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2018年11月12日(月)
東京確率論セミナー
16:00-17:30 数理科学研究科棟(駒場) 128号室
Alejandro Ramirez 氏 (Pontificia Universidad Catolica de Chile)
Random walk at weak and strong disorder (ENGLISH)
http://www.mat.uc.cl/~aramirez/
Alejandro Ramirez 氏 (Pontificia Universidad Catolica de Chile)
Random walk at weak and strong disorder (ENGLISH)
[ 講演概要 ]
We consider random walks at low disorder on $\mathbb Z^d$. For dimensions $d\ge 4$, we exhibit a phase transition on the strength of the disorder expressed as an equality between the quenched and annealed rate functions. In dimension $d=2$ we exhibit a universal scaling limit to the stochastic heat equation. This talk is based on joint works with Bazaes, Mukherjee and Saglietti, and with Moreno and Quastel.
[ 参考URL ]We consider random walks at low disorder on $\mathbb Z^d$. For dimensions $d\ge 4$, we exhibit a phase transition on the strength of the disorder expressed as an equality between the quenched and annealed rate functions. In dimension $d=2$ we exhibit a universal scaling limit to the stochastic heat equation. This talk is based on joint works with Bazaes, Mukherjee and Saglietti, and with Moreno and Quastel.
http://www.mat.uc.cl/~aramirez/
2018年11月09日(金)
統計数学セミナー
11:00-12:00 数理科学研究科棟(駒場) 123号室
Frédéric Abergel 氏 (CentraleSupélec)
Market impact and option hedging in the presence of liquidity costs
Frédéric Abergel 氏 (CentraleSupélec)
Market impact and option hedging in the presence of liquidity costs
[ 講演概要 ]
The phenomenon of market (or: price) impact is well-known among practicioners, and it has long been recognized as a key feature of trading in electronic markets. In the first part of this talk, I will present some new, recent results on market impact, especially for limit orders. I will then propose a theory for option hedging in the presence of liquidity costs.(Based on joint works with E. Saïd, G. Loeper).
The phenomenon of market (or: price) impact is well-known among practicioners, and it has long been recognized as a key feature of trading in electronic markets. In the first part of this talk, I will present some new, recent results on market impact, especially for limit orders. I will then propose a theory for option hedging in the presence of liquidity costs.(Based on joint works with E. Saïd, G. Loeper).
2018年11月08日(木)
トポロジー火曜セミナー
10:30-12:00 数理科学研究科棟(駒場) 056号室
開催日，時刻にご注意下さい
Michael Heusener 氏 (Université Clermont Auvergne)
Deformations of diagonal representations of knot groups into $\mathrm{SL}(n,\mathbb{C})$ (ENGLISH)
開催日，時刻にご注意下さい
Michael Heusener 氏 (Université Clermont Auvergne)
Deformations of diagonal representations of knot groups into $\mathrm{SL}(n,\mathbb{C})$ (ENGLISH)
[ 講演概要 ]
This is joint work with Leila Ben Abdelghani, Monastir (Tunisia).
Given a manifold $M$, the variety of representations of $\pi_1(M)$ into $\mathrm{SL}(2,\mathbb{C})$ and the variety of characters of such representations both contain information of the topology of $M$. Since the foundational work of W.P. Thurston and Culler & Shalen, the varieties of $\mathrm{SL}(2,\mathbb{C})$-characters have been extensively studied. This is specially interesting for $3$-dimensional manifolds, where the fundamental group and the geometrical properties of the manifold are strongly related.
However, much less is known of the character varieties for other groups, notably for $\mathrm{SL}(n,\mathbb{C})$ with $n\geq 3$. The $\mathrm{SL}(n,\mathbb{C})$-character varieties for free groups have been studied by S. Lawton and P. Will, and the $\mathrm{SL}(3,\mathbb{C})$-character variety of torus knot groups has been determined by V. Munoz and J. Porti.
In this talk I will present some results concerning the deformations of diagonal representations of knot groups in basic notations and some recent results concerning the representation and character varieties of $3$-manifold groups and in particular knot groups. In particular, we are interested in the local structure of the $\mathrm{SL}(n,\mathbb{C})$-representation variety at the diagonal representation.
This is joint work with Leila Ben Abdelghani, Monastir (Tunisia).
Given a manifold $M$, the variety of representations of $\pi_1(M)$ into $\mathrm{SL}(2,\mathbb{C})$ and the variety of characters of such representations both contain information of the topology of $M$. Since the foundational work of W.P. Thurston and Culler & Shalen, the varieties of $\mathrm{SL}(2,\mathbb{C})$-characters have been extensively studied. This is specially interesting for $3$-dimensional manifolds, where the fundamental group and the geometrical properties of the manifold are strongly related.
However, much less is known of the character varieties for other groups, notably for $\mathrm{SL}(n,\mathbb{C})$ with $n\geq 3$. The $\mathrm{SL}(n,\mathbb{C})$-character varieties for free groups have been studied by S. Lawton and P. Will, and the $\mathrm{SL}(3,\mathbb{C})$-character variety of torus knot groups has been determined by V. Munoz and J. Porti.
In this talk I will present some results concerning the deformations of diagonal representations of knot groups in basic notations and some recent results concerning the representation and character varieties of $3$-manifold groups and in particular knot groups. In particular, we are interested in the local structure of the $\mathrm{SL}(n,\mathbb{C})$-representation variety at the diagonal representation.
2018年11月06日(火)
解析学火曜セミナー
16:50-18:20 数理科学研究科棟(駒場) 128号室
柴田徹太郎 氏 (広島大学)
Global behavior of bifurcation curves and related topics (日本語)
柴田徹太郎 氏 (広島大学)
Global behavior of bifurcation curves and related topics (日本語)
[ 講演概要 ]
In this talk, we consider the asymptotic behavior of bifurcation curves for ODE with oscillatory nonlinear term. First, we study the global and local behavior of oscillatory bifurcation curves. We also consider the bifurcation problems with nonlinear diffusion.
In this talk, we consider the asymptotic behavior of bifurcation curves for ODE with oscillatory nonlinear term. First, we study the global and local behavior of oscillatory bifurcation curves. We also consider the bifurcation problems with nonlinear diffusion.
トポロジー火曜セミナー
17:30-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 17:00-17:30
尾國 新一 氏 (愛媛大学)
Coarsely convex spaces and a coarse Cartan-Hadamard theorem (JAPANESE)
Tea: Common Room 17:00-17:30
尾國 新一 氏 (愛媛大学)
Coarsely convex spaces and a coarse Cartan-Hadamard theorem (JAPANESE)
[ 講演概要 ]
A coarse version of negatively-curved spaces have been very well studied as Gromov hyperbolic spaces. Recently we introduced a coarse version of non-positively curved spaces, named them coarsely convex spaces and showed a coarse version of the Cartan-Hadamard theorem for such spaces in a joint-work with Tomohiro Fukaya (arXiv:1705.05588). Based on the work, I introduce coarsely convex spaces and explain a coarse Cartan-Hadamard theorem, ideas for proof and its applications to differential topology.
A coarse version of negatively-curved spaces have been very well studied as Gromov hyperbolic spaces. Recently we introduced a coarse version of non-positively curved spaces, named them coarsely convex spaces and showed a coarse version of the Cartan-Hadamard theorem for such spaces in a joint-work with Tomohiro Fukaya (arXiv:1705.05588). Based on the work, I introduce coarsely convex spaces and explain a coarse Cartan-Hadamard theorem, ideas for proof and its applications to differential topology.
2018年11月05日(月)
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
志賀啓成 氏 (東京工業大学)
On the quasiconformal equivalence of Dynamical Cantor sets (JAPANESE)
志賀啓成 氏 (東京工業大学)
On the quasiconformal equivalence of Dynamical Cantor sets (JAPANESE)
[ 講演概要 ]
Let $E$ be a Cantor set in the Riemann sphere $\widehat{\mathbb C}$, that is, a totally disconnected perfect set in $\widehat{\mathbb C}$.
The standard middle one-thirds Cantor set $\mathcal{C}$ is a typical example.
We consider the complement $X_{E}:=\widehat{\mathbb C}\setminus E$ of the Cantor set $E$.
It is an open Riemann surface with uncountable many boundary components.
We are interested in the quasiconformal equivalence of such surfaces.
In this talk, we discuss the quasiconformal equivalence for the complements of Cantor sets given by dynamical systems.
Let $E$ be a Cantor set in the Riemann sphere $\widehat{\mathbb C}$, that is, a totally disconnected perfect set in $\widehat{\mathbb C}$.
The standard middle one-thirds Cantor set $\mathcal{C}$ is a typical example.
We consider the complement $X_{E}:=\widehat{\mathbb C}\setminus E$ of the Cantor set $E$.
It is an open Riemann surface with uncountable many boundary components.
We are interested in the quasiconformal equivalence of such surfaces.
In this talk, we discuss the quasiconformal equivalence for the complements of Cantor sets given by dynamical systems.
数値解析セミナー
16:50-18:20 数理科学研究科棟(駒場) 002号室
岡本久 氏 (学習院大学理学部)
Tosio Kato as an applied mathematician (Japanese)
岡本久 氏 (学習院大学理学部)
Tosio Kato as an applied mathematician (Japanese)
[ 講演概要 ]
Tosio Kato (1917-1999) is nowadays considered to be a rigorous analyst or theorist. Many people consider his contributions in quantum mechanics to be epoch-making, his work on nonlinear partial differential equations elegant and inspiring. However, around the time when he visited USA for the first time in 1954, he was studying problems of applied mathematics, too, notably numerical computation of eigenvalues. I wish to shed light on the historical background of his study of applied mathematics. This is a joint work with Prof. Hiroshi Fujita.
Tosio Kato (1917-1999) is nowadays considered to be a rigorous analyst or theorist. Many people consider his contributions in quantum mechanics to be epoch-making, his work on nonlinear partial differential equations elegant and inspiring. However, around the time when he visited USA for the first time in 1954, he was studying problems of applied mathematics, too, notably numerical computation of eigenvalues. I wish to shed light on the historical background of his study of applied mathematics. This is a joint work with Prof. Hiroshi Fujita.
2018年11月02日(金)
古典解析セミナー
17:00-18:30 数理科学研究科棟(駒場) 122号室
Giorgio Gubbiotti 氏 (The University of Sydney)
On the inverse problem of the discrete calculus of variations (ENGLISH)
Giorgio Gubbiotti 氏 (The University of Sydney)
On the inverse problem of the discrete calculus of variations (ENGLISH)
[ 講演概要 ]
One of the most powerful tools in Mathematical Physics since Euler and Lagrange is the calculus of variations. The variational formulation of mechanics where the equations of motion arise as the minimum of an action functional (the so-called Hamilton's principle), is fundamental in the development of theoretical mechanics and its foundations are present in each textbook on this subject [1, 3, 6]. Beside this, the application of calculus of variations goes beyond mechanics as many important mathematical problems, e.g. the isoperimetrical problem and the catenary, can be formulated in terms of calculus of variations.
An important problem regarding the calculus of variations is to determine which system of differential equations are Euler-Lagrange equations for some variational problem. This problem has a long and interesting history, see e.g. [4]. The general case of this problem remains unsolved, whereas several important results for particular cases were presented during the 20th century.
In this talk we present some conditions on the existence of a Lagrangian in the discrete scalar setting. We will introduce a set of differential operators called annihilation operators. We will use these operators to
reduce the functional equation governing of existence of a Lagrangian for a scalar difference equation of arbitrary even order 2k, with k > 1 to the solution of a system of linear partial differential equations. Solving such equations one can either find the Lagrangian or conclude that it does not exist.
We comment the relationship of our solution of the inverse problem of the discrete calculus of variation with the one given in [2], where a result analogous to the homotopy formula [5] for the continuous case was proven.
References
[1] H. Goldstein, C. Poole, and J. Safko. Classical Mechanics. Pearson Education, 2002.
[2] P. E. Hydon and E. L. Mansfeld. A variational complex for difference equations. Found. Comp. Math., 4:187{217, 2004.
[3] L. D. Landau and E. M. Lifshitz. Mechanics. Course of Theoretical Physics. Elsevier Science, 1982.
[4] P. J. Olver. Applications of Lie Groups to Differential Equations. Springer-Verlag, Berlin, 1986.
[5] M. M. Vainberg. Variational methods for the study of nonlinear operators. Holden-Day, San Francisco, 1964.
[6] E. T. Whittaker. A Treatise on the Analytical Dynamics of Particles and Rigid Bodies. Cambridge University Press, Cambridge, 1999.
One of the most powerful tools in Mathematical Physics since Euler and Lagrange is the calculus of variations. The variational formulation of mechanics where the equations of motion arise as the minimum of an action functional (the so-called Hamilton's principle), is fundamental in the development of theoretical mechanics and its foundations are present in each textbook on this subject [1, 3, 6]. Beside this, the application of calculus of variations goes beyond mechanics as many important mathematical problems, e.g. the isoperimetrical problem and the catenary, can be formulated in terms of calculus of variations.
An important problem regarding the calculus of variations is to determine which system of differential equations are Euler-Lagrange equations for some variational problem. This problem has a long and interesting history, see e.g. [4]. The general case of this problem remains unsolved, whereas several important results for particular cases were presented during the 20th century.
In this talk we present some conditions on the existence of a Lagrangian in the discrete scalar setting. We will introduce a set of differential operators called annihilation operators. We will use these operators to
reduce the functional equation governing of existence of a Lagrangian for a scalar difference equation of arbitrary even order 2k, with k > 1 to the solution of a system of linear partial differential equations. Solving such equations one can either find the Lagrangian or conclude that it does not exist.
We comment the relationship of our solution of the inverse problem of the discrete calculus of variation with the one given in [2], where a result analogous to the homotopy formula [5] for the continuous case was proven.
References
[1] H. Goldstein, C. Poole, and J. Safko. Classical Mechanics. Pearson Education, 2002.
[2] P. E. Hydon and E. L. Mansfeld. A variational complex for difference equations. Found. Comp. Math., 4:187{217, 2004.
[3] L. D. Landau and E. M. Lifshitz. Mechanics. Course of Theoretical Physics. Elsevier Science, 1982.
[4] P. J. Olver. Applications of Lie Groups to Differential Equations. Springer-Verlag, Berlin, 1986.
[5] M. M. Vainberg. Variational methods for the study of nonlinear operators. Holden-Day, San Francisco, 1964.
[6] E. T. Whittaker. A Treatise on the Analytical Dynamics of Particles and Rigid Bodies. Cambridge University Press, Cambridge, 1999.
2018年10月31日(水)
FMSPレクチャーズ
15:00-16:30 数理科学研究科棟(駒場) 122号室
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (4/4)
Lecture 4. BEYOND ELLIPTICITY or K-HOMOLOGY AND INDEX THEORY ON CONTACT MANIFOLDS (ENGLISH)
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (4/4)
Lecture 4. BEYOND ELLIPTICITY or K-HOMOLOGY AND INDEX THEORY ON CONTACT MANIFOLDS (ENGLISH)
[ 講演概要 ]
K-homology is the dual theory to K-theory. The BD (Baum-Douglas) isomorphism of Atiyah-Kasparov K-homology and K-cycle K-homology provides a framework within which the Atiyah-Singer index theorem can be extended to certain differential operators which are hypoelliptic but not elliptic. This talk will consider such a class of differential operators on compact contact manifolds. These operators have been studied by a number of mathematicians (e.g. C.Epstein and R.Melrose).
Operators with similar analytical properties have also been studied (e.g. by Alain Connes and Henri Moscovici --- also Michel Hilsum and Georges Skandalis). Working within the BD framework, the index problem will be solved for these differential operators on compact contact manifolds.
This is joint work with Erik van Erp.
[ 参考URL ]K-homology is the dual theory to K-theory. The BD (Baum-Douglas) isomorphism of Atiyah-Kasparov K-homology and K-cycle K-homology provides a framework within which the Atiyah-Singer index theorem can be extended to certain differential operators which are hypoelliptic but not elliptic. This talk will consider such a class of differential operators on compact contact manifolds. These operators have been studied by a number of mathematicians (e.g. C.Epstein and R.Melrose).
Operators with similar analytical properties have also been studied (e.g. by Alain Connes and Henri Moscovici --- also Michel Hilsum and Georges Skandalis). Working within the BD framework, the index problem will be solved for these differential operators on compact contact manifolds.
This is joint work with Erik van Erp.
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
早瀬友裕 氏 (東大数理)
Strong Tools in Free Probability Theory
早瀬友裕 氏 (東大数理)
Strong Tools in Free Probability Theory
2018年10月30日(火)
解析学火曜セミナー
16:50-18:20 数理科学研究科棟(駒場) 128号室
宮西吉久 氏 (大阪大学)
Spectral structure of the Neumann-Poincaré operator in three dimensions: Willmore energy and surface geometry (日本語)
宮西吉久 氏 (大阪大学)
Spectral structure of the Neumann-Poincaré operator in three dimensions: Willmore energy and surface geometry (日本語)
[ 講演概要 ]
The Neumann-Poincaré operator (abbreviated by NP) is a boundary integral operator naturally arising when solving classical boundary value problems using layer potentials. If the boundary of the domain, on which the NP operator is defined, is $C^{1, \alpha}$ smooth, then the NP operator is compact. Thus, the Fredholm integral equation, which appears when solving Dirichlet or Neumann problems, can be solved using the Fredholm index theory.
Regarding spectral properties of the NP operator, the spectrum consists of eigenvalues converging to $0$ for $C^{1, \alpha}$ smooth boundaries. Our main purpose here is to deduce eigenvalue asymptotics of the NP operators in three dimensions. This formula is the so-called Weyl's law for eigenvalue problems of NP operators. Then we discuss relationships among the Weyl's law, the Euler characteristic and the Willmore energy on the boundary surface.
The Neumann-Poincaré operator (abbreviated by NP) is a boundary integral operator naturally arising when solving classical boundary value problems using layer potentials. If the boundary of the domain, on which the NP operator is defined, is $C^{1, \alpha}$ smooth, then the NP operator is compact. Thus, the Fredholm integral equation, which appears when solving Dirichlet or Neumann problems, can be solved using the Fredholm index theory.
Regarding spectral properties of the NP operator, the spectrum consists of eigenvalues converging to $0$ for $C^{1, \alpha}$ smooth boundaries. Our main purpose here is to deduce eigenvalue asymptotics of the NP operators in three dimensions. This formula is the so-called Weyl's law for eigenvalue problems of NP operators. Then we discuss relationships among the Weyl's law, the Euler characteristic and the Willmore energy on the boundary surface.
PDE実解析研究会
10:30-11:30 数理科学研究科棟(駒場) 056号室
Piotr Rybka 氏 (University of Warsaw)
The least gradient problem in the plain (English)
Piotr Rybka 氏 (University of Warsaw)
The least gradient problem in the plain (English)
[ 講演概要 ]
The least gradient problem arises in many application, e.g. in the free material design. We show existence of solutions in bounded, strictly convex planar regions, when the data are functions on bounded variation.
Our main goal is to show existence of solution in convex, but not necessarily strictly convex planar regions. In order to avoid technicalities we consider only continuous data, but BV data will do to. We formulate a set of admissibility conditions. We show that they are sufficient for existence.
This is a joint project with Wojciech Górny and Ahmad Sabra.
The least gradient problem arises in many application, e.g. in the free material design. We show existence of solutions in bounded, strictly convex planar regions, when the data are functions on bounded variation.
Our main goal is to show existence of solution in convex, but not necessarily strictly convex planar regions. In order to avoid technicalities we consider only continuous data, but BV data will do to. We formulate a set of admissibility conditions. We show that they are sufficient for existence.
This is a joint project with Wojciech Górny and Ahmad Sabra.
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
志賀 啓成 氏 (東京工業大学)
The quasiconformal equivalence of Riemann surfaces and a universality of Schottky spaces (JAPANESE)
Tea: Common Room 16:30-17:00
志賀 啓成 氏 (東京工業大学)
The quasiconformal equivalence of Riemann surfaces and a universality of Schottky spaces (JAPANESE)
[ 講演概要 ]
In the theory of Teichmüller space of Riemann surfaces, we consider the set of Riemann surfaces which are quasiconformally equivalent. For topologically finite Riemann surfaces, it is quite easy to examine if they are quasiconformally equivalent or not. On the other hand, for Riemann surfaces of topologically infinite type, the situation is rather complicated.
In this talk, after constructing an example which shows the complexity of the problem, we give some geometric conditions for Riemann surfaces to be quasiconformally equivalent. Our argument enables us to see a universality of Schottky spaces.
In the theory of Teichmüller space of Riemann surfaces, we consider the set of Riemann surfaces which are quasiconformally equivalent. For topologically finite Riemann surfaces, it is quite easy to examine if they are quasiconformally equivalent or not. On the other hand, for Riemann surfaces of topologically infinite type, the situation is rather complicated.
In this talk, after constructing an example which shows the complexity of the problem, we give some geometric conditions for Riemann surfaces to be quasiconformally equivalent. Our argument enables us to see a universality of Schottky spaces.
統計数学セミナー
15:30-16:40 数理科学研究科棟(駒場) 126号室
Ciprian A. Tudor 氏 (Université de Lille 1, Université de Panthéon-Sorbonne Paris 1)
Asymptotic expansion for random vectors
Ciprian A. Tudor 氏 (Université de Lille 1, Université de Panthéon-Sorbonne Paris 1)
Asymptotic expansion for random vectors
[ 講演概要 ]
We develop the asymptotic expansion theory for vector-valued sequences $F_{N}$ of random variables. We find the second-order term in the expansion of the density of $F_{N}$, based on assumptions in terms of the convergence of the Stein-Malliavin matrix associated to the sequence $F_{N}$ . Our approach combines the classical Fourier approach and the recent theory on Stein method and Malliavin calculus. We find the second order term of the asymptotic expansion of the density of $F_{N}$ and we discuss the main ideas on higher order asymptotic expansion. We illustrate our results by several examples.
We develop the asymptotic expansion theory for vector-valued sequences $F_{N}$ of random variables. We find the second-order term in the expansion of the density of $F_{N}$, based on assumptions in terms of the convergence of the Stein-Malliavin matrix associated to the sequence $F_{N}$ . Our approach combines the classical Fourier approach and the recent theory on Stein method and Malliavin calculus. We find the second order term of the asymptotic expansion of the density of $F_{N}$ and we discuss the main ideas on higher order asymptotic expansion. We illustrate our results by several examples.
2018年10月29日(月)
東京確率論セミナー
16:00-17:30 数理科学研究科棟(駒場) 128号室
Sunder Sethuraman 氏 (University of Arizona)
On Hydrodynamic Limits of Young Diagrams (ENGLISH)
http://math.arizona.edu/~sethuram/
Sunder Sethuraman 氏 (University of Arizona)
On Hydrodynamic Limits of Young Diagrams (ENGLISH)
[ 講演概要 ]
We consider a family of stochastic models of evolving two-dimensional Young diagrams, given in terms of certain energies, with Gibbs invariant measures. `Static' scaling limits of the shape functions, under these Gibbs measures, have been shown by several over the years. The purpose of this article is to study corresponding `dynamical' limits of which less is understood. We show that the hydrodynamic scaling limits of the diagram shape functions may be described by different types of parabolic PDEs, depending on the energy structure.
The talk will be based on the article: https://arxiv.org/abs/1809.03592
[ 参考URL ]We consider a family of stochastic models of evolving two-dimensional Young diagrams, given in terms of certain energies, with Gibbs invariant measures. `Static' scaling limits of the shape functions, under these Gibbs measures, have been shown by several over the years. The purpose of this article is to study corresponding `dynamical' limits of which less is understood. We show that the hydrodynamic scaling limits of the diagram shape functions may be described by different types of parabolic PDEs, depending on the energy structure.
The talk will be based on the article: https://arxiv.org/abs/1809.03592
http://math.arizona.edu/~sethuram/
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
松村慎一 氏 (東北大学)
On morphisms of compact Kaehler manifolds with semi-positive holomorphic sectional curvature (JAPANESE)
松村慎一 氏 (東北大学)
On morphisms of compact Kaehler manifolds with semi-positive holomorphic sectional curvature (JAPANESE)
[ 講演概要 ]
In this talk, we consider a smooth projective variety $X$ with semi-positive holomorphic "sectional" curvature, motivated by generalizing Howard-Smyth-Wu's structure theorem and Mok's result for compact Kaehler manifold with semi-positive "bisectional" curvature.
We prove that, if $X$ admits a holomorphic maximally rationally connected fibration $X ¥to Y$, then the morphism is always smooth (that is, a submersion), that the image $Y$ admits a finite ¥'etale cover $T ¥to Y$ by a complex
torus $T$, and further that all the fibers $F$ are isomorphic.
This gives a structure theorem for $X$ when $X$ is a surface.
Moreover we show that $X$ is rationally connected, if the holomorphic sectional curvature is quasi-positive.
This result gives a generalization of Yau's conjecture.
In this talk, we consider a smooth projective variety $X$ with semi-positive holomorphic "sectional" curvature, motivated by generalizing Howard-Smyth-Wu's structure theorem and Mok's result for compact Kaehler manifold with semi-positive "bisectional" curvature.
We prove that, if $X$ admits a holomorphic maximally rationally connected fibration $X ¥to Y$, then the morphism is always smooth (that is, a submersion), that the image $Y$ admits a finite ¥'etale cover $T ¥to Y$ by a complex
torus $T$, and further that all the fibers $F$ are isomorphic.
This gives a structure theorem for $X$ when $X$ is a surface.
Moreover we show that $X$ is rationally connected, if the holomorphic sectional curvature is quasi-positive.
This result gives a generalization of Yau's conjecture.
FMSPレクチャーズ
15:00-16:30 数理科学研究科棟(駒場) 117号室
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (3/4)
Lecture 3. THE RIEMANN-ROCH THEOREM (ENGLISH)
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (3/4)
Lecture 3. THE RIEMANN-ROCH THEOREM (ENGLISH)
[ 講演概要 ]
Topics in this talk :
1. Classical Riemann-Roch
2. Hirzebruch-Riemann-Roch (HRR)
3. Grothendieck-Riemann-Roch (GRR)
4. RR for possibly singular varieties (Baum-Fulton-MacPherson)
[ 参考URL ]Topics in this talk :
1. Classical Riemann-Roch
2. Hirzebruch-Riemann-Roch (HRR)
3. Grothendieck-Riemann-Roch (GRR)
4. RR for possibly singular varieties (Baum-Fulton-MacPherson)
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
2018年10月26日(金)
談話会・数理科学講演会
15:30-16:30 数理科学研究科棟(駒場) 002号室
伊藤 健一 氏 (東京大学大学院数理科学研究科)
一般化固有関数の漸近挙動と散乱理論 (JAPANESE)
伊藤 健一 氏 (東京大学大学院数理科学研究科)
一般化固有関数の漸近挙動と散乱理論 (JAPANESE)
[ 講演概要 ]
散乱理論とは，入射波が障害物によって散乱される前後の挙動
を記述するための理論であり，物理における散乱実験などに数学的裏付けを与え
る理論である．本講演では量子散乱理論の数学的定式化について概説したのち，
講演者がErik Skibsted氏（Aarhus大学)との共同研究で得た結果の一部を紹介す
る．時間が許せば漸近的Euclid型や漸近的双曲型エンドを持つ多様体上への一般
化についても触れたい．
散乱理論とは，入射波が障害物によって散乱される前後の挙動
を記述するための理論であり，物理における散乱実験などに数学的裏付けを与え
る理論である．本講演では量子散乱理論の数学的定式化について概説したのち，
講演者がErik Skibsted氏（Aarhus大学)との共同研究で得た結果の一部を紹介す
る．時間が許せば漸近的Euclid型や漸近的双曲型エンドを持つ多様体上への一般
化についても触れたい．
2018年10月24日(水)
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
森迪也 氏 (東大数理)
The Mazur-Ulam property for unital C*-algebras (English)
森迪也 氏 (東大数理)
The Mazur-Ulam property for unital C*-algebras (English)
FMSPレクチャーズ
15:00-16:30 数理科学研究科棟(駒場) 123号室
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (2/4)
Lecture 2. THE DIRAC OPERATOR (ENGLISH)
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
Paul Baum 氏 (The Pennsylvania State University)
K-THEORY AND THE DIRAC OPERATOR (2/4)
Lecture 2. THE DIRAC OPERATOR (ENGLISH)
[ 講演概要 ]
The Dirac operator of R^n will be defined. This is a first order elliptic differential operator with constant coefficients.
Next, the class of differentiable manifolds which come equipped with an order one differential operator which (at the symbol level)is locally isomorphic to the Dirac operator of R^n will be considered. These are the Spin-c manifolds.
Spin-c is slightly stronger than oriented, so Spin-c can be viewed as "oriented plus epsilon". Most of the oriented manifolds that occur in practice are Spin-c. The Dirac operator of a closed Spin-c manifold is the basic example for the Hirzebruch-Riemann-Roch theorem and the Atiyah-Singer index theorem.
[ 参考URL ]The Dirac operator of R^n will be defined. This is a first order elliptic differential operator with constant coefficients.
Next, the class of differentiable manifolds which come equipped with an order one differential operator which (at the symbol level)is locally isomorphic to the Dirac operator of R^n will be considered. These are the Spin-c manifolds.
Spin-c is slightly stronger than oriented, so Spin-c can be viewed as "oriented plus epsilon". Most of the oriented manifolds that occur in practice are Spin-c. The Dirac operator of a closed Spin-c manifold is the basic example for the Hirzebruch-Riemann-Roch theorem and the Atiyah-Singer index theorem.
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Baum.pdf
2018年10月23日(火)
PDE実解析研究会
10:30-11:30 数理科学研究科棟(駒場) 056号室
Jian-Guo Liu 氏 (Duke University)
Least action principle for incompressible flow with free boundary (English)
Jian-Guo Liu 氏 (Duke University)
Least action principle for incompressible flow with free boundary (English)
[ 講演概要 ]
In this talk I will describe a connection between Arnold's least-action principle for incompressible flows with free boundary and geodesic paths for Wasserstein distance. The least-action problem for geodesic distance on the "manifold" of fluid-blob shapes exhibits instability due to microdroplet formation. Using a conformal map formulation we investigate singularity formation in water-wave dynamics neglecting gravity. A connection with fluid mixture models via a variant of Brenier's relaxed least-action principle for generalized Euler flows will also be discussed.
In this talk I will describe a connection between Arnold's least-action principle for incompressible flows with free boundary and geodesic paths for Wasserstein distance. The least-action problem for geodesic distance on the "manifold" of fluid-blob shapes exhibits instability due to microdroplet formation. Using a conformal map formulation we investigate singularity formation in water-wave dynamics neglecting gravity. A connection with fluid mixture models via a variant of Brenier's relaxed least-action principle for generalized Euler flows will also be discussed.
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
François Fillastre 氏 (Université de Cergy-Pontoise)
Co-Minkowski space and hyperbolic surfaces (ENGLISH)
Tea: Common Room 16:30-17:00
François Fillastre 氏 (Université de Cergy-Pontoise)
Co-Minkowski space and hyperbolic surfaces (ENGLISH)
[ 講演概要 ]
There are many ways to parametrize two copies of Teichmueller space by constant curvature -1 Riemannian or Lorentzian 3d manifolds (for example the Bers double uniformization theorem). We present the co-Minkowski space (or half-pipe space), which is a constant curvature -1 degenerated 3d space, and which is related to the tangent space of Teichmueller space. As an illustration, we give a new proof of a theorem of Thurston saying that, once the space of measured geodesic laminations on a compact hyperbolic surface is identified with the tangent space of Teichmueller space via infinitesimal earthquake, then the length of laminations is an asymmetric norm. Joint work with Thierry Barbot (Avignon).
There are many ways to parametrize two copies of Teichmueller space by constant curvature -1 Riemannian or Lorentzian 3d manifolds (for example the Bers double uniformization theorem). We present the co-Minkowski space (or half-pipe space), which is a constant curvature -1 degenerated 3d space, and which is related to the tangent space of Teichmueller space. As an illustration, we give a new proof of a theorem of Thurston saying that, once the space of measured geodesic laminations on a compact hyperbolic surface is identified with the tangent space of Teichmueller space via infinitesimal earthquake, then the length of laminations is an asymmetric norm. Joint work with Thierry Barbot (Avignon).
2018年10月22日(月)
東京確率論セミナー
16:00-17:30 数理科学研究科棟(駒場) 126号室
Trinh Khanh Duy 氏 (東北大学数理科学連携研究センター)
Limit theorems for random geometric complexes in the critical regime (ENGLISH)
Trinh Khanh Duy 氏 (東北大学数理科学連携研究センター)
Limit theorems for random geometric complexes in the critical regime (ENGLISH)
[ 講演概要 ]
Geometric complexes (eg. Cech complexes or Rips complexes) are simplicial complexes defined on a finite set of points in a Euclidean space together with a radius parameter, which can be viewed as a higher dimensional generalization of geometric graphs. This talk concerns with random geometric complexes built over binomial point processes (collections of iid points). Like random geometric graphs, there are three regimes (subcritical(or dust, sparse) regime, critical (or thermodynamic) regime and supercritical regime) which are divided according the growth of the radius parameters in which the limiting behavior of random geometric complexes is totally different. This talk introduces some results on the strong law of large numbers and a central limit theorem in the critical regime.
Geometric complexes (eg. Cech complexes or Rips complexes) are simplicial complexes defined on a finite set of points in a Euclidean space together with a radius parameter, which can be viewed as a higher dimensional generalization of geometric graphs. This talk concerns with random geometric complexes built over binomial point processes (collections of iid points). Like random geometric graphs, there are three regimes (subcritical(or dust, sparse) regime, critical (or thermodynamic) regime and supercritical regime) which are divided according the growth of the radius parameters in which the limiting behavior of random geometric complexes is totally different. This talk introduces some results on the strong law of large numbers and a central limit theorem in the critical regime.
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
足立真訓 氏 (静岡大学)
On certain hyperconvex manifolds without non-constant bounded holomorphic functions (JAPANESE)
足立真訓 氏 (静岡大学)
On certain hyperconvex manifolds without non-constant bounded holomorphic functions (JAPANESE)
[ 講演概要 ]
For each compact Riemann surface of genus > 1, we can construct a Riemann sphere bundle over the given Riemann surface using the projective structure induced by its uniformization.
The total space of this bundle is divided into two 1-convex domains by a closed Levi-flat real hypersurface. Although these two domains are not biholomorphic, we see that they have several function theoretic properties in common. In this talk, I would like to explain these common properties: hyperconvexity and expressions for certain Green function, and Liouville property and growth estimates of holomorphic functions.
For each compact Riemann surface of genus > 1, we can construct a Riemann sphere bundle over the given Riemann surface using the projective structure induced by its uniformization.
The total space of this bundle is divided into two 1-convex domains by a closed Levi-flat real hypersurface. Although these two domains are not biholomorphic, we see that they have several function theoretic properties in common. In this talk, I would like to explain these common properties: hyperconvexity and expressions for certain Green function, and Liouville property and growth estimates of holomorphic functions.
数値解析セミナー
16:50-18:20 数理科学研究科棟(駒場) 002号室
相原研輔 氏 (東京都市大学知識工学部)
短い漸化式を用いるクリロフ部分空間法に対する残差スムージング (Japanese)
相原研輔 氏 (東京都市大学知識工学部)
短い漸化式を用いるクリロフ部分空間法に対する残差スムージング (Japanese)
[ 講演概要 ]
クリロフ部分空間法は，大規模疎行列を係数に持つ連立一次方程式に有効な反復法群である．そのうち，Bi-CG法などの短い漸化式を用いる解法は，反復毎の計算量やメモリ使用量が少なく済むため，計算効率がよいが，生成される残差ノルムは振動する．残差ノルムが大きく振動すると，丸め誤差が拡大され，収束速度の低下や近似解精度の劣化に繋がる．そこで，収束性を改善するための残差スムージングについて取り上げる．古典的な残差スムージングは，残差ノルムの収束振る舞いを滑らかにするものの，丸め誤差の拡大を防ぐ効果はほとんどないことが知られている．一方，最近提案された相互作用型の残差スムージングは，丸め誤差の蓄積を抑制することができ，近似解精度が向上するなどの付加価値がある．本講演では，行列ベクトル積から発生する丸め誤差が収束性に与える影響を考察した上で，新旧の残差スムージングの効果の違いについて議論する．
クリロフ部分空間法は，大規模疎行列を係数に持つ連立一次方程式に有効な反復法群である．そのうち，Bi-CG法などの短い漸化式を用いる解法は，反復毎の計算量やメモリ使用量が少なく済むため，計算効率がよいが，生成される残差ノルムは振動する．残差ノルムが大きく振動すると，丸め誤差が拡大され，収束速度の低下や近似解精度の劣化に繋がる．そこで，収束性を改善するための残差スムージングについて取り上げる．古典的な残差スムージングは，残差ノルムの収束振る舞いを滑らかにするものの，丸め誤差の拡大を防ぐ効果はほとんどないことが知られている．一方，最近提案された相互作用型の残差スムージングは，丸め誤差の蓄積を抑制することができ，近似解精度が向上するなどの付加価値がある．本講演では，行列ベクトル積から発生する丸め誤差が収束性に与える影響を考察した上で，新旧の残差スムージングの効果の違いについて議論する．
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