Seminar information archive

Seminar information archive ~05/28Today's seminar 05/29 | Future seminars 05/30~

2020/07/30

thesis presentations

10:30-11:45   Online
LIN Dexie (Graduate Scool of Mathematical Sciences University of tokyo)
Monopole Floer homology for codimension-3 Riemannian foliation
[ Reference URL ]
https://forms.gle/jfh9Hpyt3XZXXcft6

2020/07/28

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Anderson Vera (RIMS, Kyoto University)
A double filtration for the mapping class group and the Goeritz group of the sphere (ENGLISH)
[ Abstract ]
I will talk about a double-indexed filtration of the mapping class group and of the Goeritz group of the sphere, the latter is the group of isotopy classes of self-homeomorphisms of the 3-sphere which preserves the standard Heegaard splitting of $S^3$. In particular I will explain how this double filtration allows to write the Torelli group as a product of some subgroups of the mapping class group. A similar study could be done for the group of automorphisms of a free group. (work in progress with K. Habiro)
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

thesis presentations

10:30-11:45   Online
Brkin,Sergei Vladimirovich (Graduate Scool of Mathematical Sciences University of tokyo)
Twisted arrow categories of operads and Segal conditions
[ Reference URL ]
https://forms.gle/jfh9Hpyt3XZXXcft6

2020/07/21

Numerical Analysis Seminar

16:30-18:00   Online
Tomoya Kemmochi (Nagoya University)
Structure-preserving numerical schemes for constrained gradient flows of planar curves (Japanese)
[ Reference URL ]
https://forms.gle/3JiNEjWnrWLW8cFA9

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Sergei Burkin (The University of Tokyo)
Twisted arrow categories of operads and Segal conditions (ENGLISH)
[ Abstract ]
We generalize twisted arrow category construction from categories to operads, and show that several important categories, including the simplex category $\Delta$, Segal's category $\Gamma$ and Moerdijk--Weiss category $\Omega$ are twisted arrow categories of operads. Twisted arrow categories of operads are closely connected with Segal conditions, and the corresponding theory can be generalized from multi-object associative algebras (i.e. categories) to multi-object P-algebras for reasonably nice operads P.
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

Tuesday Seminar on Topology

18:00-19:00   Online
Pre-registration required. See our seminar webpage.
Dexie Lin (The University of Tokyo)
Monopole Floer homology for codimension-3 Riemannian foliation (ENGLISH)
[ Abstract ]
In this paper, we give a systematic study of Seiberg-Witten theory on closed oriented manifold with codimension-3 oriented Riemannian foliation. Under a certain topological condition, we construct the basic monopole Floer homologies for a transverse spinc structure with a bundle-like metric, generic perturbation and a complete local system. We will show that these homologies are independent of the bundle-like metric and generic perturbation. The major difference between the basic monopole Floer homologies and the ones on manifolds is the necessity to use the complete local system to construct the monopole Floer homologies.
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

2020/07/16

Operator Algebra Seminars

16:45-18:15   Online
Christian Voigt (Univ. Glasgow)
Complex quantum groups and the Baum-Connes conjecture (English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Information Mathematics Seminar

16:50-18:35   Online
HIroshi Fujiwara (BroadBand Tower, Inc.)
Basics of the speedup technique of the classic computing and Innovation of Causality in the root of the quantum computing (Japanese)
[ Abstract ]
Explanation of the speedup technique of the classic computing and innovation of causality in the root of the quantum computing
[ Reference URL ]
[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

2020/07/14

Tuesday Seminar on Topology

17:30-18:30   Online
Joint with Lie Groups and Representation Theory Seminar. Pre-registration required. See our seminar webpage.
Takayuki Okuda (Hiroshima University)
Kobayashi's properness criterion and totally geodesic submanifolds in locally symmetric spaces (JAPANESE)
[ Abstract ]
Let G be a Lie group and X a homogeneous G-space. A discrete subgroup of G acting on X properly is called a discontinuous group for X. We are interested in constructions and classifications of discontinuous groups for a given X.

It is well-known that if the isotropies of G on X are compact, any closed subgroup acts on X properly. However, the cases where the isotropies are non-compact, the same claim does not hold in general.

Let us consider the case where G is a linear reductive. In this situation, T. Kobayashi [Math. Ann. (1989)], [J. Lie Theory (1996)]
gave a criterion for the properness of the action on a homogeneous G-space X of closed subgroups in G.

In this talk, we consider homogeneous G-spaces of reductive types realized as families of totally geodesic submanifolds in non-compact Riemannian symmetric spaces. As a main result, we give a translation of Kobayashi's criterion within the framework of Riemannian geometry. In particular, for a torsion-free discrete subgroup of G, the criterion can be stated in terms of totally geodesic submanifolds in the Riemannian locally symmetric space corresponding to the subgroup in G.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Lie Groups and Representation Theory

17:30-18:30   Room ## (Graduate School of Math. Sci. Bldg.)
Joint with Tuesday Seminar on Topology. Online.
Takayuki Okuda (Hiroshima University)
Kobayashi's properness criterion and totally geodesic submanifolds in locally symmetric spaces (Japanese)
[ Abstract ]
Let G be a Lie group and X a homogeneous G-space.
A discrete subgroup of G acting on X properly is called a discontinuous group for X.
We are interested in constructions and classifications of discontinuous groups for a given X.

It is well-known that if the isotropies of G on X are compact, any closed subgroup acts on X properly.
However, the cases where the isotropies are non-compact, the same claim does not hold in general.

Let us consider the case where G is a linear reductive.
In this situation, T. Kobayashi [Math. Ann. (1989)], [J. Lie Theory (1996)] gave a criterion for the properness of the action on a homogeneous G-space X of closed subgroups in G.

In this talk, we consider homogeneous G-spaces of reductive types realized as families of totally geodesic submanifolds in non-compact Riemannian symmetric spaces.
As a main result, we give a translation of Kobayashi's criterion within the framework of Riemannian geometry.
In particular, for a torsion-free discrete subgroup of G, the criterion can be stated in terms of totally geodesic submanifolds in the Riemannian locally symmetric space corresponding to the subgroup in G.

2020/07/13

Seminar on Geometric Complex Analysis

10:30-12:00   Online
INOUE Eiji (University of Tokyo)
$\mu$-cscK metrics and $\mu$K-stability of polarized manifolds
[ Reference URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

2020/07/09

Operator Algebra Seminars

16:45-18:15   Online
Amine Marrakchi (ENS Lyon)
Affine isometric actions of groups on $L_p$-spaces : dependence on the value of $p$ (English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Information Mathematics Seminar

16:50-18:35   Online
Hiroshi Fujiwara (BroadBand Tower, Inc.)
Ways from machine learning to deep learning (Japanese)
[ Abstract ]
Explanation of ways from machine learning to deep learning
[ Reference URL ]
[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

2020/07/07

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Yuta Nozaki (Hiroshima University)
Abelian quotients of the Y-filtration on the homology cylinders via the LMO functor (JAPANESE)
[ Abstract ]
We construct a series of homomorphisms on the Y-filtration on the homology cylinders via the mod $\mathbb{Z}$ reduction of the LMO functor. The restriction of our homomorphism to the lower central series of the Torelli group does not factor through Morita's refinement of the Johnson homomorphism. We use it to show that the abelianization of the Johnson kernel of a closed surface has torsion elements. This is the joint work with Masatoshi Sato and Masaaki Suzuki.
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

2020/07/06

Seminar on Geometric Complex Analysis

10:30-12:00   Online
INAYAMA Takahiro (University of Tokyo)
Nakano positivity of singular Hermitian metrics and vanishing theorems of Demailly-Nadel-Nakano type (Japanese?)
[ Abstract ]
We propose a general definition of Nakano semi-positivity of singular Hermitian metrics on holomorphic vector bundles. By using this positivity notion, we establish $L^2$-estimates for holomorphic vector bundles with Nakano positive singular Hermitian metrics. We also show vanishing theorems, which generalize both Nakano type and Demailly-Nadel type vanishing theorems.
[ Reference URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

2020/07/02

Operator Algebra Seminars

16:45-18:15   Online
Toshihiko Masuda (Kyushu Univ.)
Outer actions ($\mathcal{G}$-kernels) of discrete amenable groupoids on injective factors (English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Information Mathematics Seminar

16:50-18:35   Online
Hiroshi Fujiwara (BroadBand Tower, Inc.)
Telework society and menace of the cyber attack (Japanese)
[ Abstract ]
Explanation on the menace of the cyber attack in telework society.
[ Reference URL ]
[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

2020/06/30

Numerical Analysis Seminar

16:30-18:00   Online
Koya Sakakibara (Okayama University of Science)
Structure-preserving numerical methods for interface problems (Japanese)
[ Reference URL ]
https://forms.gle/ztK741vNdBT7hfGSA

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Daniel Matei (IMAR Bucharest)
Homology of right-angled Artin kernels (ENGLISH)
[ Abstract ]
The right-angled Artin groups A(G) are the finitely presented groups associated to a finite simplicial graph G=(V,E), which are generated by the vertices V satisfying commutator relations vw=wv for every edge vw in E. An Artin kernel
Nh(G) is defined by an epimorphism h of A(G) onto the integers. In this talk, we discuss the module structure over the Laurent polynomial ring of the homology groups of Nh(G).
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

2020/06/29

Seminar on Geometric Complex Analysis

10:30-12:00   Online
KUSAKABE Yuta (Osaka University)
Oka properties of complements of holomorphically convex sets

[ Abstract ]
A complex manifold is called an Oka manifold if the Oka principle for maps from Stein spaces holds. In this talk, we consider the question of when a holomorphically convex set in an Oka manifold has an Oka complement. Our main theorem states that the complement of a compact holomorphically convex set in a Stein manifold with the density property is an Oka manifold.
This gives a positive answer to the well-known long-standing problem in Oka theory whether the complement of a compact polynomially convex set in $\mathbb{C}^{n}$ $(n>1)$ is Oka. The relative version of the main theorem can also be proved.
As an application, we show that the complement $\mathbb{C}^{n}\setminus\mathbb{R}^{k}$ of a totally real affine subspace is Oka if $n>1$ and $(n,k)\neq(2,1),(2,2),(3,3)$.
[ Reference URL ]
https://forms.gle/vSFPoVR6ugrkTGhX7

2020/06/25

Operator Algebra Seminars

16:45-18:15   Online
Remi Boutonnet (Univ. Bordeaux)
Properly proximal groups and their von Neumann algebras (English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2020/06/24

Discrete mathematical modelling seminar

15:00-16:30   Online
The seminar will be held using Zoom. If you wish to participate, please contact R. Willox by email.
Martin Skrodzki (RIKEN iTHEMS)
Combinatorial and Asymptotical Results on the Neighborhood Grid Data Structure (English)
[ Abstract ]
In 2009, Joselli et al. introduced the Neighborhood Grid data structure for fast computation of neighborhood estimates in point clouds. Even though the data structure has been used in several applications and shown to be practically relevant, it is theoretically not yet well understood. The purpose of this talk is to present a polynomial-time algorithm to build the data structure. Furthermore, we establish the presented algorithm to be time-optimal. This investigations leads to several combinatorial questions for which partial results are given.

2020/06/23

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Hokuto Konno (The University of Tokyo)
Gauge theory and the diffeomorphism and homeomorphism groups of 4-manifolds (JAPANESE)
[ Abstract ]
I will explain my recent collaboration with several groups that develops gauge theory for families
to extract difference between the diffeomorphism groups and the homeomorphism groups of 4-manifolds.
After Donaldson’s celebrated diagonalization theorem, gauge theory has given strong constraints on the topology of smooth 4-manifolds. Combining such constraints with Freedman’s theory, one may find many non-smoothable topological 4-manifolds.
Recently, a family version of this argument was started by T. Kato, N. Nakamura and myself, and soon later it was developed also by D. Baraglia and his collaborating work with myself. More precisely, considering gauge theory for smooth fiber bundles of 4-manifolds, they obtained some constraints on the topology of smooth 4-manifold bundles. Using such constraints, they detected non-smoothable topological fiber bundles of smooth 4-manifolds. The existence of such bundles implies that there is homotopical difference between the diffeomorphism and homeomorphism groups of the 4-manifolds given as the fibers.
If time permits, I will also mention my collaboration with Baraglia which shows that a K3 surface gives a counterexample to the Nielsen realization problem in dimension 4. This example reveals also that there is difference between the Nielsen realization problems asked in the smooth category and the topological category.
[ Reference URL ]
https://zoom.us/webinar/register/WN_oS594Z6BRyaKNCvlm3yCoQ

Numerical Analysis Seminar

16:30-18:00   Online
Shun Sato (The University of Tokyo)
Linearly implicit and high-order conservative schemes for ordinary differential equations with a quadratic invariant (Japanese)
[ Reference URL ]
https://forms.gle/hvvvFLAhH1314UQK8

2020/06/18

Information Mathematics Seminar

16:50-18:35   Online
Hiroshi Fujiwara (BroadBand Tower, Inc.)
Ways from speedup of the classic computing to a quantum (Japanese)
[ Abstract ]
Explanation of ways from speedup of the classic computing to a quantum
[ Reference URL ]
[学外用] https://docs.google.com/forms/d/1d1RWvV8j1TzXg8eF93zMZeIzJeIvdq9zY8htO8w2St0/ [学内用] https://bit.ly/2zCBj8x (g.ecc.u-tokyo.ac.jpアカウントでアクセスできます)

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