Seminar information archive

Seminar information archive ~03/28Today's seminar 03/29 | Future seminars 03/30~

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.
Mayuko Yamashita (Kyoto University)
Anderson self-duality of topological modular forms and heretoric string theory (JAPANESE)
[ Abstract ]
Topological Modular Forms (TMF) is an E-infinity ring spectrum which is conjectured by Stolz-Teichner to classify two-dimensional supersymmetric quantum field theories in physics. In the previous work with Y. Tachikawa, we proved the vanishing of anomalies in heterotic string theory mathematically by using TMF. In this talk, I explain our recent update on the previous work. Because of the vanishing result, we can consider a secondary transformation of spectra, which is shown to coincide with the Anderson self-duality morphism of TMF. This allows us to detect subtle torsion phenomena in TMF by differential-geometric ways.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

Tokyo-Nagoya Algebra Seminar

15:00-16:30   Online
Antoine de Saint Germain (University of Hong Kong)
Cluster-additive functions and frieze patterns with coefficients (English)
[ Abstract ]
In his study of combinatorial features of cluster categories and cluster-tilted algebras, Ringel introduced an analogue of additive functions of stable translation quivers called cluster-additive functions.

In the first part of this talk, we will define cluster-additive functions associated to any acyclic mutation matrix, relate them to mutations of the cluster X variety, and realise their values as certain compatibility degrees between functions on the cluster A variety associated to the Langlands dual mutation matrix (in accordance with the philosophy of Fock-Goncharov). This is based on joint work with Peigen Cao and Jiang-Hua Lu. In the second part of this talk, we will introduce the notion of frieze patterns with coefficients based on joint work with Min Huang and Jiang-Hua Lu. We will then discuss their connection with cluster-additive functions.

ミーティングID: 815 4247 1556
パスコード: 742240
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Lie Groups and Representation Theory

17:00-18:00   Room #online (Graduate School of Math. Sci. Bldg.)
Hiroyoshi TAMORI (Shibaura institute of technology)
Integral expression of the $(k,a)$-generalized Laguerre semigroup
(Japanese)
[ Abstract ]
The $(k,a)$-generalized Laguerre semigroup was introduced by Ben
Sa\"{\i}d--Kobayashi-{\O}rsted as an interpolation of the Hermite semigroup (the k=0, a=2 case) and the Laguerre semigroup (the k=0, a=1 case). Based on a joint work with Kouichi Taira (Ritsumeikan University), I will explain an integral expression of the semigroup and an upper estimate of the integral kernel, which leads to Strichartz estimates for operators $|x|^{2-a}\Delta_{k}-|x|^a$ and $|x|^{2-a}\Delta_{k}$ ($\Delta_k$ denotes the Dunkl Laplacian) under some condition on the deformation parameter $(k,a)$.

2023/05/15

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Yuya Takeuchi (Tsukuba Univeristy)
$\mathcal{I}'$-curvatures and the Hirachi conjecture (Japanese)
[ Abstract ]
Hirachi conjecture deals with a relation between the integrals of local pseudo-Hermitian invariants and global CR invariants. This is a CR analogue of the Deser-Schwimmer conjceture, which was proved by Alexakis. In this talk, I would like to explain some results on the Hirachi conjecture. In particular, I'll introduce the $\mathcal{I}'$-curvatures and prove that these produce counterexamples to the Hirachi conjecture in higher dimensions. This talk is based on joint work with Jeffrey S. Case.
[ 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.)
岡田いず海 (千葉大学)
Capacity of the range of random walk (JAPANESE)
[ Abstract ]
We study the capacity of the range of a simple random walk in three and higher dimensions. It is known that the order of the capacity of the random walk range in n dimensions is similar to that of the volume of the random walk range in n-2 dimensions. We show that this correspondence breaks down for the law of the iterated logarithm for the capacity of the random walk range in three dimensions. We also prove the law of the iterated logarithm in higher dimensions. This is joint work with Amir Dembo.

2023/05/11

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Tatsuaki Okamoto (NTT)
The security definition and proof of symmetric key encryption and public key encryption (Japanese)
[ Abstract ]
Explanation of the security definition and proof of symmetric key encryption and public key encryption

2023/05/10

Number Theory Seminar

17:00-18:00   Room #117 (Graduate School of Math. Sci. Bldg.)
Guy Henniart (Paris-Sud University)
Swan exponent of Galois representations and fonctoriality for classical groups over p-adic fields (English)
[ Abstract ]
This is joint work with Masao Oi in Kyoto. Let F be a p-adic field for some prime number p,
F^ac an algebraic closure of F, and G_F the Galois group of F^ac/F. A continuous finite dimensional
representation σ (on a complex vector space W) has a Swan exponent s(σ), a non-negative integer
which measures how "wildly ramified" σ is. Langlands functoriality makes it of interest
to compare s(σ) and s(r o σ) when r is an algebraic representation of Aut_C(W). The first cases
for r are the determinant, the adjoint representation, the symmetric square representation and
the alternating square representation. I shall give some relations (inequalities mostly, with
equality in interesting cases) between the Swan exponents of those representations r o σ. I shall
also indicate how such relations can be used to explicit the local Langlands correspondence of
Arthur for some simple cuspidal representations of split classical groups over F.

Algebraic Geometry Seminar

13:30-15:00   Room #ハイブリッド開催/056 (Graduate School of Math. Sci. Bldg.)
Jakub Witaszek (Princeton University)
Singularities in mixed characteristic via the Riemann-Hilbert correspondence (English)
[ Abstract ]
In my talk, I will start by reviewing how various properties of characteristic zero singularities can be understood topologically by ways of the Riemann-Hilbert correspondence. After that, I will explain how similar ideas can be applied in the study of mixed characteristic singularities. This is based on a joint work (in progress) with Bhargav Bhatt, Linquan Ma, Zsolt Patakfalvi, Karl Schwede, Kevin Tucker, and Joe Waldron.

2023/05/09

Operator Algebra Seminars

16:45-18:15   Room #126 (Graduate School of Math. Sci. Bldg.)
Yoh Tanimoto (Univ Rome, Tor Vergata)
Lattice Green functions (after Balaban/Dimock) (English)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Michihisa Wakui (Kansai University)
Knots and frieze patterns (JAPANESE)
[ Abstract ]
(joint work with Prof. Takeyoshi Kogiso (Josai University)) In the early 1970s, Conway and Coxeter introduced frieze patterns of positive integers arranged under the unimodular rule ad-bc=1, and showed that they are classified by triangulations of convex polygons. Currently, the frieze patterns by Conway and Coxeter are spotlighted in connection with cluster algebras which are introduced by Fomin and Zelevinsky in the early 2000s.

Working with Takeyoshi Kogiso in Josai University the speaker study on relationship between rational links and Conway-Coxeter friezes through ancestor triangles of rational numbers introduced by Shuji Yamada in Kyoto Sangyo University, and show that rational links are characterized by Conway-Coxeter friezes of zigzag type. At nearly the same time Morier-Genoud and Ovsienko also introduce the concept of q-deformation of rational numbers based on continued fraction expansions, and derive closely related results to our research. In this seminar we will talk about an outline of these results.
[ Reference URL ]
https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index_e.html

2023/05/08

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Hisashi Kasuya (Osaka Univeristy)
Non-Kähler Hodge theory and resolutions of cyclic orbifolds (日本語)
[ Abstract ]
This talk is based on the joint works with Jonas Stelzig (LMU München). We discuss the Hodge theory of non-Kähler compact complex manifolds. In this term, we think several types of compact complex manifolds and compact Kähler manifolds are considered as the "simplest”. We give a way of constructing simply connected compact complex non-Kähler manifolds of certain types by using resolutions of cyclic orbifolds.
[ 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.)
新井裕太 (千葉商科大学)
On the Chapman-Kolmogorov equation for LPP (JAPANESE)
[ Abstract ]
KPZ普遍クラスに属するいくつかのモデルにおいて,その推移確率等が複素積分形の関数で書き表せることが知られている.しかしながら,複素積分を用いた計算は複雑となることも多く,KPZ普遍クラスに属するモデルにとって重要な確率論的性質を証明するのが困難となっていた.近年,この問題を解決するものとして対称多項式等を用いた組合せ論的手法に注目が集まってきている.本講演では,最先端の組合せ論的アプローチを用いることで,KPZ普遍クラスの基礎的なモデルであるLast Passage Percolation(LPP)において, Chapman-Kolmogorov equationが容易に得られることを紹介する.

2023/05/02

Operator Algebra Seminars

16:45-18:15   Room #126 (Graduate School of Math. Sci. Bldg.)
Ayoub Hafid (Univ. Tokyo)
KK-theory, localization algebras, and approximation
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

Operator Algebra Seminars

16:45-18:15   Room #126 (Graduate School of Math. Sci. Bldg.)
Ayoub Hafid (Univ. Tokyo)
KK-theory, localization algebras, and approximation
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2023/04/28

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]
Kazuo Habiro (Graduate School of Mathematical Sciences, the University of Tokyo)
On quantum topology (日本語)
[ Abstract ]
I started my research from surgery theory of knots and 3-manifolds. This is related to finite type invariants, which was studied intensively at that time. I obtained a result which characterises the information that is carried by finite type invariants in terms of clasper surgery. After that, I have studied quantum invariants of integral homology spheres, Kirby calculus of framed links, quantum invariants of bottom tangles, functorialization of Le-Murakami-Ohtsuki invariants, quantum fundamental groups and quantum representation variety of 3-manifolds, traces of categorified quantum groups, etc. I would like to reflect on these studies and also discuss future prospects.
[ Reference URL ]
https://u-tokyo-ac-jp.zoom.us/meeting/register/tZIkc-Cvrz4oHNXj_kafJqhU6ZFWCABqgojM

Tokyo-Nagoya Algebra Seminar

13:00-14:30   Online
Please see the reference URL for details on the online seminar.
Takumi Otani (Osaka Univeristy)
Full exceptional collections associated with Bridgeland stability conditions (Japanese)
[ Abstract ]
The space of Bridgeland stability conditions on a triangulated category is important in mirror symmetry and many people develop various techniques to study it. In order to study the homotopy type of the space of stability conditions, Macri studied stability conditions associated with full exceptional collections. Based on his work, Dimitrov-Katzarkov introduced the notion of a full σ-exceptional collection for a stability condition σ.

In this talk, I will explain the relationship between full exceptional collections and stability conditions and some properties. I will also talk about the existence of full σ-exceptional collections for the derived category of an acyclic quiver.
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

Algebraic Geometry Seminar

13:30-15:00   Room #ハイブリッド開催/117 (Graduate School of Math. Sci. Bldg.)
Taro Yoshino (Tokyo)
On the degree of irrationality of complete intersections (Japanese )
[ Abstract ]
The degree of irrationality of a variety X is the minimum degree of a dominant, generically finite rational map from X to a rational variety. This invariant gives a measure of how far X is from being rational. There were some varieties whose degree of irrationality was computed. For example, in 2017, Bastianelli, De Poi, Ein, Lazarsfeld, and Ullery computed the degree of irrationality of very general hypersurfaces of general type by using the positivity of the canonical line bundle. On the other hand, in 2020, Chen and Stapleton obtained the lower bound of the degree of irrationality of very general Fano hypersurfaces by using the reduction of modulo p.
In this talk, we will show that we can obtain the lower bound of the degree of irrationality of very general Fano complete intersections. For obtaining the bound, we make a minor adjustment to Chen--Stapleton's method using the trace map of differential modules.
This talk is based on joint work with Lucas Braune.

2023/04/27

Information Mathematics Seminar

16:50-18:35   Room #128 (Graduate School of Math. Sci. Bldg.)
Tatsuaki Okamoto (NTT)
The basics of cryptography II (Japanese)
[ Abstract ]
Explanation of the basics of cryptography

2023/04/26

Number Theory Seminar

18:00-19:30   Room #117 (Graduate School of Math. Sci. Bldg.)
Live transmission from IHES, Warning: Start time is one hour later than usual.
Dustin Clausen (Institut des Hautes Études Scientifiques)
A Conjectural Reciprocity Law for Realizations of Motives
[ Abstract ]
A motive over a scheme S is a bit of linear algebra which is supposed to "universally" capture the cohomology of smooth proper S-schemes. Motives can be studied via various "realizations", which are objects of more concrete linear algebraic categories attached to S. It is known that over certain S, these different realizations are related to one another via comparison isomorphisms, as in Hodge theory. In this talk, I will try to explain that for completely general S, there is a much more subtle kind of relationship between these realizations, which takes a similar form to classical reciprocity laws in number theory.
[ Reference URL ]
https://indico.math.cnrs.fr/event/9634/

2023/04/25

Tuesday Seminar on Topology

17:00-18:00   Online
Pre-registration required. See our seminar webpage.
Hiraku Nozawa (Ritsumeikan University)
Harmonic measures and rigidity of surface group actions on the circle (JAPANESE)
[ Abstract ]
We study rigidity properties of surface group actions on the circle via harmonic measures on the suspension bundles, which are measures invariant under the heat diffusion along leaves. We will explain a curvature estimate and a Gauss-Bonnet formula for an S^1-connection obtained by taking the average of the flat connection on the suspension bundle with respect to a harmonic measure. As consequences, we give a precise description of the harmonic measure on suspension foliations with maximal Euler number and an alternative proof of semiconjugacy rigidity theorems of Matsumoto and Burger-Iozzi-Wienhard for actions with maximal Euler number. This is joint work with Masanori Adachi and Yoshifumi Matsuda.
[ 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.)
Taihei Oki (The University of Tokyo)
Combinatorial preprocessing methods for differential-algebraic equations (Japanese)
[ Reference URL ]
https://sites.google.com/g.ecc.u-tokyo.ac.jp/utnas-bulletin-board/

2023/04/24

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
On site+Zoom
Takeo Ohsawa (Nogoya Universiry)
Guan's theorems on optimal strong openness and concavity of minimal $L^2$ integrals (日本語)
[ Abstract ]
Motivated by a question of approximating plurisubharmonic (=psh) functions by those with tame singularities, Demailly and Kollar asked several basic questions on the singularities of psh functions. Guan solved two of them effectively in a paper published in 2019. One of their corollaries says the following.

THEOREM. Let $\Omega$ be a pseudoconvex domain in $\mathbb{C}^n$ and let $\varphi$ be a negative psh function on $\Omega$ such that $\int_\Omega{e^{-\varphi}}<\infty$. Then, $e^{-p\varphi}\in L^1_{\text{loc}}$ around $x$ for any $x\in\Omega$ and $p>1$ satisfying the inequality $$
\frac{p}{p-1}>\frac{\int_\Omega{e^{-\varphi}}}{K_\Omega(x)},
$$ where $K_\Omega$ denotes the diagonalized Bergman kernel of $\Omega$.

This remarkable result is a consequence of a basic property of the minimal $L^2$ integrals (=MLI). The main purpose of the talk is to give an outline of the proof of Theorem by explaining the relation between several notions including the MLI which measure the singularities of psh functions. It will also be mentioned that the proof of Theorem is essentially based on the optimal Ohsawa-Takegoshi type extension theorem, which leads to a concavity property of MLI. Recent papers by Guan and his students will be reviewed, too.
[ 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.)
Charles Bordenave (Institut de Mathématiques de Marseille)
Mobility edge, the Poisson Infinite weighted tree of Aldous and Lévy Matrices (English)
[ Abstract ]
Anderson's 1958 paper on wave scattering in disordered media is still of central importance in contemporary mathematical physics. In this talk, we will present recent progress in understanding the phenomena of localization / delocalization of eigenwaves for some random operators. These operators are built on random trees introduced by Aldous and these are the scaling limits of heavy-tailed random matrices, the Lévy matrices. The focus will be put on the existence of a mobility edge, that is to say of かn abrupt transition between localization and delocalization of eigenwaves. It is a work in collaboration with Amol Aggarwal (Columbia) and Patrick Lopatto (NYU).

Infinite Analysis Seminar Tokyo

16:00-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
Takahiko Nobukawa (Kobe University )
Euler type integral formulas and hypergeometric solutions for
variants of the $q$ hypergeometric equations.
(Japanese)
[ Abstract ]
We know that Papperitz's differential equation is essentially obtained from
Gauss' hypergeometric equation by applying a Moebius transformation,
implying that we have Euler type integral formulas or hypergeometric solutions.
The variants of the $q$ hypergeometric equations, introduced by
Hatano-Matsunawa-Sato-Takemura (Funkcial. Ekvac.,2022), are second order
$q$-difference systems which can be regarded as $q$ analoges of Papperitz's equation.
This motivates us for deriving Euler type integral formulas and hypergeometric solutions
for the pertinent $q$-difference systems. If time admits, I explain
the relation with $q$-analogues of Kummer's 24 solutions,
or the variants of multivariate $q$-hypergeometric functions.
This talk is based on the collaboration with Taikei Fujii.

2023/04/21

Tokyo-Nagoya Algebra Seminar

13:00-14:30   Online
Please see the reference URL for details on the online seminar.
Kota Murakami (University of Tokyo)
Categorifications of deformed Cartan matrices (Japanese)
[ Abstract ]
In a series of works of Gei\ss-Leclerc-Schr\″oer, they introduced a version of preprojective algebra associated with a symmetrizable generalized Cartan matrix and its symmetrizer. For finite type, it can be regarded as an un-graded analogue of Jacobian algebra of certain quiver with potential appeared in the theory of (monoidal) categorification of cluster algebras.

In this talk, we will present an interpretation of graded structures of the preprojective algebra of general type, in terms of a multi-parameter deformation of generalized Cartan matrix and relevant combinatorics motivated from several contexts in the theory of quantum loop algebras or quiver $\mathcal{W}$-algebras. From the vantage point of the representation theory of preprojective algebra, we will prove several purely combinatorial properties of these concepts. This talk is based on a joint work with Ryo Fujita (RIMS).
[ Reference URL ]
http://www.math.nagoya-u.ac.jp/~aaron.chan/TNAseminar.html

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