iTHEMS数学セミナー

セミナー

Recent progress on dualities in W-superalgebras

2022年1月28日16:00 - 18:00

Vertex superalgebras are algebras which describe the chiral part of two dimensional superconformal field theory. A rich and fundamental class is provided by the affine vertex superalgebras associated with simple Lie superalgebras and the W-superalgebras obtained from them by cohomology parametrized by nilpotent orbits. Historically, the W-algebras associated with simple Lie algebras and principal nilpotent orbit have been studied intensively and are well-known to play an essential role in the quantum geometric Langlands program. In particular, they enjoy a duality, called the Feigin-Frenkel duality, which is a chiral analogue of the isomorphism between centers of the enveloping algebras of simple Lie algebras in Langlands duality. Recently, physicists found a suitable generalization for other types of nilpotent orbits from study on four dimensional supersymmetric gauge theory. In this talk, I will report the recent progress on our understanding of dualities in W-superalgebras since then in terms of several aspects: algebras, modules, and fusion rules.

イベント公式言語: 英語

セミナー

The Ohsawa-Takegoshi $L^2$ extension theorem and variations of Bergman kernels

2022年1月14日16:00 - 18:00

In complex analysis and geometry, $L^2$ methods are very important and widely used. Recent studies show that the $L^2$ theory and the variational theory are closely related. In particular, the (optimal) $L^2$ extension theorem can be proved by subharmonicity of variations of Bergman kernels and vice versa. In this talk, I will explain the background, results, and key ideas of the proof. *Please contact Keita Mikami mailing address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Generalized Bernoulli process and computation of proportional areas for Venn diagram

2021年12月8日16:00 - 18:00

イベント公式言語: 英語

セミナー

The Conley index of topological dynamical systems

2021年12月3日16:00 - 18:00

The study of topological dynamical systems, i.e. continuous self-homeomorphisms (or continuous flows) on topological spaces, is important in both pure mathematics and applications. To each isolated invariant subset of a topological dynamical system, we can assign an invariant called the Conley index, which is (roughly speaking) a based space that describes the dynamics around the isolated invariant subset. It is used not only in the study of topological dynamical systems themselves but also in Manolescu’s construction of the Seiberg-Witten-Floer homotopy type (a spectrum-valued (3+1)-dimensional TQFT). In this talk, I am planning to explain a new construction of Conley indices, which is entirely non-homotopical and uses only basic general topology. *Please contact Keita Mikami or Hiroyasu Miyazaki's mailing address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

2021年11月26日16:00 - 18:00

イベント公式言語: 英語

セミナー

The graph removal lemma

2021年11月19日16:00 - 18:00

We have recently proved an extension of the Green-Tao theorem on arithmetic progressions to number fields, in collaboration with Kai, Mimura, Munemasa and Yoshino. (Kai gave a talk on this result in March.) There are several promising approaches in this area, including ergodic theory and Fourier analysis, but we used a combinatorial tool, the relative hypergraph removal lemma proved by Conlon, Fox and Zhao. In the first half of this talk, I will give a survey of Szemerédi's regularity lemma and the graph removal lemma, and explain how to extend the removal lemma to the case of (weighted) hypergraphs. In the second half of this talk, I will present Fox's result on a quantitative version of the graph removal, and discuss the prospects for future research. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Confluence for the K-theoretic J-function

2021年11月12日16:00 - 18:00

Prof. Todor Milanov (東京大学 カブリ数物連携宇宙研究機構 (Kavli IPMU) 准教授)

I am planning to talk about my recent paper (1) written in collaboration with Alexis Roquefeuil. In the first part of the talk I would like to explain the background of our project: quantum differential equations and K-theoretic quantum q-difference equations in genus-0 Gromov--Witten theory. In the second part of the talk, I would like to explain our main result with an interesting application. Namely, under the assumption that the first Chern class of the tangent bundle is positive, we proved that the small J-function in quantum cohomology can be obtained as a limit q -->1 of the small J-function in quantum K-theory. In the case of a Fano toric manifold of Picard rank 2, we proved the K-theoretic version of an identity due to Iritani that relates the I-function of the toric manifold and the oscillatory integral of the toric mirror. In particular, our confluence result yields a new proof of Iritani's identity in the case of a Fano toric manifold of Picard rank 2. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Geometry and Physics of Mirror Symmetry

2021年11月5日16:00 - 18:00

Prof. Naichung Conan Leung (Professor of Mathematics, Department of Mathematics, The Institute of Mathematical Sciences, The Chinese University of Hong Kong, Hong Kong)

In the first half of this talk, I will describe the geometry and physics behind mirror symmetry in layman's terms. In the second half of this talk, I will provide a more mathematical explanation of the concepts involved in this mysterious conjecture. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Geometry of hyperkahler 4 manifolds

2021年10月22日13:00 - 15:00

Prof. Song Sun (Associate Professor, Department of Mathematics, University of California, Berkeley, USA)

An n dimensional Riemannian metric g defines a holonomy group, which is a subgroup of SO(n) given by parallel transport along all contractible loops (with respect to the Levi-Civita connection). According to the Berger classification we know that if a complete Riemannian metric is not locally symmetric and not locally reducible then its holonomy group is either the entire SO(n) (generic case), or U(n) (Kahler), or is special and belongs to a small list. Riemannian metrics with special holonomy are very interesting geometric objects to study, with many connections to analysis and physics. The simplest model is given by a 4 dimensional hyperkahler metric. We will explain the general background and discuss recent progress on understanding the geometry of hyperkahler 4 manifolds. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

The branched deformations of special Lagrangian submanifolds

2021年10月15日10:00 - 12:00

Prof. Siqi He (Research Assistant Professor, Simons Center for Geometry and Physics, Stony Brook University, USA)

Special Lagrangian submanifolds are a distinguished class of real calibrated submanifolds defined in a Calabi-Yau manifold, which are calibrated by the real part of the holomorphic volume form. Given a compact, smooth special Lagrangian submanifold, Mclean proved that the space of nearby special Lagrangian submanifolds of it could be parametrized by the harmonic 1-forms. In this talk, we will discuss some recent progress on generalizing Mclean’s result to the branched deformations. We will describe how to use multi-valued harmonic functions to construct branched nearby deformations. In the first one hour, we will introduce the background of special Lagrangian submanifold and explain the motivations to study this problem. In this second one hour, we will discuss the technical details and interesting new phenomenon in this branching deformation problem. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Geography of varieties of general type

2021年10月8日16:00 - 18:10

Prof. Chen Jiang (Associate Professor, Shanghai Math Center, Fudan University, China)

We study birational invariants in order to study birational classifications of varieties. Geography is the study of relations among different invariants. We will focus on two fundamental invariants: canonical volume and geometric genus. For surfaces there are classical results such as Miyaoka-Yau inequality and Noether inequality. I will discuss higher dimensional analogue of them, and introduce our recent work on the optimal Noehter inequality for 3-folds joint with Jungkai Chen and Meng Chen. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

Donaldson-Thomas invariants, wall-crossing and categorifications

2021年10月1日16:00 - 18:10

It is an important subject to study algebraic curves inside algebraic varieties, both in classical algebraic geometry and also enumerative geometry inspired by string theory. The Donaldson-Thomas theory is one of curve counting theories on Calabi-Yau 3-folds, and has developed in these 20 years from several aspects of mathematics and mathematical physics. Among them, the wall-crossing in derived category turned out to be a key phenomena in proving deep structures of generating series of Donaldson-Thomas invariants. In the first one hour, I will review the classical aspect of counting curves inside algebraic varieties, and explain how it leads to modern enumerative geometry such as Gromov-Witten invariants, Donaldson-Thomas invariants. In the second one hour, I will explain wall-crossing phenomena in Donaldson-Thomas theory, and its categorification in the case of the resolved conifold. *Please contact Keita Mikami's mail address to get access to the Zoom meeting room.

イベント公式言語: 英語

セミナー

From Yang-Mills theory to enumerative geometry on Calabi-Yau 4-folds

2021年8月6日16:00 - 18:10

ヤーロン・ツァオ (数理創造プログラム 研究員)

Yang-Mills theory was studied from mathematical perspectives in the 1970s by Atiyah and his collaborators (notably Drinfeld, Hitchin, Singer). Subsequent breakthroughs were made on dimensions 3 and 4 by Floer and Donaldson (based on deep analytic results obtained by Uhlenbeck and Taubes) in the 1980s. In 1996, Donaldson and Thomas proposed to study Yang-Mills theories on dimensions bigger than 4. In higher dimensions, the analytic method is limited and algebro-geometric method is heavily used instead. This powerful tool usually enables us to compute partition functions and lead to amazing links to other invariants in enumerative geometry, e.g. Gromov-Witten and Gopakumar-Vafa invariants. In this talk, I will review some of these inspiring stories and discuss how my works on Calabi-Yau 4-folds fit into them.

イベント公式言語: 英語

セミナー

An introduction to modular functions, conformal field theories, and moonshine phenomena

2021年7月2日16:00 - 18:10

Moonshine phenomena are certain mysterious connections between modular functions and finite groups. The first example is the celebrated monstrous moonshine, which connects the J-invariant and the Monster group. Surprisingly, this relationship can be well understood in terms of chiral conformal field theory. In this talk, I would like to explain what is chiral conformal field theory and how it gives moonshine phenomena. In the first part of the talk, the notion of modular function will be introduced and the precise statement of the monstrous moonshine will be given. Then the monstrous moonshine will be explained in terms of vertex operator algebra, a mathematical model of chiral conformal field theory. In the second part of the talk, we focus on the question: what is chiral conformal field theory mathematically? In addition to vertex operator algebras, other mathematical models of chiral conformal field theory, namely conformal nets and Segal conformal field theories, will be introduced. Recent progress on the relationship among these three models, including the Carpi--Kawahigashi--Longo--Weiner correspondence and the geometric realization of conformal nets will also be reviewed.

イベント公式言語: 英語

セミナー

Stable eigenvalues of compact anti-de Sitter 3-manifolds

2021年6月18日16:00 - 18:10

Geometric objects that have been investigated in detail so far, such as closed Riemann surfaces, are sometimes locally homogeneous. Loosely speaking, their infinitesimal behavior is the same at each point. In this talk, I would like to explain the idea of investigating such objects using the Lie group theory.In the first part of the talk, I will recall the notions of Lie group actions and their quotient spaces with examples, and then explain the definitions of locally homogeneous spaces and their deformations (Teichmüller spaces). In the second part of the talk, I will consider anti-de Sitter manifolds as a special case, i.e., Lorentzian manifolds of negative constant curvature. As in the Riemannian case, a differential operator called the Laplacian (or the Klein-Gordon operator) is defined on Lorentzian manifolds. Unlike the Riemannian case, it is no longer an elliptic differential operator but a hyperbolic differential operator. In its spectral analysis, new phenomena different from those in the Riemannian case have been discovered in recent years, following pioneering works by Toshiyuki Kobayashi and Fanny Kassel. I would like to explain stable eigenvalues of the hyperbolic Laplacian of anti-de Sitter 3-manifolds with recent progress.

イベント公式言語: 英語

セミナー

Loewner's theorem for maps on operator domains / The structure of maps on the space of all quantum pure states that preserve a fixed quantum angle

2021年5月24日16:00 - 18:10

This talk is divided into two independent topics. In the first part of my talk we consider the order structure of hermitian matrices. Given two matrix domains (open connected sets of n-by-n hermitian matrices), what is the general form of order isomorphisms between them? I will explain that there is a complete correspondence between the class of order isomorphisms and that of biholomorphic mappings. In the second part we consider the metric structure of the space P(H) of all quantum pure states (= the projective space of a complex Hilbert space H). Wigner's theorem asserts that every surjective isometry of P(H) onto itself is implemented by a unitary or an antiunitary operator. Uhlhorn generalized Wigner's theorem by showing that every bijective transformation of P(H) that preserves orthogonality is implemented by a unitary or an antiunitary operator. We consider some variants of Uhlhorn's result. The first part is joint work with P. Semrl (Univ. of Ljubljana), and the second part with G.P. Geher (Univ. of Reading). Only basic linear algebra is assumed in both parts.

イベント公式言語: 英語

セミナー

Geometry of canonical metrics on Kähler manifolds

2021年5月14日16:00 - 18:10

The aim of this talk is to report recent trends in Kähler geometry. Kähler geometry consists of two aspects: the one is algebraic geometry and the other is metric geometry.The first one hour is an introduction for non-mathematicians. I begin with a simple example of algebraic variety from ancient Greek, which I believe is the simplest example illustrating motivation for compact complex manifolds. On the other hand, I explain the first motivation for canonical metrics in Kähler geometry via Riemann’s uniformization theorem.The last one hour is an introduction to recent trends in Kähler geometry, especially Kähler-Einstein metrics. The existence of Kähler-Einstein metrics turns out to be related to geometry of degenerations of space, which is so called Yau-Tian-Donaldson conjecture. I explain various aspects of this topic. We encounter deep studies in metric geometry, birational geometry and non-archimedean geometry. I finally explain recent breakthrough on Kähler-Ricci flow.The goal of this talk is the starting point of my study. I briefly explain my study if time permits.

イベント公式言語: 英語

セミナー

Alternative tsunami observing and forecasting systems

2021年4月22日16:00 - 18:10

イヤン・ムリア (理化学研究所 開拓研究本部 (CPR) 三好予測科学研究室 研究員)

Dedicated tsunami observing systems are mostly expensive and are often not sustainable. Therefore, alternative approaches should be implemented to overcome the issues. We introduced innovative ways to observe tsunamis using existing instrumentation available on unconventional platforms such as commercial vessels and airplanes. Our study demonstrated that the accuracy of the proposed observing systems is adequate for detecting large tsunamis offshore. The use of such systems is expected to provide more cost-effective and sustainable observations for the future. Additionally, we also developed a tsunami forecasting system based on machine learning to improve or complement the conventional methods that typically require considerable computational resources. On the contrary, the main appealing feature of the machine learning is the computational speed that would be suitable for a real-time prediction of tsunami inundation or flooding. We found that the application of machine learning can significantly improve the computing time without sacrificing the accuracy compared to the conventional methods.

イベント公式言語: 英語

セミナー

Long-time behavior of moving solids in a fluid and the kinetic theory of gases

2021年4月7日16:00 - 18:10

Understanding dynamics of solids in a fluid is a fundamental problem in fluid dynamics. Due to the growing interest in engineering in out-of-equilibrium situations, moving boundary problems for kinetic equations such as the Boltzmann equation have become an active area of research. In the first part of the talk, I shall explain recent, especially mathematical, developments in this field. Then in the second part, I'd like to explain my results concerning the long-time behavior of a point particle moving in a 1D viscous compressible fluid. These results aim to give some explanation of related numerical simulations for a BGK model of the Boltzmann equation.

イベント公式言語: 英語

セミナー

The Green-Tao theorem for number fields

2021年3月22日16:00 - 18:10

5, 11, 17, 23, 29 are prime numbers which form an arithmetic progression of length 5. A famous theorem of Ben Green and Terence Tao in 2008 says there are arbitrarily long arithmetic progressions of prime numbers. Algebraic number theorists are also interested in more general numbers like square roots of integers. Recently, Mimura, Munemasa, Seki, Yoshino and I have established a generalization of the Green-Tao theorem in such a direction. In the first 50 minutes of my talk, I would like to explain some background and technology behind the Green-Tao theorem. In the second half after a break, I explain the concept of number fields to formulate our generalization of their result. I will also discuss how one of the new difficulties, which I call the norm vs length conflict, is handled by a technique called Geometry of Numbers. *Please contact Keita Mikami or Hiroyasu Miyazaki's mailing address to get access to the Zoom meeting room.

イベント公式言語: 英語