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 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.

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 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.

Venue: #433, Main Research Building

Event Official Language: English

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 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.

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

Atiyah-Hirzebruch 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 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.

Venue: Seminar Room #160

Event Official Language: English

Mean dimension of dynamical systems and information theory

October 21 (Mon) - 23 (Wed), 2019

Masaki Tsukamoto (Professor, Kyushu University)

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

Venue: Okochi Hall / #435-437, Main Research Building

Event Official Language: Japanese

Haloes at the low-mass 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 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.

Venue: Seminar Room #160

Event Official Language: English

Introduction to 1QBit Open Software QEMIST "Quantum-Enabled 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. 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.

Venue: Seminar Room #132

Event Official Language: English

Finite N corrections to the superconformal index from D3-brane 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 five-dimensional Sasaki-Einstein 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 Kaluza-Klein 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 D3-brane wrapped around a three-cycle on SE_5. Because there are in general several three-cycles on SE_5, we need to sum up contributions of these single D3-branes. By using the D3-brane 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 Part-time 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 non-perturbative 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: #424-426, Main Research Building

Event Official Language: English

Angular power spectrum analysis on current and future high-energy 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 through-going muon neutrino events by applying statistical distributions for the fluxes of extra-galactic sources and investigate the sensitivities of current (IceCube) and future (IceCube-Gen2 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

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 15:00-16:00 Hiroyuki Kubota (Kyushu Univ.) 16:00-16:20 Break 16:20-17:20 Yasufumi Uezu (NTT) Time: 15:00-16:00 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 insulin-AKT 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: 16:20-17:20 Speaker: Yasufumi Uezu (NTT) Title: Source-filter interaction brings various representation in speech and singing voice Abstract: Speech plays a very important role in human communication. The source-filter interaction, a model that takes into account the actual speech production process, assumes that the sound source generation mechanism and the vocal-tract filter are not independent, but affect each other physiologically and acoustically. It is known that the source-filter interaction brings about non-linearity 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 non-linear vocalization phenomena due to the source-filter interaction and results of measuring and analyzing the time waveform of speech sound and vocal-fold vibrations through measurement experiments.

Venue: #424-426, Main Research Building

Event Official Language: Japanese

Introduction to quantum many-body system

September 5 (Thu) - 6 (Fri), 2019

Hosho Katsura (Associate Professor, Department of Physics, Graduate School of Science, The University of Tokyo)

Venue: #535-537, Main Research Building / #435-437, 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) 10:30-12:00, 13:30-15:00, 15:30-17:00 Lecture 1: What is quantum annealing and quantum computation? Lecture 2: Quatum Ising models as flux-qubit degree of freedom Lecture 3: Basic usage of quantum annealer Sep. 3 (Tue) 10:30-12:00, 13:30-15:00, 15:30-17:00 Lecture 4: Optimization problems and computational complexity Lecture 5: Real-world applications Lecture 6: Some other topics Room: 435-437 (main research building): Sep.2 (Mon) am 424-426 (main research building): Sep.2 (Mon) pm & Sep.3 (Tue) am+pm Abstract: Quantum annealing is a quantum-computational scheme which tackles computationally hard optimization problems. Its quantum-mechanically implemented machine, called quantum annealer, is commercially manufactured by D-Wave Systems, Inc., and is currently available with more than 2000 quantum bits. In this two-day lecture, I would like to discuss fundamental aspects of quantum annealing (1st day) and its real-world 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 flux-qubit 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 real-world applications of quantum annealing. Finally, if I have enough time, I would like to discuss other related topic on quantum annealing.

Venue: #435-437, Main Research Building / #424-426, Main Research Building

Event Official Language: English

Physics of Gamma-Ray Bursts: Emission Mechanism, Particle Acceleration, Nucleosynthesis, and Gravitational Waves

August 17 (Sat) at 12:00 - 13:00, 2019

Shigehiro Nagataki (Deputy Program Director, iTHEMS / Chief Scientist, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

Gamma-Ray Bursts (GRBs) are very powerful, special explosions of massive stars. In the explosions, highly relativistic jets are launched from progenitor stars and lots of gamma-rays are emitted from the jets. It is also suggested by gravitational wave detection with follow-up observations that (short duration) GRBs are triggered by neutron star mergers (NSMs). In this talk, physics of GRBs are introduced with some of our recent studies. I would like to introduce how the relativistic jets will emit bunch of gamma-rays, and how particle acceleration happens in the relativistic jets. I also would like to introduce our recent studies on r-process nucleosynthesis & gravitational wave emission at NSMs. Location: 50A-5132

Venue: Lawrence Berkeley National Laboratory (Berkeley, California)

Event Official Language: English

Complex analysis on a neighborhood of a complex submanifold and its applications

July 30 (Tue) at 16:00 - 18:10, 2019

Takayuki Koike (Lecturer, Department of Mathematics, Graduate School of Science, Osaka City University)

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 explain our recent study on the complex analytic structure of a small tubular neighborhood of a complex submanifold, which is based on T. Ueda's classification theory. We also explain how to apply them to: (i) a study on (non-) existence of a smooth Hermitian metric on a nef line bundle over a projective manifold with semi-positive curvature, and (ii) a study on non-projective and non-Kummer K3 surfaces.

Venue: Seminar Room #160

Event Official Language: English

Introduction to magnitude of metric spaces

July 22 (Mon) at 13:00 - 15:00, 2019

Genki Ouchi (Special Postdoctoral Researcher, iTHEMS)

Leinster introduced the notion of magnitude of a metric space. It is a real number measuring the effective number of points in a metric space. In this talk, I will review generalizations of metric spaces (e.g. asymmetric metric spaces). After that, I would like to talk about the definition, examples and fundamental properties of magnitude.

Venue: Seminar Room #160

Event Official Language: English

Introduction to Schroedinger Operators

July 12 (Fri) at 16:00 - 18:10, 2019

Keita Mikami (Research Scientist, iTHEMS)

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: In this seminar, I will talk about mathematical study of Schroedinger operators (or Schroedinger equation). Part 1: I will talk about what mathematicians do to find a solution to Schroedinger equation. The goal of the first part is to be able to check the existence of solutions of Schroedinger equations in terms of decay/growth rate of potentials. Part 2: I will talk about what can we say about solutions to Schroedinger equation constructed in the first part. Especially, the relationship to the corresponding classical mechanic is introduced.

Venue: Seminar Room #160

Event Official Language: English

Large scale dynamics of integrable systems

July 12 (Fri) at 16:00 - 17:00, 2019

Takato Yoshimura (King's college London, UK)

Hydrodynamics has been a universal tool to study the large scale (long-wavelength) dynamics of interacting many-body systems. It had not been, however, applied to integrable systems until 2016 when two papers, one of which is ours [Physical Review X 6 (4), 041065, (2016)], provided a first legitimate hydrodynamic theory of integrable systems that incorporates the anomalous number of conserved quantities in those systems. The key idea of the theory rests upon the use of thermodynamic Bethe ansatz that allows us to express the essential ingredients in hydrodynamics, densities and currents average of conserved charges, in terms of the quasi-particle basis. In this talk I will review this new hydrodynamic theory, coined generalized hydrodynamics (GHD). I will first introduce the basics of GHD, highlighting the difference with the conventional hydrodynamics (i.e. hydrodynamics for non-integrable systems). I will then present some recent developments in the theory, such as the exact computation of the Drude weight and hydrodynamic correlation functions.

Venue: Building 14 #213, Yagami campus, Keio University

Event Official Language: English