Seminar information archive

Seminar information archive ~03/04Today's seminar 03/05 | Future seminars 03/06~

2023/12/07

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Ryo Nishimaki (NTT)
Cryptographic Program Obfuscation and Its Applications (Japanese)
[ Abstract ]
I will explain what cryptographically secure program obfuscation is, how to achieve it, and its applications in this talk.

2023/12/06

Infinite Analysis Seminar Tokyo

13:00-14:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Misha Feigin (University of Glasgow)
This seminar has been cancelled.

Flat coordinates of algebraic Frobenius manifolds (ENGLISH)
[ Abstract ]
This seminar has been cancelled.

Orbit spaces of the reflection representation of finite irreducible Coxeter groups provide Frobenius manifolds with polynomial prepotentials. Flat coordinates of the corresponding flat metric, known as Saito metric, are distinguished basic invariants of the Coxeter group. They have applications in representations of Cherednik algebras. Frobenius manifolds with algebraic prepotentials remain not classified and they are typically related to quasi-Coxeter conjugacy classes in finite Coxeter groups. We obtain flat coordinates for the majority of known examples of algebraic Frobenius manifolds in dimensions up to 4. In all the cases, flat coordinates appear to be some algebraic functions on the orbit space of the Coxeter group. This is a joint work with Daniele Valeri and Johan Wright.

2023/12/05

Tuesday Seminar on Topology

17:00-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Teruaki Kitano (Soka University)
On the Euler class for flat S1-bundles, C vs Cω (JAPANESE)
[ Abstract ]
We describe low dimensional homology groups of the real analytic, orientation preserving diffeomorphism group of S1 in terms of BΓ1 by applying a theorem of Thurston. It is an open problem whether some power of the rational Euler class vanishes for real analytic flat S1 bundles. In this talk we discuss that if it does, then the homology group should contain many torsion classes that vanish in the smooth case. Along this line we can give a new proof for the non-triviality of any power of the rational Euler class in the smooth case. If time permits, we will mention some attempts to study a Mather-Thurston map in the analytic case. This talk is based on a joint work with Shigeyuki Morita and Yoshihiko Mitsumatsu.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2023/12/04

FJ-LMI Seminar

14:00-   Room #056 (Graduate School of Math. Sci. Bldg.)
Philippe G. LEFLOCH (Sorbonne University & CNRS)
An introduction to Einstein constraints and the seed-to-solution method
[ Abstract ]
I will present an introduction to the constraint equations associated with Einstein’s field equations of general relativity, and to recent developments based on the seed-to-solution method developed in collaboration with The-Cang Nguyen (Montpellier) and Bruno Le Floch (LPTHE, Sorbonne).
[ Reference URL ]
https://fj-lmi.cnrs.fr/seminars/

2023/11/30

Applied Analysis

16:00-17:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Philippe G. LeFloch (Sorbonne University and CNRS)
Einstein spacetimes: dispersion, localization, collapse, and bouncing (English)
[ Abstract ]
I will overview recent developments on Einstein's field equations of general relativity, especially the global evolution problem from initial data sets. A variety of phenomena may arise in this evolution: gravitational waves, dispersion, collapse, formation of singularities, and bouncing. While many problems remain widely open and very challenging, in the past decades major mathematical advances were made for several classes of spacetimes. I will review recent results on the (1) nonlinear stability of Minkowski spacetime, (2) localization problem at infinity, (3) collapse of spherically symmetric fields, and (4) scattering through quiescent singularity. This talk is based on joint work with Y. Ma (Xi'an), T.-C. Nguyen (Montpellier), F. Mena (Lisbon), B. Le Floch (Paris), and G. Veneziano (Geneva).
Blog: philippelefloch.org
[ Reference URL ]
https://forms.gle/HPsYinKweUW3AQGv9

2023/11/28

Tuesday Seminar on Topology

17:00-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Gwénaël Massuyeau (Université de Bourgogne)
An analogue of the Johnson-Morita theory for the handlebody group (ENGLISH)
[ Abstract ]
The Johnson-Morita theory provides an approach for the mapping class group of a surface by considering its actions on the successive nilpotent quotients of the fundamental group of the surface. In this talk, after an outline of the original theory, we will present an analogue of the Johnson-Morita theory for the handlebody group, i.e. the mapping class group of a handlebody. This is joint work with Kazuo Habiro; as we shall explain if time allows, our motivation is to recover the "tree reduction" of a certain functor on the category of bottom tangles in handlebodies that we introduced (a few years ago) using the Kontsevich integral.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

FJ-LMI Seminar

16:00-   Room #117 (Graduate School of Math. Sci. Bldg.)
Maud DELATTRE (Université Paris-Saclay, INRAE)
Some contributions on variable selection in nonlinear mixed-effects models
[ Abstract ]
In the first part of this presentation, we will introduce the general formalism of nonlinear mixed effects models (NLMEM) that are specifically designed models to describe dynamic phenomena from repeated data on several subjects. In the second part, we will focus on specific variable selection technics for NLMEM through two contributions. In the first one, we will discuss the proper definition and use of the Bayesian information criterion (BIC) for variable selection in a low dimensional setting. High dimensional variable selection is the subject of the second contribution.

References
[1] Delattre, M., Lavielle, M. and Poursat, M.A. (2014) A note on BIC in mixed effects models, Electronic Journal of Statistics 8(1) p. 456-475.
[2] Delattre, M. and Poursat, M.A. (2020) An iterative algorithm for joint covariate and random effect selection in mixed effects models., The International Journal of Biostatistics 16(2), 20190082.
[3] Naveau, M., Kon Kam King, G., Rincent, R., Sansonnet, L. and Delattre, M. Bayesian high dimensional covariate selection in non-linear mixed-effects models using the SAEM algorithm. hal-03685060.
[ Reference URL ]
https://fj-lmi.cnrs.fr/seminars/

2023/11/27

Seminar on Geometric Complex Analysis

11:00-12:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Satoshi Ogawa (Osaka Metropolitan University)
On a holomorphic tubular neighborhood of a compact complex curve and Brjuno condition (Japanese)
[ Abstract ]
Let $C$ be a compact complex curve holomorphically embedded in a non-singular complex surface $M$ with a unitary flat normal bundle $N_{C/M}$ and let $\mathcal{U}$ be a finite open cover of $C$. Gong--Stolovitch posed a sufficient condition for the existence of a holomorphic tubular neighborhood of $C$ in $M$ expressed with operator norms of Čech coboundary maps $\delta$ on $\check{C}^0(\mathcal{U}, \mathcal{O}_C(N_{C/M}^\nu))$ and $\check{C}^0(\mathcal{U}, \mathcal{O}_C(T_C \otimes N_{C/M}^\nu))$.
In this talk, we introduce some estimates of the operator norms of $\delta$. As a result, we see the Brjuno condition appears as a sufficient condition for the existence of a holomorphic tubular neighborhood.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tZEqceqsrTIjEtRxenSMdPogvCxlWzAogj5A

Tokyo Probability Seminar

17:00-18:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Stefan Junk (学習院大学)
Local limit theorem for directed polymer in (almost) the whole weak disorder regime (English)
[ Abstract ]
We consider the directed polymer model in the weak disorder (high temperature) phase in spatial dimension d>2. In the case where the (normalized) partition function is L^2-bounded it is known for that time
polymer measure satisfies a local limit theorem, i.e., that the point-to-point partition function can be approximated by two point-to-plane partition functions at the start- and endpoint. We show
that this result continues to hold true if the partition function is L^p-bounded for some p>1+2/d. We furthermore show that for environments with finite support the required L^p -boundedness holds in the whole weak disorder phase, except possibly for the critical value itself.

2023/11/24

Algebraic Geometry Seminar

14:00-15:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Haidong Liu (Sun Yat-sen University)
On Kawamata-Miyaoka type inequality
[ Abstract ]
For klt projective varieties with nef and big canonical divisors, there exists a Miyaoka-Yau type inequality concerning the first and the second Chern classes. In this talk, I will present a Kawamata-Miyaoka type inequality for terminal Q-Fano varieties, which is a mirror version of the Miyaoka-Yau type inequality. This is a joint work with Jie Liu.

FJ-LMI Seminar

14:00-14:40   Room #117 (Graduate School of Math. Sci. Bldg.)
Gwénaël MASSUYEAU (Université de Bourgogne & CNRS)
Surgery equivalence relations on 3-manifolds (English)
[ Abstract ]
By some classical results in low-dimensional topology, any two 3-manifolds (with the “same” boundaries) are related one to the other by surgery operations. In this survey talk, we shall review this basic fact and, next, by restricting the type of surgeries, we shall consider several families of non-trivial equivalence relations on the set of (homeomorphism classes of) 3-manifolds. Those “surgery equivalence relations” are defined in terms of filtrations of the mapping class groups of surfaces, and their characterization / classification involves the notion of “finite-type invariant” which arises in quantum topology.
[ Reference URL ]
https://fj-lmi.cnrs.fr/seminars/

2023/11/22

Number Theory Seminar

17:00-18:00   Room #117 (Graduate School of Math. Sci. Bldg.)
Takao Yamazaki (Chuo University)
Torsion birational motives of surfaces and unramified cohomology (Japanese)

2023/11/21

Tuesday Seminar on Topology

17:30-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Yuya Koda (Keio University)
Shadows, divides and hyperbolic volumes (JAPANESE)
[ Abstract ]
In 2008, Costantino and D.Thurston revealed that the combinatorial structure of the Stein factorizations of stable maps from 3-manifolds into the real plane can be used to describe the hyperbolic structures of the complement of the set of definite fold points, which is a link. The key was that the Stein factorizations can naturally be embedded into 4-manifolds, and nice ideal polyhedral decompositions become visible on their boundaries. In this talk, we consider divides, which are the images of a proper and generic immersions of compact 1-manifolds into the 2-disk. Due to A'Campo's theory, each divide is associated with a link in the 3-sphere. By embedding a polyhedron induced from a given divide into the 4-ball as was done to Stein factorization, we can read off the ideal polyhedral decompositions on the boundary. We then show that the complement of the link of the divide can be obtained by Dehn filling a hyperbolic 3-manifold that admits a decomposition into several ideal regular hyperbolic polyhedra, where the number of each polyhedron is determined by types of the double points of the divide. This immediately gives an upper bound of the hyperbolic volume of the links of divides, which is shown to be asymptotically sharp. As in the case of Stein factorizations, an idea from the theory of Turaev's shadows plays an important role here. This talk is based on joint work with Ryoga Furutani (Hiroshima University).
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Operator Algebra Seminars

16:45-18:15   Room #128 (Graduate School of Math. Sci. Bldg.)
Mao Hoshino (Univ. Tokyo)
Finite index quantum subgroups of DQGs
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2023/11/20

Tokyo Probability Seminar

17:00-18:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Jun Kigami (Kyoto University)
Yet another construction of “Sobolev” spaces on metric spaces (日本語)

2023/11/16

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Takuya Yamauchi (Tohoku Univ.)
Isogeny graphs on superspecial abelian varieties: Eigenvalues, Connection to Bruhat-Tits buildings, and Property (T) (Japanese)
[ Abstract ]
For each fixed integer $g\ge 2$,  a prime $p$, and all primes $\ell$  with $\ell\neq p$, we can consider finite regular directed graphs associated with the set of equivalence classes of $\ell$-marked principally polarized superspecial abelian varieties of dimension $g$ in characteristic $p$. In this talk, I will explain that we can study such graphs in terms of the corresponding Bruhat-Tits buildings. I also discuss the eigenvalues values of the random walk matrices in view of the theory of automorphic representations when $g=2$. This is a joint work with Y. Aikawa (Tokyo university) and R. Tanaka (Kyoto university).  

2023/11/14

Tuesday Seminar on Topology

17:00-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Tomoo Yokoyama (Saitama University)
Dependency of the positive and negative long-time behaviors of flows on surfaces (JAPANESE)
[ Abstract ]
We discuss the dependence of a flow's positive and negative limit behaviors on a surface. In particular, I introduce the list of possible pairs of positive and negative limit behaviors that can and cannot occur. The idea of the dependence mechanism is illustrated using the dependence of the limit behavior of a toy model, a circle homeomorphism. We overview with as few prior knowledge assumptions as possible.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Numerical Analysis Seminar

16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Ken Furukawa (RIKEN)
On some dynamical systems and their prediction using data assimilation (Japanese)
[ Reference URL ]
ハイブリッド開催です。参加の詳細は参考URLをご覧ください。

Tuesday Seminar of Analysis

16:15-17:15   Room #126 (Graduate School of Math. Sci. Bldg.)
Arne Jensen (Aalborg University)
Resolvent expansions for magnetic Schrödinger operators (English)
[ Abstract ]
I will present some new results resolvent expansions around threshold zero for magnetic Schrödinger operators in dimension three. The magnetic field and the electric potential are assumed to decay sufficiently fast. Analogous results for Pauli operators will also be presented.
Joint work with H. Kovarik, Brescia, Italy.
[ Reference URL ]
https://forms.gle/qyEUeo4kVuPL1s289

Operator Algebra Seminars

16:45-18:15   Room #128 (Graduate School of Math. Sci. Bldg.)
Michiya Mori (Univ. Tokyo)
On the Scottish Book Problem 155 by Mazur and Sternbach
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2023/11/09

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Katsuyuki Takashima (Waseda Univ.)
Mathematical Aspects of Isogeny-Based Cryptography (Japanese)
[ Abstract ]
I will explain mathematical aspects of isogeny-based cryptography.

2023/11/07

Operator Algebra Seminars

16:45-18:15   Room #128 (Graduate School of Math. Sci. Bldg.)
Masato Tanaka (Nagoya Univ.)
A quantum analogue of the special linear group and its proper cocycle
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Tuesday Seminar on Topology

17:00-18:30   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Pre-registration required. See our seminar webpage.
Florent Schaffhauser (Heidelberg University)
Hodge numbers of moduli spaces of principal bundles on curves (ENGLISH)
[ Abstract ]
The Poincaré series of moduli stacks of semistable G-bundles on curves has been computed by Laumon and Rapoport. In this joint work with Melissa Liu, we show that the Hodge-Poincaré series of these moduli stacks can be computed in a similar way. As an application, we obtain a new proof of a joint result of the speaker with Erwan Brugallé, on the maximality on moduli spaces of vector bundles over real algebraic curves.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2023/11/02

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Masaya Yasuda (Rikkyo Univ.)
Algorithms for solving lattice problems and their applications (Japanese)
[ Abstract ]
In this talk, I introduce lattice algorithms such as LLL and BKZ reduction algorithms,
which are mandatory for solving lattice problems. I also describe how to solve LWE and
NTRU problems using lattice algorithms. In addition, I describe an application of lattice
algorithms for solving the integer factorization problem.

2023/11/01

Number Theory Seminar

17:00-18:00   Room #117 (Graduate School of Math. Sci. Bldg.)
Alex Youcis (University of Tokyo)
Prismatic realization functor for Shimura varieties of abelian type (English)
[ Abstract ]
Shimura varieties are certain classes of schemes which play an important role in various studies of number theory. The Langlands program is one of such examples. While far from known in general, it is expected that Shimura varieties are moduli spaces of certain motives with extra structure. In this talk I discuss joint work with Naoki Imai and Hiroki Kato, which constructs prismatic objects on the integral canonical models of Shimura varieties of abelian type at hyperspecial level. These may be thought of as the prismatic realization of such a hypothetical universal motive. I will also discuss how one can use this object to characterize these integral models, even at finite level.

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