Seminar
656 events

Scalable Majorana vortex modes in ironbased superconductors
December 18 (Wed) at 13:30  15:00, 2019
ChingKai Chiu (Senior Research Associate, Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, China)
The ironbased 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 zerobias 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 threedimensional tightbinding 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 zerobias peaks observed in the experiment; the statistics of the energy peaks off zero energy in our Majorana simulation are in agreement with the experiment.
Venue: #435437, Main Research Building
Event Official Language: English

Multiple Zeta Values: Interrelation of Series and Integrals
December 17 (Tue) at 16:00  18:10, 2019
Syuji Yamamoto (Associate Professor, Keio University)
Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for nonmathematicians. 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.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Weak lensing cosmology by Subaru HSC survey
December 12 (Thu) at 10:30  12:00, 2019
Chiaki Hikage (Project Associate Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)
Place: IPMU seminar room C
Venue: Kavli IPMU Building
Event Official Language: English

Seminar talk on GRB190114C
December 11 (Wed) at 13:45  15:30, 2019
Susumu Inoue (Research Scientist, iTHEMS)
Detection of very high energy gammarays (~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.
Venue: Seminar Room #132
Event Official Language: English

Seminar
Noncommutative crepant resolutions and some higher dimensional flops
December 4 (Wed) at 16:00  18:10, 2019
Wahei Hara (JSPS Research Fellow, School of Science and Engineering, Waseda University)
Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for nonmathematicians. 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.
Venue: Seminar Room #160
Event Official Language: English

Seminar
A multiscale study of turbulent heating in hot accretion flows
November 18 (Mon) at 14:00  15:00, 2019
Yohei Kawazura (Assistant Professor, Tohoku University)
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 iontoelectron 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 iontoelectron heating ratio. In my talk, I will also present basic knowledge that is necessary to study collisionless turbulent heating.
Venue: Seminar Room #132
Event Official Language: English

Variational methods in quantum annealing
November 15 (Fri) at 13:30  15:00, 2019
Shunji Matsuura (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 nearterm 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 groundstate 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.
Venue: #433, Main Research Building
Event Official Language: English

Seminar
Some topics in projective geometry of algebraic varieties
November 8 (Fri) at 16:00  18:10, 2019
Atsushi Ito (Assistant Professor, Graduate School of Mathematics, Nagoya University)
Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for nonmathematicians. 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.
Venue: Seminar Room #160
Event Official Language: English

Semiclassical defect measures and observability estimate for Schrödinger operators with homogeneous potentials of order zero
October 30 (Wed) at 8:40  10:00, 2019
Keita Mikami (Research Scientist, iTHEMS)
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.
Venue: UC Berkeley
Event Official Language: English

Seminar
AtiyahHirzebruch spectral sequence in the band theory
October 24 (Thu) at 16:00  18:10, 2019
Ken Shiozaki (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
Plan of the seminar: we separate each talk into two. In the first 60 minutes the speaker gives an introductory talk for nonmathematicians. 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 Ktheory over the Brillouin zone torus. In the first part of my talk, I will present the bandtheory understanding of the grading of the Kgroup, and how the exactness axiom and the MayerVietoris sequence are naturally understood. In the second part, I discuss how to compute the differentials of the AtiyahHirzebruch spectral sequence associated with a cell decomposition.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Mean dimension of dynamical systems and information theory
October 21 (Mon)  23 (Wed), 2019
Masaki Tsukamoto (Professor, Kyushu University)
Oct.21 15:3016:30, 16:4017:40, Okochi Hall Oct.22 13:3014:30, room #435437, Main Research Building Oct.23 13:3014:30, room #435437, Main Research Building
Venue: Okochi Hall / #435437, Main Research Building
Event Official Language: Japanese

Seminar
Haloes at the lowmass end in wino dark matter
October 21 (Mon) at 13:00  15:00, 2019
Toyokazu Sekiguchi (Research Center for the Early Universe (RESCEU), The University of Tokyo)
Neutral wino is a natural candidate of dark matter in splitsupersymmetry. Indirect detection is a promising probe of wino dark matter, with its annihilation enhanced nonperturvatively (i.e. Sommerfeld enhancement). In theoretical prediction, halo formation at the lowmass 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) galaxysized haloes and effects on the annihilation boost factor. We also discuss application of our analysis to SU(2)_L multiplet minimal dark matter.
Venue: Seminar Room #160
Event Official Language: English

Introduction to 1QBit Open Software QEMIST "QuantumEnabled Molecular ab Initio Simulation Toolkit"
October 17 (Thu) at 13:30  15:00, 2019
Shunji Matsuura (Fundamental Researcher, Quantum Simulation Division, 1QBit, Canada)
Venue: #433, Main Research Building
Event Official Language: English

Dark matter search in extended dwarf spheroidal galaxies with CTA
October 11 (Fri) at 14:00  15:00, 2019
Nagisa Hiroshima (Postdoctoral Researcher, iTHEMS)
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. Gammaray 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 crosssection.
Venue: Seminar Room #132
Event Official Language: English

Seminar
Finite N corrections to the superconformal index from D3brane analysis in AdS_5/CFT_4
October 8 (Tue) at 15:30  17:00, 2019
Reona Arai (Ph.D. Student, Tokyo Institute of Technology)
In the context of the AdS/CFT, the Type IIB superstring theory on AdS_5 \times SE_5 corresponds to an N=1 quiver gauge theory, where SE_5 is a fivedimensional SasakiEinstein manifold. We study this correspondence by using the superconformal index, which contains the information of the BPS spectrum in the theory. It is known that the index of the large N limit is evaluated by the KaluzaKlein modes on SE_5 and the agreement with CFT results was confirmed in many examples. In this talk, we consider the finite N corrections to the index on the gravity side as a next step. To do this, we focus on a single D3brane wrapped around a threecycle on SE_5. Because there are in general several threecycles on SE_5, we need to sum up contributions of these single D3branes. By using the D3brane analysis, we propose a prescription to calculate the finite N corrections to the index. We explain our prescription through some examples and see the agreement with the CFT results calculated by the localization method.
Venue: Seminar Room #160
Event Official Language: English

A new lamppost in dark matter searches: Composite Dark Matter
October 1 (Tue) at 10:00  18:00, 2019
Enrico Rinaldi (Research Parttime Worker Ⅰ, iTHEMS)
In the search for the nature of dark matter many particle physics models are proposed. Models originating from a new strongly coupled dark sector, similar to QCD and Nuclear Physics, give rise to Composite Dark Matter particles. These models are hard to study, but they have a very interesting phenomenology with clear signals that are distinct from the usual WIMP candidates. To make robust predictions in Composite Dark Matter models one often needs to investigate nonperturbative effects due to the strong dynamics. In my talk I will explain how Lattice Field Theory methods and numerical simulations are well suited for this task and contribute to a solid uncertainty quantification. A variety of detection signals can be studied with lattice simulations, from dark matter self interactions to interactions with regular matter and even signals of dark phase transitions generating primordial gravitational waves.
Venue: #424426, Main Research Building
Event Official Language: English

Seminar
Angular power spectrum analysis on current and future highenergy neutrino data
September 18 (Wed) at 14:00  15:00, 2019
Ariane Dekker (Faculty of Science, University of Amsterdam, Netherlands)
The astrophysical neutrino events that have been measured in the last couple of years show an isotropic distribution on the sky. To constrain the contribution of source populations to the observed neutrino sky, we consider isotropic and anisotropic components of the diffuse neutrino data. We simulate throughgoing muon neutrino events by applying statistical distributions for the fluxes of extragalactic sources and investigate the sensitivities of current (IceCube) and future (IceCubeGen2 and KM3NeT) experiments. I will show that the angular power spectrum is a powerful probe to assess the angular characteristics of neutrino data and demonstrate that we are already constraining rare and bright sources with current IceCube data. In addition, I will investigate the decay and annihilation of very heavy dark matter as a potential neutrino source suggested by the excess in HESE data. We apply our angular power spectrum analysis to HESE data for different channels, allowing us to interpret the observed neutrino sky and perform a sensitivity forecast.
Venue: #160, 1F, Main Research Building
Event Official Language: English

Seminar
iTHEMS Biology Seminar
September 13 (Fri) at 15:00  17:20, 2019
Hiroyuki Kubota (Professor, Medical Institute of Bioregulation, Kyushu University)
Yasufumi Uezu (Researcher, Sensory And Motor Research Group, NTT Communication Science Laboratories)Timetable 15:0016:00 Hiroyuki Kubota (Kyushu Univ.) 16:0016:20 Break 16:2017:20 Yasufumi Uezu (NTT) Time: 15:0016:00 Speaker: Hiroyuki Kubota (Kyushu Univ.) Title: Regulation of insulin action by temporal patterns of insulin Abstract: Cells respond to various extracellular stimuli through a limited number of signaling pathways. One strategy to process such stimuli is to code the information into the temporal patterns of molecules. Almost all hormones exhibit distinct temporal patterns and the importance of their patterns has been reported. However, the mechanisms of how hormones regulate downstream molecules depending on their temporal patterns remain unknown. We focused on insulin which plays crucial roles on glucose homeostasis and shows several temporal patterns in vivo. In this study, we show how the Insulin signaling pathway processes the information encoded into the temporal patterns of blood insulin using a cultured cell line and mice. We found that insulin patterns selectively regulate the insulinAKT pathway, metabolites, and mRNAs. Mathematical modeling revealed the mechanisms via differences in network structures and from sensitivity and time constants. Given that almost all hormones exhibit distinct temporal patterns, temporal coding may be a general principle of system homeostasis by hormones. Time: 16:2017:20 Speaker: Yasufumi Uezu (NTT) Title: Sourcefilter interaction brings various representation in speech and singing voice Abstract: Speech plays a very important role in human communication. The sourcefilter interaction, a model that takes into account the actual speech production process, assumes that the sound source generation mechanism and the vocaltract filter are not independent, but affect each other physiologically and acoustically. It is known that the sourcefilter interaction brings about nonlinearity of speech and singing, such as singing voice with a loud volume and wide pitch range like an opera singer, or voice register transition where the vocal suppression and/or the voice pitch jump occurs. I would like to introduce my researches targeting nonlinear vocalization phenomena due to the sourcefilter interaction and results of measuring and analyzing the time waveform of speech sound and vocalfold vibrations through measurement experiments.
Venue: #424426, Main Research Building
Event Official Language: Japanese

Seminar
Introduction to quantum manybody system
September 5 (Thu)  6 (Fri), 2019
Hosho Katsura (Associate Professor, Department of Physics, Graduate School of Science, The University of Tokyo)
Venue: #535537, Main Research Building / #435437, Main Research Building
Event Official Language: Japanese

Introduction to Quantum Annealing: from Fundamentals to Applications
September 2 (Mon)  3 (Tue), 2019
Hirotaka Irie (Visiting Scientist, iTHEMS / Assistant Manager, DENSO Corporation)
Sep. 2 (Mon) 10:3012:00, 13:3015:00, 15:3017:00 Lecture 1: What is quantum annealing and quantum computation? Lecture 2: Quatum Ising models as fluxqubit degree of freedom Lecture 3: Basic usage of quantum annealer Sep. 3 (Tue) 10:3012:00, 13:3015:00, 15:3017:00 Lecture 4: Optimization problems and computational complexity Lecture 5: Realworld applications Lecture 6: Some other topics Room: 435437 (main research building): Sep.2 (Mon) am 424426 (main research building): Sep.2 (Mon) pm & Sep.3 (Tue) am+pm Abstract: Quantum annealing is a quantumcomputational scheme which tackles computationally hard optimization problems. Its quantummechanically implemented machine, called quantum annealer, is commercially manufactured by DWave Systems, Inc., and is currently available with more than 2000 quantum bits. In this twoday lecture, I would like to discuss fundamental aspects of quantum annealing (1st day) and its realworld applications (2nd day). In particular, I try to overview the current status of the machine and several problems which we should theoretically overcome. In the first day, I will start with discussing what is quantum annealing and then review how quantum Ising model is implemented with fluxqubit degree of freedom. Later on, I will discuss the basic usage of the quantum annealer as a preparation for applications. In the second day, I will first summarize several classes of optimization problems and their computational complexity, and then discuss examples of realworld applications of quantum annealing. Finally, if I have enough time, I would like to discuss other related topic on quantum annealing.
Venue: #435437, Main Research Building / #424426, Main Research Building
Event Official Language: English
656 events
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