Seminar information archive

Seminar on Probability and Statistics

14:30-16:00   Room # (Graduate School of Math. Sci. Bldg.)
Martin Hazelton (Otago University)
Dynamic fibre samplers for linear inverse problems
[ Abstract ]
Asia-Pacific Seminar in Probability and Statistics (APSPS)

Statistical inverse problems occur when we wish to learn about some random process that is observed only indirectly. Inference in such situations typically involves sampling possible values for the latent variables of interest conditional on the indirect observations. For count data, the latent variables are constrained to lie on a fibre (solution set for the linear system) comprising the integer lattice within a convex polytope.

Sampling the latent counts can be conducted using MCMC methods,through a random walk on this fibre. A major challenge is finding a set of basic moves that ensures connectedness of the walk over the fibre. In principle this can be done by computing a Markov basis of potential moves, but the resulting sampler can be hugely inefficient even when such a basis is computable. In this talk I will describe some current work on developing a dynamic Markov basis that generates moves on the fly. This approach can guarantee irreducibility of the sampler while gaining efficiency by increasing the probability of selecting serviceable sampling directions.
[ Reference URL ]

2022/01/18

Operator Algebra Seminars

16:45-18:15   Online
Miho Mukohara (Univ. Tokyo)
C$^*$-simplicity of relative profinite completions of generalized Baumslag-Solitar groups

[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Tokyo-Nagoya Algebra Seminar

15:00-16:30   Online
Please see the URL below for details on the online seminar.
Haruhisa Enomoto (Osaka Prefecture University)
Exact-categorical properties of subcategories of abelian categories 1 (Japanese)
[ Abstract ]
Quillen's exact category is a powerful framework for studying extension-closed subcategories of abelian categories, and provides many interesting questions on such subcategories.
In the first talk, I will explain the basics of some properties and invariants of exact categories (e.g. the Jordan-Holder property, simple objects, and Grothendieck monoid).
In the second talk, I will give some results and questions about particular classes of exact categories arising in the representation theory of algebras (e.g. torsion(-free) classes over path algebras and preprojective algebras).
If time permits, I will discuss questions of whether these results can be generalized to extriangulated categories (extension-closed subcategories of triangulated categories).
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Lie Groups and Representation Theory

17:00-18:00   Room #On line (Graduate School of Math. Sci. Bldg.)
Hideyuki Ishi (Osaka City University)
Strongly visible actions on complex domains (Japanese)
[ Abstract ]
In this century, the Cartan-Hartogs domain and its variations, on which the Bergman kernel function and the Kahler-Einstein metric can be computed explicitly, have been actively studied. Reasoning that strongly visible actions on the domains enable such nice calculations, we introduce a new type of complex domain analogous to the Cartan-Hartogs domain, and present a research plan about harmonic analysis over the domain.

2022/01/13

Information Mathematics Seminar

16:50-18:35   Online
Keita Xagawa (NTT)
Lattice-based cryptography and its applications (Japanese)
[ Abstract ]
Explanation on lattice-based cryptography and its applications
[ Reference URL ]

2022/01/11

Operator Algebra Seminars

16:45-18:15   Online
Akihiro Miyagawa (Kyoto University)
Rationality for operators in free semicircular elements
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Tuesday Seminar on Topology

17:00-18:00   Online
Joint with Lie Groups and Representation Theory Seminar. See our seminar webpage.
Keiichi Maeta (The Univesity of Tokyo)
On the existence problem of Compact Clifford-Klein forms of indecomposable pseudo-Riemannian symmetric spaces with signature (n,2) (JAPANESE)
[ Abstract ]
For a homogeneous space $G/H$ and its discontinuous group $\Gamma\subset G$, the double coset space $\Gamma\backslash G/H$ is called a Clifford-Klein form of $G/H$. In the study of Clifford-Klein forms, the classification of homogeneous spaces which admit compact Clifford—Klein forms is one of the important open problems, which was introduced by Toshiyuki Kobayashi in 1980s. We consider this problem for indecomposable and reducible pseudo-Riemannian symmetric spaces with signature (n,2). We show the non-existence of compact Clifford-Klein forms for some series of symmetric spaces, and construct new compact Clifford-Klein forms of countably infinite five-dimensional pseudo-Riemannian symmetric spaces with signature (3,2).
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Lie Groups and Representation Theory

17:00-18:00   Room #on line (Graduate School of Math. Sci. Bldg.)
Joint with Tuesday Seminar on Topology.
Keiichi Maeta (The University of Tokyo)
On the existence problem of Compact Clifford-Klein forms of indecomposable pseudo-Riemannian symmetric spaces with signature (n,2) (Japanese)
[ Abstract ]
For a homogeneous space $G/H$ and its discontinuous group $\Gamma\subset G$, the double coset space $\Gamma\backslash G/H$ is called a Clifford-Klein form of $G/H$. In the study of Clifford-Klein forms, the classification of homogeneous spaces which admit compact Clifford-Klein forms is one of the important open problems, which was introduced by Toshiyuki Kobayashi in 1980s.

We consider this problem for indecomposable and reducible pseudo-Riemannian symmetric spaces with signature (n,2). We show the non-existence of compact Clifford-Klein forms for some series of symmetric spaces, and construct new compact Clifford-Klein forms of countably infinite five-dimensional pseudo-Riemannian symmetric spaces with signature (3,2).

2022/01/06

Information Mathematics Seminar

16:50-18:35   Online
Next cyber security strategy of the Japanese Government (Japanese)
[ Abstract ]
Explanation on next cyber security strategy of the Japanese government
[ Reference URL ]

2021/12/23

Information Mathematics Seminar

16:50-18:35   Online
The cyber attack to the Ministry of Defense-affiliated company and zero trust of Amazon/Google (Japanese)
[ Abstract ]
Explanation on the cyber attack to the Ministry of Defense-affiliated company and zero trust of Amazon/Google
[ Reference URL ]

2021/12/22

Number Theory Seminar

17:00-18:00   Online
Stefano Morra (Paris 8 University)
Some properties of the Hecke eigenclasses of the mod p-cohomology of Shimura curves (English)
[ Abstract ]
The mod p local Langlands program, foreseen by Serre and proposed in precise terms by C. Breuil after his p-divisible groups computations in the Breuil-Conrad-Diamond-Taylor proof of the Shimura-Taiyama-Weil conjecture, was realized in the particular case of GL_2(\mathbf{Q}_p) thanks to a vast convergence of new tools: classification of mod p-representations of GL_2(\mathbf{Q}_p), local Galois deformation techniques, local-global compatibility arguments.
When trying to extend these conjectures to more general groups, multiple problems arise (lack of classification results for smooth mod p-representations of p-adic groups, absence of explicit integral models for Galois representations with the relevant p-adic Hodge theory conditions), and the only way to formulate, and test, conjectures on a mod p local Langlands correspondence relies on its expected realization in Hecke eigenclasses of Shimura varieties (or, in other words, the expectation of a local-global compatibility of the Langlands correspondence).
In this talk we describe some properties of Hecke isotypical spaces of the mod p-cohomology of Shimura curves with infinite level at p, when the reflex field F is unramified at p and the Shimura curve arises from a quaternion algebra which is split at p. These Hecke isotypical spaces are expected to be the “good” smooth mod p-representations of GL_2(F_{\mathfrak{p}}) attached to mod p Galois representations of Gal(\overline{\mathbf{Q}_p}/F_{\mathfrak{p}}) via the expected local Langlands correspondence mod p. We will in particular comment on their Gelfand-Kirillov dimension, and their irreducibility (in particular, the finite length of these Hecke eigenspaces as GL_2(F_{\mathfrak{p}})-representations).
This is a report on a series of work joint with C. Breuil, F. Herzig, Y. Hu et B. Schraen.

2021/12/21

Tuesday Seminar on Topology

17:30-18:30   Online
Joint with Lie Groups and Representation Theory Seminar. See our seminar webpage.
Hiroki Shimakura (Tohoku University)
Classification of holomorphic vertex operator algebras of central charge 24 (JAPANESE)
[ Abstract ]
Holomorphic vertex operator algebras are imporant in vertex operator algebra theory. For example, the famous moonshine vertex operator algebra is holomorphic. One of the fundamental problems is to classify holomorphic vertex operator algebras. It is known that holomorphic vertex operator algebras of central charge 8 and 16 are lattice vertex operator algebras. I will talk about recent progress on the classification of holomorphic vertex operator algebras of central charge 24.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Operator Algebra Seminars

16:45-18:15   Online
Wojciech Dybalski (Adam Mickiewicz University in Poznan)
Interacting massless infraparticles in 1+1 dimensions
(English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Lie Groups and Representation Theory

17:30-18:30   Room #on line (Graduate School of Math. Sci. Bldg.)
Joint with Tuesday Seminar on Topology.
Hiroki Shimakura (Tohoku University)
Classification of holomorphic vertex operator algebras of central charge 24
(Japanese)
[ Abstract ]
Holomorphic vertex operator algebras are important in vertex operator algebra theory. For example, the famous moonshine vertex operator algebra is holomorphic.
One of the fundamental problems is to classify holomorphic vertex operator algebras. It is known that holomorphic vertex operator algebras of central charge 8 and 16 are lattice vertex operator algebras.
I will talk about recent progress on the classification of holomorphic vertex operator algebras of central charge 24.

2021/12/17

Colloquium

15:30-16:30   Online
Registration is closed (12:00, December 17).
Jun-Muk Hwang (Center for Complex Geometry, IBS, Korea)
Growth vectors of distributions and lines on projective hypersurfaces (ENGLISH)
[ Abstract ]
For a distribution on a manifold, its growth vector is a finite sequence of integers measuring the dimensions of the directions spanned by successive Lie brackets of local vector fields belonging to the distribution. The growth vector is the most basic invariant of a distribution, but it is sometimes hard to compute. As an example, we discuss natural distributions on the spaces of lines covering hypersurfaces of low degrees in the complex projective space. We explain the ideas in a joint work with Qifeng Li where the growth vector is determined for lines on a general hypersurface of degree 4 and dimension 5.

2021/12/16

Applied Analysis

16:00-17:00   Online
Zhanpeisov Erbol ( )
Existence of solutions for fractional semilinear parabolic equations in Besov-Morrey spaces (Japanese)
[ Reference URL ]
https://forms.gle/whpkgAwYvyQKQMzM8

Tokyo-Nagoya Algebra Seminar

16:45-18:15   Online
Please see the URL below for details on the online seminar.
Nicholas Williams (University of Cologne)
Cyclic polytopes and higher Auslander-Reiten theory (English)
[ Abstract ]
Oppermann and Thomas show that tilting modules over Iyama’s higher Auslander algebras of type A are in bijection with triangulations of even-dimensional cyclic polytopes. Triangulations of cyclic polytopes are partially ordered in two natural ways known as the higher Stasheff-Tamari orders, which were introduced in the 1990s by Kapranov, Voevodsky, Edelman, and Reiner as higher-dimensional generalisations of the Tamari lattice. These two partial orders were conjectured to be equal in 1996 by Edelman and Reiner, and we prove that this conjecture is true. We further show how the higher Stasheff-Tamari orders correspond in even dimensions to natural orders on tilting modules which were studied by Riedtmann, Schofield, Happel, and Unger. This then allows us to complete the picture of Oppermann and Thomas by showing that triangulations of odd-dimensional cyclic polytopes correspond to equivalence classes of d-maximal green sequences, which we introduce as higher-dimensional analogues of Keller’s maximal green sequences. We show that the higher Stasheff-Tamari orders correspond to natural orders on equivalence classes of d-maximal green sequences, which relate to the no-gap conjecture of Brustle, Dupont, and Perotin. The equality of the higher Stasheff-Tamari orders then implies that these algebraic orders on tilting modules and d-maximal green sequences are equal. If time permits, we will also discuss some results on mutation of cluster-tilting objects and triangulations.
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Information Mathematics Seminar

16:50-18:35   Online
The cyber attack to a car company supply chain network and Zero trust by the Cisco Systems (Japanese)
[ Abstract ]
Explanation on the cyber attack to the supply chain network of car company and zero trust by the Cisco Systems
[ Reference URL ]

2021/12/15

Seminar on Probability and Statistics

14:30-16:00   Room # (Graduate School of Math. Sci. Bldg.)
Estate Khmaladze (Victoria University of Wellington)
Theory of Distribution-free Testing
[ Abstract ]
Asia-Pacific Seminar in Probability and Statistics (APSPS)

The aim of the talk is to introduce transformations of empirical-type processes by a group of unitary operators. Recall that if v_{nP} is empirical process on real line, based on a sample from P, it can be mapped into empirical process v_{nQ} by appropriate change of time

v_{nP}(h(x))=v_{nQ}(x)

where h(x) is continuous and increasing. This is the basis for distribution-free theory of goodness of fit testing. If w(\phi) is a function-parametric “empirical-type” process (i.e. has functions \phi from a space L as a time) and if K* is a unitary operator on L, then transformed process Kw we define as
Kw(\phi) = w(K*\phi)

These two formulas have good similarity, but one transformation in on the real line, while the other transformation in on functional space.This later one turns out to be of very broad use, and allows to base distribution-free theory upon it. Examples, we have specific results for, are parametric empirical
processes in R^d, regression empirical processes, those in GLM, parametric models for point processes and for Markov processes in discrete time. Hopefully, further examples will follow.
[ Reference URL ]

2021/12/14

Operator Algebra Seminars

16:45-18:15   Online
Karen Strung (Czech Academy of Science)
Constructions in minimal amenable dynamics and applications to classification of $C^*$-algebras

[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Lie Groups and Representation Theory

17:00-18:00   Room #on line (Graduate School of Math. Sci. Bldg.)
Yosuke Morita (Kyoto University)
On the definition of Conley indices (Japanese)
[ Abstract ]
Conley indices are used to describe local behaviour of topological dynamical systems. In this talk, I will explain a new framework for Conley index theory. Our approach is very elementary, and uses only general topology and some computations of inclusion relations of subsets.

2021/12/13

Seminar on Geometric Complex Analysis

10:30-12:00   Online
Masaya Kawamura (National Institute of Technology)
A generalized Hermitian curvature flow on almost Hermitian manifolds (Japanese)
[ Abstract ]
It is well-known that the Uniformization theorem (any Riemannian metric on a closed 2-manifold is conformal to one of constant curvature) can be proven by using the Ricci flow. J. Streets and G. Tian questioned whether or not a geometric flow can be used to classify non-Kähler complex surfaces as in the case of the Ricci flow. Also they asked if it is possible to prove classification results in higher dimensions by using geometric flows in non-Kähler Hermitian geometry. Streets and Tian considered that these flows should be close to the Kähler-Ricci flow as much as possible. From this point of view, they introduced a geometric flow called the Hermitian curvature flow (HCF) which evolves an initial Hermitian metric in the direction of a Ricci-type tensor of the Chern connection modified with some lower order torsion terms. Streets and Tian also introduced another geometric flow, which is called the pluriclosed flow (PCF), by choosing torsion terms to preserve the pluriclosed condition on Hermitian metrics. Y. Ustinovskiy studied a particular version of the HCF over a compact Hermitian manifold. Ustinovskiy proved that if the initial metric has Griffiths positive (non-negative) Chern curvature, then this property is preserved along the flow.

In recent years, some results concerning geometric flows on complex manifolds have been extended to the almost complex setting. For instance, L. Vezzoni defined a new Hermitian curvature flow on almost Hermitian manifolds for generalizing some studies on the HCF and the Hermitian Hilbert functional. And J. Chu, V. Tosatti and B. Weinkove considered parabolic Monge-Ampère equation on almost Hermitian manifolds, which is equivalent to the almost complex Chern-Ricci flow. T. Zheng characterized the maximal existence time for a solution to the almost complex Chern-Ricci flow.

In this talk, we consider a generalized Hermitian curvature flow in almost Hermitian geometry and introduce that it has some properties such as the long-time existence obstruction, the uniform equivalence between its solution and an almost Hermitian metric, and the preservation result along the flow.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tJ0vcu2rrDIqG9Rv5AT0Mpi37urIkJ1IRldB

2021/12/09

Information Mathematics Seminar

16:50-18:35   Online
The consideration of the account injustice access case and zero trust by Microsoft (Japanese)
[ Abstract ]
The explanation on the account injustice access case and zero trust by Microsoft
[ Reference URL ]

2021/12/07

Operator Algebra Seminars

16:45-18:15   Online
Junichiro Matsuda (Kyoto Univ.)
Classification of quantum graphs on $M_2$ and their quantum automorphism groups
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Tuesday Seminar on Topology

17:00-1800   Online
Pre-registration required. See our seminar webpage.
Taketo Sano (The Univesity of Tokyo)
A Bar-Natan homotopy type (JAPANESE)
[ Abstract ]
In year 2000, Khovanov introduced a categorification of the Jones polynomial, now known as Khovanov homology. In 2014, Lipshitz and Sarkar introduced a spatial refinement of Khovanov homology, called Khovanov homotopy type, which is a finite CW spectrum whose reduced cellular cohomology recovers Khovanov homology. On the algebraic level, there are several deformations of Khovanov homology, such as Lee homology and Bar-Natan homology. These variants are also important in that they give knot invariants such as Rasmussen’s $s$-invariant. Whether these variants admit spatial refinements have been open.

In 2021, the speaker constructed a spatial refinement of Bar-Natan homology and determined its stable homotopy type. The construction follows that of Lipshitz and Sarkar, which is based on the construction proposed by Cohen, Segal and Jones using the concept of flow categories. Also, we adopt techniques called “Morse moves in flow categories” introduced by Lobb et.al. to determine the stable homotopy type. Spacialy (or homotopically) refining the $s$-invariant is left as a future work.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html