セミナー

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

Constraining superheavy dark matter with the multi-messenger observations of accompanying radiation

2019年12月20日(金) 14:00 - 15:00

Yana Zhezher (東京大学 宇宙線研究所 (ICRR))

One of the main alternatives for the weakly interacting massive particles (WIMP) dark matter scenario are the super-heavy X particles with masses larger than the weak scale by orders of magnitude. We assume the experimentally more plausible scenario of decaying superheavy dark matter (SHDM), which leads to the production secondary particles: electrons, positrons, gamma rays and neutrinos. The hypothetical X-particle has two main parameters: it’s mass MX and lifetime ?, which can be indirectly constrained by comparisons of predicted flux of secondary particles with the astrophysical observations. We present the limits on the SHDM parameters derived with the multi-messenger data from the Fermi-LAT, IceCube and other experiments.

会場: セミナー室 (132号室)

イベント公式言語: 英語

Scalable Majorana vortex modes in iron-based superconductors

2019年12月18日(水) 13:30 - 15:00

邱 靖凱 (Senior Research Associate, Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, China)

The iron-based superconductor FeTexSe1−x is one of the material candidates hosting Majorana vortex modes residing in the vortex cores. It has been observed by recent scanning tunneling spectroscopy measurement that the fraction of vortex cores possessing zero-bias peaks decreases with increasing magnetic field on the surface of FeTexSe1−x. The hybridization of two Majorana vortex modes cannot simply explain this phenomenon. We construct a three-dimensional tight-binding model simulating the physics of over a hundred Majorana vortex modes in FeTexSe1−x. Our simulation shows that the Majorana hybridization and disordered vortex distribution can explain the decreasing fraction of the zero-bias peaks observed in the experiment; the statistics of the energy peaks off zero energy in our Majorana simulation are in agreement with the experiment.

会場: 研究本館 435-437号室

イベント公式言語: 英語

Multiple Zeta Values: Interrelation of Series and Integrals

2019年12月17日(火) 16:00 - 18:10

山本 修司 (慶應義塾大学 准教授)

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. Abstract: This is an introduction to multiple zeta values (MZVs). Although the study of MZVs is related to various areas of mathematics, we will concentrate on the algebraic structures of MZVs themselves. The key point is that MZVs have two kinds of representations: nested series and iterated integrals. We present how these two representations yield rich algebraic relations among MZVs.

会場: セミナー室 (160号室)

イベント公式言語: 英語

Weak lensing cosmology by Subaru HSC survey

2019年12月12日(木) 10:30 - 12:00

日影 千秋 (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 特任准教授)

Place: IPMU seminar room C

会場: Kavli IPMU 棟

イベント公式言語: 英語

Seminar talk on GRB190114C

2019年12月11日(水) 13:45 - 15:30

井上 進 (理化学研究所 数理創造プログラム (iTHEMS) 研究員)

Detection of very high energy gamma-rays (~TeV) from GRB190114C by MAGIC telescope is reported in the latest nature issue. Dr. Susumu Inoue (iThems) who is one of MAGIC team members will give a seminar talk on this exciting event.

会場: セミナー室 (132号室)

イベント公式言語: 英語

Noncommutative crepant resolutions and some higher dimensional flops

2019年12月4日(水) 16:00 - 18:10

原 和平 (早稲田大学 理工学術院 日本学術振興会特別研究員)

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. Abstract: We will talk about the theory noncommutative resolution of singularities. Noncommutative resolution is a noncommutative analog of usual (geometric) resolution of singularities, and allows us to generalise the idea of McKay correspondence to a large class of singularities. In the first part of the talk, we discuss the classical McKay correspondence, the definition of noncommutative crepant resolution, and some known results in lower dimensions. In the second half, we will discuss some concrete examples of noncommutative crepant resolutions in higher dimensions.

会場: セミナー室 (160号室)

イベント公式言語: 英語

A multiscale study of turbulent heating in hot accretion flows

2019年11月18日(月) 14:00 - 15:00

川面 洋平 (東北大学 助教)

Recently, the Event Horizon Telescope (ETH) collaboration revealed the stunning picture of radiation from the vicinity of the black hole. For accurate interpretation of the observation, it is crucial to understand the nature of plasma in the accretion disk. The disks that EHT is observing are called radiatively inefficient accretion flows, in which the plasma is hot and dilute, and consequently collisionless. In collisionless plasma, ions and electrons can have different temperatures as they do not thermally relax through Coulomb interaction. The ion-to-electron temperature ratio is the key to interpreting the observation because we can measure only the electrons' energy via radiation. To study ion and electron heating, kinetic treatment, rather than hydrodynamic treatment, is necessary. However, kinetic plasma turbulence is an extremely challenging subject. Therefore, we utilized gyrokinetics that is widely used in magnetic confinement fusion research. Our new multiscale approach treats a "large scale" where turbulence is driven by magnetorotational instability via MHD, and a "small scale" where turbulence is dissipated via gyrokinetics. Using this approach, we formulated a prescription of ion-to-electron heating ratio. In my talk, I will also present basic knowledge that is necessary to study collisionless turbulent heating.

会場: セミナー室 (132号室)

イベント公式言語: 英語

Variational methods in quantum annealing

2019年11月15日(金) 13:30 - 15:00

松浦 俊司 (Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)

The rapid progress in the manufacturing of quantum computing hardware has opened up the possibility of exploring its application in solving computationally challenging problems. In this work, we present variational methods in quantum annealing for solving problems more efficiently than the standard adiabatic methods. Important limitations common to all near-term quantum devices include the absence of error correction and the short coherence time, which restrict the computational power of these systems. Therefore, shortening the time taken to perform an individual run of a quantum algorithm and making the annealing process noise resilient is essential for successfully obtaining accurate results. The efficiency of the methods is demonstrated in the ground-state energy estimation of simple molecular systems. Compared with the standard annealing method, the variational algorithms show significant improvements in the annealing time required to achieve a high accuracy.

会場: 研究本館 433号室

イベント公式言語: 英語

Some topics in projective geometry of algebraic varieties

2019年11月8日(金) 16:00 - 18:10

伊藤 敦 (名古屋大学 大学院多元数理科学研究科 助教)

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. Abstract: We talk about Gauss maps and projective dual varieties, which are classical objects in projective geometry of algebraic varieties. In particular, we explain Gauss maps in positive characteristic and projective dual varieties of toric varieties in characteristic 0.

会場: セミナー室 (160号室)

イベント公式言語: 英語

Semiclassical defect measures and observability estimate for Schrödinger operators with homogeneous potentials of order zero

2019年10月30日(水) 8:40 - 10:00

三上 渓太 (理化学研究所 数理創造プログラム (iTHEMS) 研究員)

Seminar will be held from 15:40 to 17:00 on Oct.29(PDT, the U.S. Pacific Daylight Time) as a Harmonic Analysis and Differential Equations Seminar.

会場: UC Berkeley

イベント公式言語: 英語

Atiyah-Hirzebruch spectral sequence in the band theory

2019年10月24日(木) 16:00 - 18:10

塩崎 謙 (京都大学 基礎物理学研究所 助教)

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. Abstract: The topological nature of the band theory in crystalline systems can be well described by the topological K-theory over the Brillouin zone torus. In the first part of my talk, I will present the band-theory understanding of the grading of the K-group, and how the exactness axiom and the Mayer-Vietoris sequence are naturally understood. In the second part, I discuss how to compute the differentials of the Atiyah-Hirzebruch spectral sequence associated with a cell decomposition.

会場: セミナー室 (160号室)

イベント公式言語: 英語

力学系の平均次元と情報理論

2019年10月21日(月) - 23日(水)

塚本 真輝 (九州大学 教授)

Oct.21 15:30-16:30, 16:40-17:40, Okochi Hall Oct.22 13:30-14:30, room #435-437, Main Research Building Oct.23 13:30-14:30, room #435-437, Main Research Building

会場: 大河内記念ホール / 研究本館 435-437号室

イベント公式言語: 日本語

Haloes at the low-mass end in wino dark matter

2019年10月21日(月) 13:00 - 15:00

関口 豊和 (東京大学 ビッグバン宇宙国際センター (RESCEU))

Neutral wino is a natural candidate of dark matter in split-supersymmetry. Indirect detection is a promising probe of wino dark matter, with its annihilation enhanced non-perturvatively (i.e. Sommerfeld enhancement). In theoretical prediction, halo formation at the low-mass end is a key ingredient. For this purpose, we investigate kinetic decoupling of wino dark matter and consequent dark matter density perturbations. We show that inelastic processes involving charged wino, which are relevant for kinetic equilibrium at late times, shuts off abruptly. This results in boosted acoustic peaks in density power spectrum at horizon scales around the kinetic decoupling. Based on an analytic modeling of subhalo evolution, we estimate the subhalo mass function of (dwarf) galaxy-sized haloes and effects on the annihilation boost factor. We also discuss application of our analysis to SU(2)_L multiplet minimal dark matter.

会場: セミナー室 (160号室)

イベント公式言語: 英語

Introduction to 1QBit Open Software QEMIST "Quantum-Enabled Molecular ab Initio Simulation Toolkit"

2019年10月17日(木) 13:30 - 15:00

松浦 俊司 (Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)

会場: 研究本館 433号室

イベント公式言語: 英語

Dark matter search in extended dwarf spheroidal galaxies with CTA

2019年10月11日(金) 14:00 - 15:00

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

The nature of dark matter (DM) is still a big mystery. Among the varieties of candidates, Weakly Interacting Massive Particle (WIMP) is one of the most promising ones. Gamma-ray observations of dwarf spheroidal galaxies (dSphs) by Fermi satellites put the strongest constraints at mDM<~ a few hundreds of GeV. In the near future, Cherenkov Telescope Array (CTA) starts its operations and expect to probe WIMP of mDM>~O(1)TeV. Different from previous experiments, spatial distributions of DM in dSphs are resolved with CTA. In this talk, I explain how it affects our accessibility to DM annihilation cross-section.

会場: セミナー室 (132号室)

イベント公式言語: 英語