今後の予定

過去の記録 ~04/18本日 04/19 | 今後の予定 04/20~

2019年04月22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
久本 智之 氏 (名古屋大学)
Optimal destabilizer for a Fano manifold (Japanese)
[ 講演概要 ]
Around 2005, S. Donaldson asked whether the lower bound of the Calabi functional is achieved by a sequence of the normalized Donaldson-Futaki invariants.
For a Fano manifold we construct a sequence of multiplier ideal sheaves from a new geometric flow and answer to Donaldson's question.

数値解析セミナー

16:50-18:20   数理科学研究科棟(駒場) 056号室
及川一誠 氏 (一橋大学大学院経営管理研究科)
HDG法の超収束について (Japanese)
[ 講演概要 ]
近年,hybridizable discontinuous Galerkin (HDG) 法の超収束性に関して研究が進展し,様々な結果が得られている.それらは大きく分けて,数値流束の安定化項に$L^2$射影を施すLehrenfeld-Sch{\" o}berl安定化と,HDG射影を用いるM-decomposition理論との2つに分類される.本講演では両者に関する概要を,講演者の研究結果を交えながら述べる.

離散数理モデリングセミナー

17:15-18:30   数理科学研究科棟(駒場) 118号室
Yuri Suris 氏 (Technische Universität Berlin)
Geometry of the Kahan-Hirota-Kimura discretization
[ 講演概要 ]
We will report on some novel results concerning the bilinear discretization of quadratic vector fields.

2019年04月23日(火)

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
Christine Vespa 氏 (Université de Strasbourg)
Higher Hochschild homology as a functor (ENGLISH)
[ 講演概要 ]
Higher Hochschild homology generalizes classical Hochschild homology for rings. Recently, Turchin and Willwacher computed higher Hochschild homology of a finite wedge of circles with coefficients in the Loday functor associated to the ring of dual numbers over the rationals. In particular, they obtained linear representations of the groups Out(F_n) which do not factorize through GL(n,Z).

In this talk, I will begin by recalling what is Hochschild homology and higher Hochschild homology. Then I will explain how viewing higher Hochschild homology of a finite wedge of circles as a functor on the category of free groups provides a conceptual framework which allows powerful tools such as exponential functors and polynomial functors to be used. In particular, this allows the generalization of the results of Turchin and Willwacher; this gives rise to new linear representations of Out(F_n) which do not factorize through GL(n,Z).

(This is joint work with Geoffrey Powell.)

2019年04月24日(水)

代数学コロキウム

17:30-18:30   数理科学研究科棟(駒場) 056号室
Joseph Ayoub 氏 (University of Zurich)
P^1-localisation and a possible definition of arithmetic Kodaira-Spencer classes (English)
[ 講演概要 ]
A^1-localisation is a universal construction which produces "cohomology theories" for which the affine line A^1 is contractible. It plays a central role in the theory of motives à la Morel-Voevodsky. In this talk, I'll discuss the analogous construction where the affine line is replaced by the projective line P^1. This is the P^1-localisation which is arguably an unnatural construction since it produces "cohomology theories" for which the projective line P^1 is contractible. Nevertheless, I'll explain a few positive results and some computations around this construction which naturally lead to a definition of Kodaira-Spencer classes of arithmetic nature. (Unfortunately, it is yet unclear if these classes are really interesting and nontrivial.)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 118号室
今学期は基本水曜日とします。部屋も去年度と異なります。
吉川翔 氏 (東大数理)
Varieties of dense globally F-split type with a non-invertible polarized
endomorphism
[ 講演概要 ]
Broustet and Gongyo conjectured that if a normal projective variety X has a non-invertible polaried endomorphism, then X is of Calabi-Yau type. Furthermore, Schwede and Smith conjectured that a projective variety is of Calabi-Yau type if and only if of dense globally F-split type. Therefore it is a natural question to ask if a normal projective variety X has a non-invertible polaried endomorphism, then X is of dense globally F-split type. In this talk, I will introduce simple points and difficult points of the question. Furthermore I will give the affirmative answer of my question for 2-dimensional case.

2019年04月25日(木)

応用解析セミナー

16:00-18:00   数理科学研究科棟(駒場) 118号室
この日は2つ講演があります.教室と時間にご注意下さい.
Matteo Muratori 氏 (Polytechnic University of Milan) 16:00-17:00
The porous medium equation on noncompact Riemannian manifolds with initial datum a measure
(English)
[ 講演概要 ]
We investigate existence and uniqueness of weak solutions of the Cauchy problem for the porous medium equation on Cartan-Hadamard manifolds. We show existence of solutions that take a finite Radon measure as initial datum, possibly sign-changing. We then prove uniqueness in the class of nonnegative solutions, upon assuming a quadratic lower bound on the Ricci curvature. Our result is "optimal" in the sense that any weak solution necessarily solves a Cauchy problem with initial datum a finite Radon measure. Moreover, as byproducts of the techniques we employ, we obtain some new results in potential analysis on manifolds, concerning the validity of a modified version of the mean-value inequality for superharmonic functions and related properties of potentials of positive Radon measures. Finally, we briefly discuss some work in progress regarding stability of the porous medium equation with respect to the Wasserstein distance, on Riemannian manifolds with Ricci curvature bounded below.
Maurizia Rossi 氏 (University of Pisa) 17:00-18:00
On sharp large deviations for the bridge of a general diffusion
(English)
[ 講演概要 ]
In this talk we provide sharp Large Deviation estimates for the probability of exit from a domain for the bridge of a d-dimensional general diffusion process X, as the conditioning time tends to 0. This kind of results is motivated by applications to numerical simulation. In particular we investigate the influence of the drift b of X. It turns out that the sharp asymptotics for the exit time probability are independent of the drift, provided b enjoyes a simple condition that is always satisfied in dimension 1. On the other hand, we show that the drift can be influential if this assumption is not satisfied. This talk is based on a joint work with P. Baldi and L. Caramellino.

情報数学セミナー

16:50-18:35   数理科学研究科棟(駒場) 128号室
夏学期は暗号理論の講演
岡本 龍明  氏 (NTT)
現代暗号の誕生と発展 (JAPANESE)
[ 講演概要 ]
現代暗号は40年ほど前に誕生したが、現在ではインターネットなどの安全性を保証する基盤技術として広く利用され、さらに応用面においても理論面でもこの10年余りの発展は著しい。
本セミナー(前期)では、このような現代暗号をその誕生から最近の発展まで、基本的暗号理論、ビットコインとブロックチェーン、ポスト量子暗号と格子暗号、完全準同型暗号、関数型暗号などを中心に、前提知識を必要としないで分かりやすく解説することをめざす(7, 8コマ程度)。
以上の講義の後に、高島克幸氏より楕円曲線に基づく暗号理論、とくに最近話題の同種写像暗号などを中心に解説して頂く(数コマ程度)。
まず、第1回(4月25日)では、現代暗号が誕生した経緯とそれらが現在どのような形で利用されているかについて紹介する。

2019年04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) 056号室
吉田善章 氏 (東京大学新領域創成科学研究科)
Lie-Poisson代数の「変形」とカイラルな場の理論 (日本語)
[ 講演概要 ]
物理の理論は「物」と「時空」の二つを使って記述される.物の特性は「エネルギー」の数学的表現(ハミルトニアン)に還元される.他方,時空の特性はその「幾何学」を特徴づける群の構造として定式化される.物の奇妙な運動(例えば回転方向に好き嫌い=カイラリティーをもつラトルバックというコマ)は,エネルギーが変な形をしているか,あるいは時空が変な法則をもっているかのいずれかに起因すると考えるのだが,ここでは後者の可能性を追求する.カイラリティー(Krein対称性の破れ)をもつPoisson多様体(Hamilton力学系)の構造を,その基底にあるLie代数の変形に帰着して考える理論を紹介する.

2019年04月30日(火)

代数学コロキウム

17:00-18:00   数理科学研究科棟(駒場) 122号室
Jean-Francois Dat 氏 (Sorbonne University)
Moduli space of l-adic Langlands parameters and the stable Bernstein center (English)
[ 講演概要 ]
Motivated by the description of the integral l-adic cohomology of certain Shimura varieties in middle degree, Emerton and Helm have conjectured the existence of a certain local Langlands correspondence for l-adic families of n-dimensional Galois representations. The proof of this conjecture by Helm and Moss relies on a beautiful isomorphism between the ring of functions of the moduli space of l-adic representations and the integral Bernstein center of GL_n(F). We will present a work in progress with Helm, Korinczuk and Moss towards a generalization of this result for arbitrary (tamely ramified) reductive groups.

2019年05月08日(水)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 118号室
橋詰 健太 氏 (東大数理)
TBA
[ 講演概要 ]
TBA

2019年05月13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
只野 誉 氏 (東京理科大学)

数値解析セミナー

16:50-18:20   数理科学研究科棟(駒場) 056号室
相島健助 氏 (法政大学情報科学部)
対称固有値問題に対する反復改良法 (Japanese)
[ 講演概要 ]
本講演では,対称行列の固有値問題の数値解法について議論する.具体的には,対称固有値問題のすべての固有値と固有ベクトルの近似値が得られている場合に,さらに精度を上げるための反復改良法を提案しその収束理論を与える.

対称固有値問題のすべての固有値と固有ベクトルを計算する場合,後退誤差解析の意味で数値的に安定な手法が既に確立されており,数値線形代数の標準ライブラリLAPACK或いはMATLABのような汎用ソフトにも実装され広く利用されている.ただし,悪条件問題において固有ベクトルの数値計算は原理的に困難であることには注意を要する.この困難に対し,本研究で提案する適合的に計算精度を変更しながら行う反復改良法は一つの有力な技術になりうる.また主要計算部分が行列積で表現でき,この性質は実装面での長所となる.本講演では,提案手法の着想や導出過程そして数値的な性能と二次収束性の証明について述べる.本研究は荻田武史氏(東京女子大学)との共同研究である.

2019年05月14日(火)

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
J. Scott Carter 氏 (University of South Alabama, 大阪市立大学)
Diagrammatic Algebra (ENGLISH)
[ 講演概要 ]
Three main ideas will be explored. First, a higher dimensional category (a category that has arrows, double arrows, triple arrows, and quadruple arrows) that is based upon the axioms of a Frobenius algebra will be outlined. Then these structures will be promoted into one higher dimension so that braiding can be introduced. Second, relationships between braiding and multiplication will be studied from a homological perspective. Third, the next order relations will be used to formulate a system of abstract tensor equations that are analogous to the Yang-Baxter relation. In this way, a broad outline of the notion of diagrammatic algebra will be presented.

2019年05月15日(水)

FMSPレクチャーズ

17:30-18:30   数理科学研究科棟(駒場) 122号室
*The date and room have changed.
Gábor Domokos 氏 (Hungarian Academy of Sciences/Budapest University of Technology and Economics)
'Oumuamua, the Gömböc and the Pebbles of Mars (ENGLISH)
[ 講演概要 ]
In this talk I will concentrate on two examples from planetary science, which made the headlines in recent years to highlight the power and significance of nonlinear geometric partial differential equations (PDEs) explaining puzzles presented by Nature. One key link between PDE theory of shape evolution and natural phenomena is the Gömböc, the first mono-monostatic object whose existence was first conjectured by V.I. Arnold in 1995. I will explain the connection and illustrate the process how mathematical models of Nature may be identified.
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Domokos.pdf

FMSPレクチャーズ

15:00-17:20   数理科学研究科棟(駒場) 122号室
J. Scott Carter 氏 (University of South Alabama / Osaka City University)
Part 1 : Categorical analogues of surface singularities
Part 2 : Prismatic Homology (ENGLISH)
[ 講演概要 ]
Part 1 :
Isotopy classes of surfaces that are embedded in 3-space can be described as a free 4-category that has one object and one weakly invertible arrow. That description coincides with a fundamental higher homotopy group. The surface singularities that correspond to cusps and optimal points on folds can be used to develop categorical analogues of swallow-tails and horizontal cusps. In this talk, the 4-category will be constructed from the ground up, and the general structure will be described.

Part 2 :
A qualgebra is a set that has two binary operations whose relationships to each other are similar to the relations between group multiplication and conjugation. The axioms themselves are described in terms of isotopies of knotted trivalent graphs and the handle-body knots that are represented. The moves naturally live in prisms. By using a generalization of the tensor product of chain complexes, a homology theory is presented that encapsulates these axioms and the higher order relations between them. We show how to use this homology theory to give a solution a system of tensor equations related to the Yang-Baxter relation.
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Carter.pdf

2019年05月20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
奥間 智弘 氏 (山形大学)

2019年05月27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
小池 貴之 氏 (大阪市立大学)

2019年05月29日(水)

代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 118号室
今学期は基本水曜日とします。部屋も去年度と異なります。
江辰 氏 (Fudan/MSRI)
TBA (English)
[ 講演概要 ]
TBA

2019年06月10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
Andrei Pajitnov 氏 (ナント大学)
(English)

2019年06月11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
Antonio De Rosa 氏 (クーラン数理科学研究所)
Solutions to two conjectures in branched transport: stability and regularity of optimal paths (English)
[ 講演概要 ]
Models involving branched structures are employed to describe several supply-demand systems such as the structure of the nerves of a leaf, the system of roots of a tree and the nervous or cardiovascular systems. The transportation cost in these models is proportional to a concave power $\alpha \in (0,1)$ of the intensity of the flow. We focus on the stability of the optimal transports, with respect to variations of the source and target measures. The stability was known when $\alpha$ is bigger than a critical threshold, but we prove it for every exponent $\alpha \in (0,1)$ and we provide a counterexample for $\alpha=0$. Thus we completely solve a conjecture of the book Optimal transportation networks by Bernot, Caselles and Morel. Moreover the robustness of our proof allows us to get the stability for more general lower semicontinuous functional. Furthermore, we prove the stability for the mailing problem, which was completely open in the literature, solving another conjecture of the aforementioned book. We use the latter result to show the regularity of the optimal networks. (Joint works with Maria Colombo and Andrea Marchese)

2019年06月24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
山盛 厚伺 氏 (工学院大学)
(Japanese)