iTHEMS Math Seminar
76 events

How many electrons can atoms bind?
May 13 (Wed) at 16:00  18:10, 2020
Dr. Yukimi Goto (Special Postdoctoral Researcher, iTHEMS)
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 manybody aspects of quantum mechanics and introduce some basic notions. The second part will deal with the mathematical results in some approximation theories.
Venue: via Zoom
Event Official Language: English

From Eigenvalues to Resonances
May 1 (Fri) at 16:00  18:10, 2020
Dr. Keita Mikami (Research Scientist, iTHEMS)
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.
Venue: via zoom
Event Official Language: English

Seminar
Index of the WilsonDirac operator revisited: a discrete version of Dirac operator on a finite lattice
February 25 (Tue) at 16:00  18:10, 2020
Dr. Mikio Furuta (Professor, The University of Tokyo)
The WilsonDirac 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/2graded Clifford module on a torus, it is known that (1) an integervalued index is defined for the WilsonDirac operator, and (2) the index is equal to the AtiyahSinger 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 WilsonDirac operator which can be immediately generalized to these various cases. Joint work with H. Fukaya, S. Matsuo, T. Onogi, S. Yamaguchi and M. Yamashita.
Venue: Seminar Room #160
Event Official Language: English

Solved and open problems regarding the neighborhood grid data structure
February 7 (Fri) at 16:00  18:10, 2020
Dr. Martin Skrodzki (Visiting Scientist, iTHEMS / Fellow, German Academic Scholarship Foundation, Germany)
February 7 at 16:0017:00 17:1018:10, 2020 In 2009, Joselli et al. introduced the neighborhood grid data structure for fast computation of neighborhood estimates for point clouds in arbitrary dimensions. Even though the data structure has been used in several applications and was shown to be practically relevant, it is theoretically not yet well understood even in the twodimensional case. The purpose of this talk is to present the data structure, give a timeoptimal building algorithm, and motivate several associated questions from enumerative combinatorics as well as lowdimensional (probabilistic) geometry. In case of questions that have been solved in the past, corresponding proofs will be provided. For the open question, the talk will list them as an outlook to possible future collaboration.
Venue: Seminar Room #160
Event Official Language: English

Seminar
Semiclassical methods in mathematical quantum mechanics
January 23 (Thu) at 16:00  18:10, 2020
Dr. Shu Nakamura (Professor, Gakushuin 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. 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 longrange perturbations. As an example of topics discussed in Talk 1, we discuss recent results on the scattering matrix with longrange 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.
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
Prof. 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
Noncommutative crepant resolutions and some higher dimensional flops
December 4 (Wed) at 16:00  18:10, 2019
Dr. 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
Some topics in projective geometry of algebraic varieties
November 8 (Fri) at 16:00  18:10, 2019
Dr. Atsushi Ito (Assistant Professor, 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

Seminar
AtiyahHirzebruch spectral sequence in the band theory
October 24 (Thu) at 16:00  18:10, 2019
Dr. 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
Dr. 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
Complex analysis on a neighborhood of a complex submanifold and its applications
July 30 (Tue) at 16:00  18:10, 2019
Dr. 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 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 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 semipositive curvature, and (ii) a study on nonprojective and nonKummer K3 surfaces.
Venue: Seminar Room #160
Event Official Language: English

Introduction to Schroedinger Operators
July 12 (Fri) at 16:00  18:10, 2019
Dr. 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 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: 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

Asymmetric metric and coarse geometry
June 20 (Thu) at 16:00  18:10, 2019
Dr. 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 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: 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

Certain invariants as dimension
May 24 (Fri) at 16:00  18:10, 2019
Dr. 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 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: 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
Dr. 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 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. 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 nonsmooth 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

Gauge Theory and Symmetries of 4Dimensional Spaces
April 26 (Fri) at 16:00  18:10, 2019
Dr. 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 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. 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 4dimensional spaces. As a recent development in this direction, I used gauge theory to study "the shape of the space of all symmetris of a 4dimensional 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 4dimensional 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
Dr. 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 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. 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
76 events
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