Seminar information archive

Seminar information archive ~05/21Today's seminar 05/22 | Future seminars 05/23~

thesis presentations

11:00-12:15   Room #122 (Graduate School of Math. Sci. Bldg.)
ASAKA Takeru (Graduate School of Mathematical Sciences University of Tokyo)
Earthquake theorem and cluster algebras
(地震定理とクラスター代数)

thesis presentations

11:00-12:15   Room #126 (Graduate School of Math. Sci. Bldg.)
HAYASHI Kohei (Graduate School of Mathematical Sciences University of Tokyo)
On universality of the Kardar-Parisi-Zhang equation in high temperature regime
(高温相におけるKardar-Parisi-Zhang 方程式の普遍性について)

thesis presentations

13:00-14:15   Room #118 (Graduate School of Math. Sci. Bldg.)
WANG LONG (Graduate School of Mathematical Sciences University of Tokyo)
Studies on the Cone Conjecture, Automorphisms, and Arithmetic Degrees
(錐予想, 自己同型と算術次数の研究)

thesis presentations

13:00-14:15   Room #122 (Graduate School of Math. Sci. Bldg.)
KIM Minkyu (Graduate School of Mathematical Sciences University of Tokyo)
Finite path integral model and toric code based on homological algebra
(ホモロジー代数に基づく有限経路積分モデルとトーリックコード)

thesis presentations

14:45-16:00   Room #118 (Graduate School of Math. Sci. Bldg.)
TSURUSAKI Hisanori (Graduate School of Mathematical Sciences University of Tokyo)
Irreducible module decompositions of rank 2 symmetric hyperbolic Kac-Moody Lie algebras by sl2 subalgebras which are generalizations of principal sl2 subalgebras
(主sl2部分代数の一般化であるsl2部分代数によるrank2対称双曲型Kac-Moody Lie 代数の既約分解)

2023/01/20

Colloquium

15:30-16:30   Hybrid
If you do not belong to Graduate School of Mathematical Sciences, the University of Tokyo, please take part online [Reference URL].
Mikhail Bershtein (HSE University, Skoltech)
Kyiv formula and its applications (ENGLISH)
[ Abstract ]
The Kyiv formula gives the generic tau function of Painleve' equation (and more generally isomonodromy deformation equations) in terms of conformal blocks or Nekrasov partition function. I will explain the statement, examples and different approaches to the proof. If time permits, I will discuss some applications of this formula.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tZUrduioqjouG9wBfhl35VPxN_K92oa1wB4P

Tokyo-Nagoya Algebra Seminar

10:30-12:00   Online
Please see the reference URL for details on the online seminar.
Shunsuke Kano (Tohoku University)
Tropical cluster transformations and train track splittings (Japanese)
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

2023/01/19

Information Mathematics Seminar

16:50-18:35   Room #123 (Graduate School of Math. Sci. Bldg.)
Shintaro Narisada (KDDI Research, Inc.)
Code-based cryptography and its decoding algorithm (Japanese)
[ Abstract ]
This talk overviews code-based cryptography and its decoding algorithm called Information Set Decoding (ISD). All lectures will be given in Japanese.

2023/01/18

Number Theory Seminar

17:00-18:00   Hybrid
Kestutis Cesnavicius (Paris-Saclay University)
The affine Grassmannian as a presheaf quotient (English)
[ Abstract ]
The affine Grassmannian of a reductive group G is usually defined as the étale sheafification of the quotient of the loop group LG by the positive loop subgroup. I will discuss various triviality results for G-torsors which imply that this sheafification is often not necessary.

2023/01/17

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Chenghan Zha (The Univesity of Tokyo)
Integral structures in the local algebra of a singularity (ENGLISH)
[ Abstract ]
We compute the image of the Milnor lattice of an ADE singularity under a period map. We also prove that the Milnor lattice can be identified with an appropriate relative K-group defined through the Berglund-Huebsch dual of the corresponding singularity. Furthermore, we figure out the image of the Milnor lattice of the singularity of an invertible polynomial of chain type using the basis of middle homology constructed by Otani-Takahashi. We calculated the Seifert form of the basis as well.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2023/01/16

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Takayuki Koike (Osaka Metropolitan University)
Holomorphic foliation associated with a semi-positive class of numerical dimension one (Japanese)
[ Abstract ]
Let $X$ be a compact Kähler manifold and $\alpha$ be a Dolbeault cohomology class of bidegree $(1,1)$ on $X$.
When the numerical dimension of $\alpha$ is one and $\alpha$ admits at least two smooth semi-positive representatives, we show the existence of a family of real analytic Levi-flat hypersurfaces in $X$ and a holomorphic foliation on a suitable domain of $X$ along whose leaves any semi-positive representative of $\alpha$ is zero.

As an application, we give the affirmative answer to a conjecture on the relation between the semi-positivity of the line bundle $[Y]$ and the analytic structure of a neighborhood of $Y$ for a smooth connected hypersurface $Y$ of $X$.

As an application, we give the affirmative answer to a conjecture on the relation between the semi-positivity of the line bundle $[Y]$ and the analytic structure of a neighborhood of $Y$ for a smooth connected hypersurface $Y$ of $X$.
[ Reference URL ]
https://forms.gle/hYT2hVhDE3q1wDSh6

2023/01/13

Discrete mathematical modelling seminar

13:15-14:45   Room #126 (Graduate School of Math. Sci. Bldg.)
Andy Hone (University of Kent)
An infinite sequence of Heron triangles with two rational medians (English)
[ Abstract ]
Triangles with integer length sides and integer area are known as Heron triangles. Taking rescaling freedom into account, one can apply the same name when all sides and the area are rational numbers. A perfect triangle is a Heron triangle with all three medians being rational, and it is a longstanding conjecture that no such triangle exists. However, despite an assertion by Schubert that even two rational medians are impossible, Buchholz and Rathbun showed that there are infinitely many Heron triangles with two rational medians, an infinite subset of which are associated with rational points on an elliptic curve E(Q) with Mordell-Weil group Z x Z/2Z, and they observed a connection with a pair of Somos-5 sequences. Here we make the latter connection more precise by providing explicit formulae for the integer side lengths, the two rational medians, and the area in this infinite family of Heron triangles. The proof uses a combined approach to Somos-5 sequences and associated Quispel-Roberts-Thompson (QRT) maps in the plane, from several different viewpoints: complex analysis, real dynamics, and reduction modulo a prime.

2023/01/12

Information Mathematics Seminar

16:50-18:35   Room #123 (Graduate School of Math. Sci. Bldg.)
Yasunari Suzuki (NTT)
Theory of fault-tolerant quantum computing II (Japanese)
[ Abstract ]
To demonstrate reliable quantum computing, we need to integrate
quantum error correction techniques and achieve fault-tolerant quantum
computing. In this seminar, I will explain the basics of fault-tolerant quantum
computing and recent progress toward its experimental realization.

Lectures

16:00-17:00   Online
Prof. Yi-Hsuan Lin (National Yang Ming Chiao Tung University, Taiwan)
The Calder'on problem for nonlocal parabolic operators (English)
[ Abstract ]
We investigate inverse problems in the determination of leading coefficients for nonlocal parabolic operators, by knowing the corresponding Cauchy data in the exterior space-time domain. The key contribution is that we reduce nonlocal parabolic inverse problems to the corresponding local inverse problems with the lateral boundary Cauchy data. In addition, we derive a new equation and offer a novel proof of the unique continuation property for this new equation. We also build both uniqueness and non-uniqueness results for both nonlocal isotropic and anisotropic parabolic Calder'on problems, respectively.
This is a joint work with Ching-Lung Lin and Gunther Uhlmann.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/j/82806510515?pwd=NEk1RDlMVEFOTEg4WE1MekRySlJpdz09

2023/01/11

Discrete mathematical modelling seminar

13:15-16:45   Room #056 (Graduate School of Math. Sci. Bldg.)
Joe Harrow (University of Kent) 13:15-14:45
Determinantal expressions for Ohyama polynomials (English)
[ Abstract ]
The Ohyama polynomials provide algebraic solutions of the D7 case of the Painleve III equation at a particular sequence of parameter values. It is known that many special function solutions of Painleve equations are expressed in terms of tau functions that can be written in the form of determinants, but until now such a representation for the Ohyama polynomials was not known. Here we present two different determinantal formulae for these polynomials: the first, in terms of Wronskian determinants related to a Darboux transformation for a Lax pair of KdV type; and the second, in terms of Hankel determinants, which is related to the Toda lattice. If time permits, then connections with orthogonal polynomials, and with the recent Riemann-Hilbert approach of Buckingham & Miller, will briefly be mentioned.
Andy Hone (University of Kent) 15:15-16:45
Discrete dynamics, continued fractions and hyperelliptic curves (English)
[ Abstract ]
After reviewing some standard facts about continued fractions for quadratic irrationals, we switch from the real numbers to the field of Laurent series, and describe some classical and more recent results on continued fraction expansions for the square root of an even degree polynomial, and other functions defined on the associated hyperelliptic curve. In the latter case, we extend results of van der Poorten on continued fractions of Jacobi type (J-fractions), and explain the connection with a family of discrete integrable systems (including Quispel-Roberts-Thompson maps and Somos sequences), orthogonal polynomials, and the Toda lattice. If time permits, we will make some remarks on current work with John Roberts and Pol Vanhaecke, concerning expansions involving the square root of an odd degree polynomial, Stieltjes continued fractions, and the Volterra lattice.

2023/01/10

Algebraic Geometry Seminar

10:30-12:00   Room #ハイブリッド開催/002 (Graduate School of Math. Sci. Bldg.)
Akihiro Higashitani (Osaka/Dept. of Inf. )
Toric Fano varieties arising from posets and their combinatorial mutation equivalence (日本語)
[ Abstract ]
In 1986, Stanley introduced two polytopes arising from posets, called order polytopes and chain polytopes. Since then, those polytopes have been studied from viewpoints of combinatorics. Projective toric varieties arising from order polytopes are called Hibi toric varieties in these days. On the other hand, combinatorial mutations were introduced by Akhtar-Coates-Galkin-Kasprzyk in 2012 in the context of the classification problem of Fano varieties using mirror symmetry.
In this talk, after surveying two poset polytopes and combinatorial mutations, we discuss the combinatorial mutation equivalence of two poset polytopes. Those equivalence implies qG-deformation equivalence of projective toric varieties arising from two poset polytopes.
Moreover, it turns out that order polytopes, chain polytopes and their intermediate polytopes correspond to some toric Fano varieties.

Lectures

16:00-17:00   Online
Professor Salah-Eddine CHORFI (Cadi Ayyad University, Faculty of Sciences, Morocco)
Logarithmic convexity of semigroups and inverse problems for parabolic equations (English)
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/j/83149935801?pwd=OE5aanNBVGxvajNycXgyb2RKcW1kZz09

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Takeru Asaka (The Univesity of Tokyo)
Some calculations of an earthquake map in the cross ratio coordinates and the earthquake theorem of cluster algebras of finite type (JAPANESE)
[ Abstract ]
Thurston defined an earthquake, which cuts the Poincaré half-plane model and shifts it. Though it is a discontinuous bijective map, it can be extended to a homeomorphism of a circumference. Also, if an earthquake is equivalent relative to a Fuchsian group, the homeomorphism is equivalent, too. Moreover, Thurston proved the earthquake theorem saying that there uniquely exists an earthquake for any orient-preserving homeomorphism of a circumference, and Bonsante-Krasnov-Schlenker extended it to the case of marked surfaces. We calculate some earthquake maps by the cross ratio coordinates. The cross ratio coordinates are deeply related by the cluster algebra (Fock-Goncharov). We prove the earthquake theorem of cluster algebras of finite type. It is a joint work with Tsukasa Ishibashi and Shunsuke Kano.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Seminar on Probability and Statistics

10:50-11:30   Room # (Graduate School of Math. Sci. Bldg.)
井口優雅 (University College London)
Parameter Estimation with Increased Precision for Elliptic and Hypo-elliptic Diffusions

[ Abstract ]
Parametric inference for multi-dimensional diffusion processes has been studied over the past decades. Established approaches for likelihood-based estimation invoke a numerical time-discretisation scheme for the approximation of the (typically intractable) transition dynamics of the Stochastic Differential Equation (SDE) over finite time periods. Especially in the setting of some class of hypo-elliptic models, recent research (Ditlevsen and Samson 2019, Gloter and Yoshida 2021) has highlighted the critical effect of the choice of numerical scheme on the behaviour of derived parameter estimates. In our work, first, we develop two weak second order ‘sampling schemes' (to cover both the hypo-elliptic and elliptic classes) and generate accompanying ‘transition density schemes' of the SDE (i.e., approximations of the SDE transition density). Then, we produce a collection of analytic results, providing a complete theoretical framework that solidifies the proposed schemes and showcases advantages from their incorporation within SDE calibration methods, in both high and low frequency observations regime. We also present numerical results from carrying out classical or Bayesian inference. This is a joint work with Alexandros Beskos and Matthew Graham, and the preprint is available at https://arxiv.org/abs/2211.16384.
[ Reference URL ]
(現地参加) https://forms.gle/qwssLccVgsAWcfps7                                 (Zoom参加) (1/8迄)     https://docs.google.com/forms/d/e/1FAIpQLSe7OYeMDfaZ7pTLO42k43Tn5dWKpsyw

2023/01/04

Number Theory Seminar

17:00-18:00   Hybrid
Kazuhiro Ito (The University of Tokyo, Kavli IPMU)
G-displays over prisms and deformation theory (Japanese)
[ Abstract ]
The notion of display, which was introduced by Zink, has been successfully applied to the deformation theory of p-divisible groups. Recently, for a reductive group G over the ring of p-adic integers, Lau introduced the notion of G-display. In this talk, following the approach of Lau, we study displays and G-displays over the prismatic site of Bhatt-Scholze, and explain the deformation theory for them. As an application, we give an alternative proof of the classification of p-divisible groups over a complete discrete valuation ring of mixed characteristic (0, p) with perfect residue field, using our deformation theory.

Lectures

17:00-18:00   Online
Professor Debora Presti (Messina University)
On the source of the catastrophic 1908 Messina tsunami, southern Italy (English)
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/j/81296515694?pwd=dlNZY2dZWDRENmdscjRWcFM1MjRCQT09

2022/12/27

Lectures

16:00-17:00   Online
Professor Salah-Eddine CHORFI (Cadi Ayyad University, Faculty of Sciences, Morocco)
Controllability and inverse problems for parabolic equations with dynamic boundary conditions. (English)
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/j/83149935801?pwd=OE5aanNBVGxvajNycXgyb2RKcW1kZz09

2022/12/22

Information Mathematics Seminar

16:50-18:35   Room #123 (Graduate School of Math. Sci. Bldg.)
Yasunari Suzuki (NTT)
Theory of fault-tolerant quantum computing I (Japanese)
[ Abstract ]
To demonstrate reliable quantum computing, we need to integrate quantum error correction techniques and achieve fault-tolerant quantum computing. In this seminar, I will explain the basic of fault-tolerant quantum computing and recent progress towards its experimental realization.

2022/12/21

Algebraic Geometry Seminar

13:00-14:00 or 14:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
The room is different from the usual place. This is a joint seminar with Kyoto University.
Hsueh-Yung Lin (NTU)
Towards a geometric origin of the dynamical filtrations (English)
[ Abstract ]
Let X be a smooth projective variety with an automorphism f. When X is a threefold, Serge Cantat asked whether X has a non-trivial equivariant rational fibration, if the action of f on the Néron-Severi space is non-trivial and unipotent. We will propose a precise conjecture related to Cantat's question for minimal varieties in arbitrary dimension, in light of the "dynamical filtrations" arising in the study of zero entropy group actions. This conjecture also suggests a geometric origin of dynamical filtrations, whose definition is purely cohomological. We will provide some heuristic evidence from the relative abundance conjecture.
If time permits, we will also explain how the study of dynamical filtrations leads to new results about solvable group actions, which are not necessarily of zero entropy.

2022/12/20

Algebraic Geometry Seminar

9:30-10:30   Room #オンラインZoom (Graduate School of Math. Sci. Bldg.)
Takumi Murayama (Purdue)
The relative minimal model program for excellent algebraic spaces and analytic spaces in equal characteristic zero (English)
[ Abstract ]
In 2010, Birkar, Cascini, Hacon, and McKernan proved a relative version of the minimal model program for projective morphisms of complex quasi-projective varieties, called the relative minimal model program with scaling. Their result is now fundamental to our understanding of the birational classification of quasi-projective varieties and has numerous applications.
In this talk, I will discuss recent joint work with Shiji Lyu that establishes the relative minimal model program with scaling for excellent schemes, excellent algebraic spaces, and analytic spaces simultaneously in equal characteristic zero. This not only recovers previous results for complex varieties, complex algebraic spaces, and complex analytic spaces, but also greatly extends the scope of the relative minimal model program with scaling to a broader class of geometric spaces, including formal schemes, rigid analytic spaces, and Berkovich spaces, all in equal characteristic zero. Our results for (non-algebraic) schemes and rigid analytic spaces were previously only known in dimensions ≤3 and ≤2, respectively, and our results for formal schemes and Berkovich spaces are completely new.

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