 (132号室)

イベント公式言語: 英語

Nucleon Structure from Quantum Chromodynamics

2020年1月30日(木) 11:00 - 12:00

張 家丞 (理化学研究所 数理創造プログラム (iTHEMS) 研究員 / LBNL/UCB, USA)

Talk of this seminar is a colloquium style, so that non-expert can enjoy. Please feel free to join. The origin of matter is one of the longest standing mysteries that have captured the human imagination. The modern description of particle and nuclear physics hypothesizes that our matter filled universe must have resulted in the underlying physical processes favoring the preservation of matter over antimatter during the initial formation of our universe. This mechanism is attributed to the fundamental breaking of particle and antiparticle symmetry in physics beyond the Standard Model. One source of asymmetry is hypothesized to reside in the neutrino sector, and intense international efforts are being pursued to observe this phenomena in neutrino scattering experiments. Precise interpretation of experimental observations benefits from a Standard Model prediction of how nuclear matter interacts with neutrinos. The modern theory governing matter and their properties is the theory of the strong interaction, quantum chromodynamics (QCD). In this talk I will discuss a QCD calculation of the nucleon form factor at zero momentum transfer, which is related to how a neutrino at rest interacts with a single proton or neutron, followed by current progress on the calculation of the proton radius which is related to the slope of the form factor. Together the calculations paves a novel way forward towards a precise determination of the nucleon form factor up to momentum transfer relevant for neutrino scattering. I will end the talk by discussing future milestones and challenges as we work towards calculations for nuclear physics starting from QCD.

会場: 研究本館 433号室

イベント公式言語: 英語

ABBL/iTHEMS seminar - talk on neutron stars

2020年1月24日(金) 14:00 - 15:00

祖谷 元 (理化学研究所 数理創造プログラム (iTHEMS) 研究員 / 理化学研究所 開拓研究本部 (CPR) 長瀧天体ビッグバン研究室 研究員)

会場: セミナー室 (132号室)

イベント公式言語: 英語

Semiclassical methods in mathematical quantum mechanics

2020年1月23日(木) 16:00 - 18:10

中村 周 (学習院大学 教授)

Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for non-mathematicians. After a short break, the second 60 minutes is spent for a bit more detailed talk for mathematicians (working in other areas). We welcome you joining both parts of the seminar or only the first/second half. Talk 1: Semiclassical analysis, microlocal analysis and scattering theory. I plan to talk about overview on the semiclassical analysis and related topics, especially its intrinsic relationship with microlocal analysis and (microlocal) scattering theory. Roughly speaking, the microlocal analysis is an application of semiclassical idea to the analysis of singularities, and its analogue in momentum space is the microlocal scattering theory. We discuss basic notions of these, and mention several recent results. Talk 2: Microlocal structure of the scattering matrix with long-range perturbations. As an example of topics discussed in Talk 1, we discuss recent results on the scattering matrix with long-range perturbations. In particular, we show that the scattering matrix is expressed as a Fourier integral operator, and in some cases we can decide its spectral properties. Our approach is fairly geometric and abstract, and thus applies not only to usual Schrödinger operators but also to higher order operators and discrete Schrödinger operators.

会場: 研究本館 435-437号室

イベント公式言語: 英語

Tipping point detection of nonlinear dynamics by dynamic network biomarkers, and short-term time-series data prediction by randomly distributed embedding

2020年1月15日(水) 14:00 - 16:30

Luonan Chen (Professor, Excutive director, Chinese Academy of Sciences, China)

He will talk about theoretical study on complex network data, including clinical data. His talk consists of two parts: 14:00-15:00: Detecting the tipping points of dynamic processes by dynamic network biomarkers 15:00-15:30: Coffee break 15:30-16:30: Predicting future dynamics of short-term time-series data by randomly distributed embedding First part of his talk is for general audience. In second part of his talk, he will explain mathematical basis of his study in detail.

会場: 統合支援施設（第一食堂） 2階 大会議室

イベント公式言語: 英語

Particle acceleration in young supernova remnants with X-ray and gamma-ray observations

2020年1月9日(木) 10:00 - 11:00

辻 直美

A supernova remnant (SNR) is a prominent candidate as an accelerator of galactic cosmic rays. In a widely accepted theory of diffusive shock acceleration, a particle is accelerated by diffusing back and forth across shock waves. The spectral cutoff shape of accelerated electrons is determined by diffusion and cooling and appears in the X-ray and TeV gamma-ray energy ranges, respectively, through synchrotron radiation and inverse Compton scattering. To measure the cutoff shape precisely and explore the corresponding diffusion coefficient and acceleration efficiency, we systematically analyze young SNRs that emit nonthermal X-rays and TeV gamma-rays. We found a variety of particle acceleration depending on individual SNRs: the cutoff energy is well-reproduced by the theoretical prediction in Kepler’s SNR and Tycho’s SNR, while it might be affected by the surroundings in Cassiopeia A and SN 1006. Putting all the eleven SNRs analyzed in this study together, the acceleration tends to be more efficient as the SNR evolves and becomes older, which implies a connection with turbulent production.

会場: セミナー室 (160号室)

イベント公式言語: 英語

第32回 QCD Club

2019年12月26日(木) 15:00 - 17:00

タイトル : 磁性体におけるワイル粒子の巨大応答とその制御に向けて 概要：近年、物性分野において、高エネルギー分野のトピックスがホットな話題となることが多い。特に、最近のワイル粒子の研究はその顕著な例である。21世紀に入り、物性分野においてトポロジーの重要性の認識とともに、トポロジカル絶縁体などの新しい量子相がいくつも発見されてきたが、最近、特に注目を浴びているのが、3次元のギャップレス相であるワイル半金属と呼ばれる物質群である。ワイル半金属は、空間反転対称性を持たないクラスと時間反転対称性を持たないクラスの二つに分けられる。本講演では、一般的な物性分野の研究紹介を最初に簡単にさせていただいたのちに、後者に属するワイル金属磁性体に着目した話題を詳しく紹介する。特に我々の研究グループが近年進めているワイル粒子の示す応答、例えば、異常ホール効果、異常ネルンスト効果、カイラル異常の研究に加えて、時間が許せばその応用の可能性についても述べる。さらに、磁性体の強みは磁場等の外場で磁性を制御できることであり、それに基づいたワイル粒子の制御の可能性ついても触れる。物性分野の強みは、多角的な実験が可能で、理論と実験が両輪として常にお互いの確認を取りながら進歩できるということである。一方で、一つの現象に様々な自由度が複雑に絡み合っている可能性があり、単純化したモデルで本質を捉えることが難しい場合も多い。そのあたりについても触れながら、様々な事例をご紹介したい。

イベント公式言語: 日本語