Seminar

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

ABBL/iTHEMS/r-EMU Joint Seminar: Towards systematic and consistent nuclear data inputs for astrophysical r-process with Bayesian approaches

June 28 (Fri) at 14:00 - 15:00, 2019

Haozhao Liang (Senior Research Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

This is his 2nd seminar talk for non-experts of nuclear physics, following the 1st one on 18th Jan. 2019. Abstract: In this interdisciplinary talk, I will start with some basic concepts as well as some frontiers of nuclear physics, and then introduce the roles of nuclear data inputs for the study of astrophysical rapid neutron-capture process (r-process), which is responsible for the creation of approximately half the abundances of the atomic nuclei heavier than iron. Recent progress in nuclear physics focuses on improving the accuracy of crucial nuclear inputs, such as nuclear masses, beta-decay half-lives. Nevertheless, in most of the studies these inputs are investigated individually. One of our ongoing attempts is to organize the crucial nuclear inputs in a systematic and consistent way, together with Bayesian and/or machine learning approaches, which are able to provide not only the theoretical results but also the corresponding uncertainties.

Venue: 224-226, Main Research Building

Event Official Language: English

Asymmetric metric and coarse geometry

June 20 (Thu) at 16:00 - 18:10, 2019

Hiroki Kodama (Visiting Scientist, iTHEMS / Assistant Professor, Advanced Institute for Materials Research (AIMR), Tohoku 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: For most of mathematicians, metric is symmetric. However, we can define asymmetric metric without any difficulty. "Coarse" is a notion to describe some large scale viewpoint. For example, the set of real numbers is coarse equivalent to the set of integers (with respect to standard metric). I will discuss asymmetric metric space in "coarse" sense. Part 1: I will define metric space and asymmetric metric space. I will also explain a notion of coarse equivalence. Part 2: I will discuss what kind of asymmetric metric space is not coarse equivalent to (symmetric) metric space. I also would like to give other generalizations of metric.

Venue: Seminar Room #160

Event Official Language: English

Using combined Particles-in-MHD-Cells to model particle acceleration in astrophysical shocks

June 17 (Mon) at 14:00 - 15:00, 2019

Allard Jan van Marle (Research Professor, Ulsan National Institute of Science and Technology, Republic of Korea)

Astrophysical shocks can accelerate charged particles through diffusive shock acceleration. This process involves repeated shock crossings where the particle gains energy from collisions with the electromagnetic field. Eventually, these particles will reach relativistic speeds and can be observed as cosmic rays. In order to simulate this process, we need a method that can handle both the large-scale structure of astrophysical shocks, as well as the behaviour of individual particles. We achieve this by combining the classical magnetohydrodynamics (MHD) and particle-in-cell (PIC) methods. This allows us to describe the thermal plasma of the shock through MHD, while simultaneously using PIC to follow the movement of non-thermal particles as they are accelerated. Our results show a complicated interaction that destabilizes the shock, reducing the efficiency with which particles can be accelerated.

Venue: Seminar Room #132

Event Official Language: English

Quantum physics and science with open-source software: QuTiP, the Quantum Toolbox in Python

June 13 (Thu) at 10:00 - 11:30, 2019

Nathan Shammah (Postdoctoral Researcher, Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research (CPR))

I will address the rise of open source software based on the Python language ecosystem in quantum physics research, in particular with relevance to quantum technology and quantum computing. I will introduce the Quantum Toolbox in Python, QuTiP, a very popular software in the quantum tech community, whose core development has revolved around Prof. F. Nori’s group at RIKEN since 2011. QuTiP is open-source software for simulating the dynamics of closed and open quantum systems, and is used for quantum information science and cavity quantum electrodynamics studies. The QuTiP ecosystem has grown considerably in the past years, with many quantum tech libraries using its functionalities, similarly to what has happened for AstroPy in the astrophysics community. Following the seminar, an interactive session will illustrate some features of this software package library. I will also show, drawing from recent research examples, how everyone can build its own library. Only a laptop with wifi working is required to join the hands-on session.

Venue: Nishina Hall

Event Official Language: English

Quantum Mechanics of an Evaporating Black Hole

June 6 (Thu) at 15:30 - 17:00, 2019

Yasunori Nomura (Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)

Venue: Seminar Room #160

Event Official Language: English

ABBL-iTHEMS Joint Seminars (Following r-EMU seminar 13:30-15:00)

May 31 (Fri) at 15:15 - 17:35, 2019

15:15-15:35 Hiroyuki Sagawa (ICRR, U.Tokyo) “Recent TA Results and the extension status for the study of the highest-energy cosmic rays” 15:35-16:30 Igor Tkachev (Russian Academy of Sciences) “Axion stars: from birth to death” 16:30-16:40 Break 16:40-17:35 Peter Tinyakov (U. Libre de Bruxelles) “Solar mass black holes and dark matter"

Venue: #435-437, Main Research Building

Event Official Language: English

Certain invariants as dimension

May 24 (Fri) at 16:00 - 18:10, 2019

Genki Ouchi (Special Postdoctoral Researcher, 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 talk, I would like to talk about certain invariants that look like dimension. This talk has independent two parts. In part 1, I will talk about finite metric spaces. In 2013, Leinster introduced the notion of magnitude of finite metric spaces. It measures effective number of points in finite metric spaces. Considering magnitude and scale transformation, Leinster and Willerton defined dimension of finite metric space with scale. I will explain the definition of magnitude of finite metric spaces and see examples. In part 2, I will talk about derived categories of smooth projective varieties or finite dimensional algebras. In 2014, Dimitrov, Heiden, Katzarkov and Kontsevich introduced the notion of entropy of endofunctors of derived categories. It measures complexity of endofunctors under iteration. Serre functor is an autoequivalence of derived category, that describes Serre duality. Entropy of Serre functor looks like dimension of derived categories. I will talk about known results for entropy of Serre functors and some related topics.

Venue: Seminar Room #160

Event Official Language: English

Introduction to Singularity Theory in Algebraic Geometry

May 16 (Thu) at 16:00 - 18:10, 2019

Kenta Sato (Special Postdoctoral Researcher, 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. In this talk, I will explain for all scientists how singularities are studied in algebraic geometry. In algebraic geometry, we study algebraic varieties, which are figures defined as the zero sets of polynomial equations. To study an algebraic variety, we often expect that the variety is smooth, that is, the variety locally resembles Euclidian spaces. However, even if we start from smooth varieties, we sometimes encounter non-smooth varieties. This is one of the reasons why we need to study singularities. Part I: In the first one hour, I will explain how singularities are studied. I will introduce two invariants of singularities by which we can compare singularities numerically. One invariant is defined in terms of resolution of singularities and the other is defined in terms of positive characteristic methods. I also explain a surprising relation of these invariants. Part II: In the second one hour, I will explain how singularity theory is used to study smooth projective varieties. I will introduce Minimal Model Program and explain the relation with singularity theory.

Venue: Seminar Room #160

Event Official Language: English

Three quantizations of conformal field theory

May 1 (Wed) at 15:40 - 17:30, 2019

Tsukasa Tada (Coordinator, iTHEMS / Vice Chief Scientist, Quantum Hadron Physics Laboratory, RIKEN Nishina Center for Accelerator-Based Science (RNC))

Needless to say, conformal field theory is elemental in the study of string theory, statistical quantum systems, and various quantum field theories. Two-dimensional conformal field theory is usually quantized by the so-called radial quantization. However, this is not the only way. As a matter of fact, there are two other distinctive choices for the time foliation, or equivalently, the Hamiltonian. One of these choices yields the continuous Virasoro algebra, while the other choice leads to the Virasoro algebra on a torus. The former case corresponds to the recently found (and perhaps less known) phenomenon, sine-square deformation. The latter yields the well-known entanglement entropy. I will present a comprehensive treatment of these three quantizations and discuss its physical implications.

Venue: Old LeConte Hall 402, UC Berkeley

Event Official Language: English

Gauge Theory and Symmetries of 4-Dimensional Spaces

April 26 (Fri) at 16:00 - 18:10, 2019

Hokuto Konno (Special Postdoctoral Researcher, 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. Although the term "gauge theory" is usually used in physical contexts, in the early 1980's, mathematicians found that gauge theory has many striking applications to purely mathematical problems. Most of typical applications are related to topology of 4-dimensional spaces. As a recent development in this direction, I used gauge theory to study "the shape of the space of all symmetris of a 4-dimensional space". In the first one hour, I will explain a notion of mathematical spaces, called manifolds, and try to describe the idea: how mathematicians make use of gauge theory to study the topology of a 4-dimensional manifold. In the second one hour, I will explain what the space of symmetries of a manifold means, and which type of theorems about the space of symmetries can be obtained using gauge theory.

Venue: Seminar Room #160

Event Official Language: English

Introduction to Galois Theory and Class Field Theory

April 18 (Thu) at 16:00 - 18:00, 2019

Hiroyasu Miyazaki (Special Postdoctoral Researcher, 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. Part I: Galois theory is one of the most important theories in mathematics. Speaking in one phrase, it explains the correspondence between “extensions of numbers” and “subgroups of Galois group”. Basically, finding subgroups of a finite group is much easier than finding extensions of numbers. As a result, Galois theory has incredibly strong applications. For example, we can prove polynomial equations of degree greater than 4 are not always solvable by radicals, which is a celebrated result by Abel and Galois. In the first part of the talk, I will introduce Galois theory in an accessible way for all scientists. Part II: Class Field Theory (CFT) is a monumental work in number theory. Given Galois theory, which is explained in Part I, classifying “extension of numbers” is reduced to classifying “subgroups of Galois group”. So, the next thing to do would be to analyze the structure of Galois groups. CFT enables us to describe the Galois group of a number field K by using only the language of K, i.e., not by using its extensions. In the second part of the talk, I will explain CFT in an as accessible way as possible for all scientists (in particular, also for mathematicians). If time permits, I would like to explain a geometric interpretation of Galois theory, and higher dimensional CFT.

Venue: Seminar Room #160

Event Official Language: English

ABBL, iTHEMS, r-EMU Joint Seminar: Impacts of New Carbon Fusion Cross Sections on Type Ia Supernovae

April 12 (Fri) at 15:00 - 16:00, 2019

Kanji Mori

Venue: Seminar Room #132

Event Official Language: English

iTHEMS Seminar+discussion on "non-equilibrium physics of living matter"

April 8 (Mon) at 14:00 - 15:30, 2019

Kyogo Kawaguchi (The University of Tokyo / RIKEN Hakubi Team Leader, Nonequilibrium physics of living matter RIKEN Hakubi Research Team, RIKEN Center for Biosystems Dynamics Research (BDR))
Kyosuke Adachi (Research Scientist, Nonequilibrium Physics of Living Matter RIKEN Hakubi Research Team, RIKEN Center for Biosystems Dynamics Research (BDR))

14:00-14:50 (40 min. talk + 10 min discussion) "Physical" problems in multicellular dynamics and cell differentiation Kyogo Kawaguchi (RIKEN Hakubi Research Group) 14:50-15:30 (30 min. talk + 10 min. discussion) Phase transition in a chromatin model with epigenetic modification Kyosuke Adachi (Kawaguchi Lab.) 15:30- Informal discussions

Venue: Seminar Room #160

Event Official Language: English

Lifting low dimensional local systems

April 3 (Wed) at 15:45 - 16:45, 2019

De Clercq Charles (Université Paris 13, Sorbonne, France)

The content of this seminar is basically for mathematicians (sorry). If you are interested in how a professional math seminar works, please feel free to join! A long-standing conjecture predicts the existence of lifts for Galois representations with F_p coefficients to p-adic coefficients. The case 2-dimensional representations of the absolute Galois group of Q is closely related to Serre's modularity conjecture, proved by Khare and Witenberger. After some recollection on the state of the art about this problem, i will develop the machinery underneath the notion of smooth profinite groups. We will then show how this machinery allows to prove some lifting theorems for low dimensional Galois representations and local systems, getting out of the classical arithmetic world usually considered for this conjecture.

Venue: Seminar Room #160

Event Official Language: English

The Origin of the X-ray Clumpy Ejecta in Type Ia Supernova Remnants

April 3 (Wed) at 14:00 - 15:00, 2019

Toshiki Sato (Special Postdoctoral Researcher, High Energy Astrophysics Laboratory, RIKEN Cluster for Pioneering Research (CPR))

X-ray-emitting clumpy structures are generally observed in young Type Ia supernova remnants although the origin is still obscure. There are two candidates for explaining the formation of clumps; initial clumpiness in ejecta at the explosion (i.e., clumpy ejecta model) or hydrodynamic instabilities made from smooth ejecta profile (i.e., smooth ejecta model). This information should reflect the initial ejecta structure of SNe Ia, so it is important for understanding the Type Ia explosion itself. Our preliminary investigations into constraining the structure of SN Ia remnants using Fourier and wavelet-transform analyses did not turn out to be sufficiently powerful at discriminating the two hydro models and the observed Tycho image from each other. This led us to investigate an approach that would be more sensitive to patterns in the distribution of clumps and holes in the images, such as the "genus statistic.” In this study, for the first time, the genus statistics have been applied to a famous type Ia remnant, Tycho (SN 1572) to understand the formation of the clumps by comparing with hydrodynamical models (Sato et al. 2019, arXiv: 1903.00764). We found the genus curve from Tycho's supernova remnant strongly indicates a skewed non-Gaussian distribution of the ejecta clumps, which is similar to that of a hydrodynamical model for the clumpy ejecta model. In contrast, a hydrodynamical model for the smooth ejecta model has a genus curve that is similar to that of a random Gaussian distribution. Thus, our results support the initial clumpiness in the Type Ia ejecta is more reasonable for the origin of the clumps and demonstrate usefulness of the genus statistics for this field. In addition, we will also discuss the origin of “Fe-rich” ejecta clumps in Type Ia SNRs in this seminar.

Venue: #433, Main Research Building

Event Official Language: English

Tensor Berry connections and their topological invariants

April 2 (Tue) at 14:00 - 15:00, 2019

Giandomenico Palumbo (Researcher, Université Libre de Bruxelles, Belgium)

The Berry connection plays a central role in our description of the geometric phase and topological phenomena. In condensed matter, it describes the parallel transport of Bloch states and acts as an effective "electromagnetic" vector potential defined in momentum space. Inspired by developments in high-energy physics, where higher-form Kalb-Ramond gauge fields were introduced, I hereby explore the existence of "tensor Berry connections" in quantum matter. My approach consists in a general construction of effective gauge fields, which I ultimately relate to the components of Bloch states. I apply this formalism to various models of topological matter, and I investigate the topological invariants that result from generalized Berry connections. I introduce the 2D Zak phase of a tensor Berry connection, which I then relate to the more conventional first Chern number; I also reinterpret the winding number characterizing 3D topological insulators to a Dixmier-Douady invariant, which is associated with the curvature of a tensor connection. Besides, my approach identifies the Berry connection of tensor monopoles, which are found in 4D Weyl-type systems in ultracold atoms.

Venue: Seminar Room #160

Event Official Language: English