Seminar information archive

Seminar information archive ~06/22Today's seminar 06/23 | Future seminars 06/24~

Lie Groups and Representation Theory

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Yuichiro Tanaka (Institute of Mathematics for Industry, Kyushu University)
Visible actions of compact Lie groups on complex spherical varieties (English)
[ Abstract ]
With the aim of uniform treatment of multiplicity-free representations of Lie groups, T. Kobayashi introduced the theory of visible actions on complex manifolds.

In this talk we consider visible actions of a compact real form U of a connected complex reductive algebraic group G on G-spherical varieties. Here a complex G-variety X is said to be spherical if a Borel subgroup of G has an open orbit on X. The sphericity implies the multiplicity-freeness property of the space of polynomials on X. Our main result gives an abstract proof for the visibility of U-actions. As a corollary, we obtain an alternative proof for the visibility of U-actions on linear multiplicity-free spaces, which was earlier proved by A. Sasaki (2009, 2011), and the visibility of U-actions on generalized flag varieties, earlier proved by Kobayashi (2007) and T- (2013, 2014).

2015/04/13

Tokyo Probability Seminar

16:50-17:50   Room #128 (Graduate School of Math. Sci. Bldg.)
Hans Rudolf Kuensch (ETH Zurich)
Modern Monte Carlo methods -- Some examples and open questions (ENGLISH)
[ Abstract ]
Probability and statistics once had strong relations, but in recent years the two fields have moved into opposite directions. Despite this, I believe that both fields would profit if they continued to interact. Monte Carlo methods are one topic that is of interest to both probability and statistics: Statisticians use advanced Monte Carlo methods, and analyzing these methods is a challenge for probabilists. I will illustrate this, using as examples rare event estimation by sample splitting, approximate Bayesian computation and Monte Carlo filters.

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Yu Yasufuku (Nihon Univ.)
Campana's Multiplicity and Integral Points on P^2 (English)
[ Abstract ]
We analyze when the complements of (possibly reducible) curves in P^2 have Zariski-dense integral points. The analysis utilizes the structure theories for affine surfaces based on logarithmic Kodaira dimension. When the log Kodaira dimension is one, an important role is played by Campana's multiplicity divisors for fibrations, but there are some subtleties. This is a joint work with Aaron Levin (Michigan State).

Algebraic Geometry Seminar

15:30-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Frédéric Campana (Université de Lorraine)
An orbifold version of Miyaoka's semi-positivity theorem and applications (English)
[ Abstract ]
This `orbifold' version of Miyaoka's theorem says that if (X,D)
is a projective log-canonical pair with K_X+D pseudo-effective,
then its 'cotangent' sheaf $¥Omega^1(X,D)$ is generically semi-positive.
The definitions will be given. The original proof of Miyaoka, which
mixes
char 0 and char p>0 arguments could not be adapted. Our proof is in char
0 only.

A first consequence is when (X,D) is log-smooth with reduced boudary D,
in which case the cotangent sheaf is the classical Log-cotangent sheaf:
if some tensor power of $¥omega^1_X(log(D))$ contains a 'big' line
bundle, then K_X+D is 'big' too. This implies, together with work of
Viehweg-Zuo,
the `hyperbolicity conjecture' of Shafarevich-Viehweg.

The preceding is joint work with Mihai Paun.

A second application (joint work with E. Amerik) shows that if D is a
non-uniruled smooth divisor in aprojective hyperkaehler manifold with
symplectic form s,
then its characteristic foliation is algebraic only if X is a K3 surface.
This was shown previously bt Hwang-Viehweg assuming D to be of general
type. This result has some further consequences.

2015/04/10

Seminar on Probability and Statistics

14:50-16:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Yacine Ait-Sahalia (Princeton University)
Principal Component Analysis of High Frequency Data (joint with Dacheng Xiu)
[ Abstract ]
We develop a methodology to conduct principal component analysis of high frequency financial data. The procedure involves estimation of realized eigenvalues, realized eigenvectors, and realized principal components and we provide the asymptotic distribution of these estimators. Empirically, we study the components of the constituents of Dow Jones Industrial Average Index, in a high frequency version, with jumps, of the Fama-French analysis. Our findings show that, excluding jump variation, three Brownian factors explain between 50 and 60% of continuous variation of the stock returns. Their explanatory power varies over time. During crises, the first principal component becomes increasingly dominant, explaining up to 70% of the variation on its own, a clear sign of systemic risk.

2015/04/08

Operator Algebra Seminars

16:45-18:15   Room #122 (Graduate School of Math. Sci. Bldg.)
Yoshikata Kida (Univ. Tokyo)
On treeable equivalence relations arising from the Baumslag-Solitar groups
(English)

Number Theory Seminar

17:30-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Seidai Yasuda (Osaka University)
Integrality of $p$-adic multiple zeta values and application to finite multiple zeta values.
(English)
[ Abstract ]
I will give a proof of an integrality of p-adic multiple zeta values. I would also like to explain how it can be applied to give an upper bound of the dimension of finite multiple zeta values.

2015/04/07

Tuesday Seminar on Topology

17:00-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Kazushi Ueda (The University of Tokyo)
Potential functions for Grassmannians (JAPANESE)
[ Abstract ]
Potential functions are Floer-theoretic invariants
obtained by counting Maslov index 2 disks
with Lagrangian boundary conditions.
In the talk, we will discuss our joint work
with Yanki Lekili and Yuichi Nohara
on Lagrangian torus fibrations on the Grassmannian
of 2-planes in an n-space,
the potential functions of their Lagrangian torus fibers,
and their relation with mirror symmetry for Grassmannians.

Lie Groups and Representation Theory

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Bent Orsted (Aarhus University)
Branching laws and elliptic boundary value problems
(English)
[ Abstract ]
Classically the Poisson transform relates harmonic functions in the complex upper half plane to their boundary values on the real axis. In
some recent work by Caffarelli et al. some new generalizations of this appears in connection with the fractional Laplacian. In this lecture we
shall explain how the symmetry-breaking operators introduced by T. Kobayashi for studying branching laws may shed new light on the situation for elliptic boundary value problems. This is based on joint work with J. M\"o{}llers and G. Zhang.

2015/04/06

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Ken-ichi Yoshikawa (Kyoto Univ.)
Analytic torsion for K3 surfaces with involution (Japanese)
[ Abstract ]
In 2004, I introduced a holomorphic torsion invariant for 2-elementary K3 surfaces, i.e., K3 surfaces with involution. In the talk, I will report a recent progress in this invariant. Namely, for all possible deformation types, the holomorphic torsion invariant viewed as a function on the moduli space, is expressed as the product of an explicit Borcherds lift and an explicit Siegel modular form. If time permits, I will interpret the result in terms of the BCOV invariant, i.e., the genus-one string amplitude in B-model, for Calabi-Yau threefolds of Borcea-Voisin. This is a joint work with Shouhei Ma.

2015/03/24

Tuesday Seminar on Topology

17:00-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Mina Aganagic (University of California, Berkeley)
Knots and Mirror Symmetry (ENGLISH)
[ Abstract ]
I will describe two conjectures relating knot theory and mirror symmetry. One can associate, to every knot K, one a Calabi-Yau manifold Y(K), which depends on the homotopy type of the knot only. The first conjecture is that Y(K) arises by a generalization of SYZ mirror symmetry, as mirror to the conifold, O(-1)+O(-1)->P^1. The second conjecture is that topological string provides a quantization of Y(K) which leads to quantum HOMFLY invariants of the knot. The conjectures are based on joint work with C. Vafa and also with T.Ekholm, L. Ng.

Lie Groups and Representation Theory

18:00-19:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Piotr Pragacz (Institute of Mathematics, Polish Academy of Sciences)
A Gysin formula for Hall-Littlewood polynomials
[ Abstract ]
Schubert calculus on Grassmannians is governed by Schur S-functions, the one on Lagrangian Grassmannians by Schur Q-functions. There were several attempts to give a unifying approach to both situations.
We propose to use Hall-Littlewood symmetric polynomials. They appeared implicitly in Hall's study of the combinatorial lattice structure of finite abelian p-groups and in Green's calculations of the characters of GL(n) over finite fields; they appeared explicitly in the work of Littlewood on some problems in representation theory.
With the projection in a Grassmann bundle, there is associated its Gysin map, induced by pushing forward cycles (topologists call it "integration along fibers").
We state and prove a Gysin formula for HL-polynomials in these bundles. We discuss its two specializations, giving better insights to previously known formulas for Schur S- and P-functions.

2015/03/20

Numerical Analysis Seminar

13:30-15:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Gadi Fibich (Tel Aviv University)
Asymmetric Auctions (English)
[ Abstract ]
Auctions are central to the modern economy, both on-line and off-line. A fundamental result in auction theory is that when bidders are symmetric (identical), then under quite general conditions, all auctions are revenue equivalent. While it is known that this result does not hold when bidders are asymmetric, the effect of bidders' asymmetry is poorly understood, since asymmetric auctions are much harder to analyze.

In this talk I will discuss the mathematical theory of asymmetric auctions. I will focus on asymmetric first-price auctions, where the mathematical model is given by a nonstandard system of $n$ nonlinear ordinary differential equations, with $2n$ boundary conditions and a free boundary. I will present various analytic and numerical approaches for this system. Then I will present some recent results on asymptotic revenue equivalence of asymmetric auctions.

Joint work with A. Gavious and N. Gavish.

2015/03/19

FMSP Lectures

9:00-11:00   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Matthew Gursky (Univ. Nortre Dame) 9:00-9:50
Critical metrics for quadratic Riemannian functionals in dimension four (ENGLISH)
[ Abstract ]
In these lectures I will give an overview of a proof of existence, via gluing methods, of metrics which are critical points of quadratic Riemannian functionals. This is a joint project with J. Viaclovsky.
These are functionals on the space of metrics which are given by integrals of quadratic polynomials in the curvature tensor. Our approach is to construct these metrics on connected sums of Einstein four-manifolds, specifically the Fubini-Study metric on CP2 and the product metric on S2 X S2. Using these metrics in various gluing configurations, toric-invariant critical metrics are found on connected sums for a specific quadratic functional, which depends on the global geometry of the factors.
I will also explain some recent work which attempts to understand the moduli space of critical metrics.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses
Gábor Székelyhidi (Univ. Nortre Dame) 10:10-11:00
Hessian type equations on compact Kähler manifolds (ENGLISH)
[ Abstract ]
I will discuss a priori estimates for a general class of nonlinear equations on compact Kähler manifolds. This unifies and generalizes several previous works on specific equations, such as the complex Monge-Ampère, Hessian, and inverse Hessian equations.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses

2015/03/18

FMSP Lectures

9:00-11:00   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Matthew Gursky (Univ. Nortre Dame) 9:00-9:50
Critical metrics for quadratic Riemannian functionals in dimension four (ENGLISH)
[ Abstract ]
In these lectures I will give an overview of a proof of existence, via gluing methods, of metrics which are critical points of quadratic Riemannian functionals. This is a joint project with J. Viaclovsky.
These are functionals on the space of metrics which are given by integrals of quadratic polynomials in the curvature tensor. Our approach is to construct these metrics on connected sums of Einstein four-manifolds, specifically the Fubini-Study metric on CP2 and the product metric on S2 X S2. Using these metrics in various gluing configurations, toric-invariant critical metrics are found on connected sums for a specific quadratic functional, which depends on the global geometry of the factors.
I will also explain some recent work which attempts to understand the moduli space of critical metrics.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses
Gábor Székelyhidi (Univ. Nortre Dame) 10:10-11:00
Hessian type equations on compact Kähler manifolds (ENGLISH)
[ Abstract ]
I will discuss a priori estimates for a general class of nonlinear equations on compact Kähler manifolds. This unifies and generalizes several previous works on specific equations, such as the complex Monge-Ampère, Hessian, and inverse Hessian equations.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses

2015/03/17

FMSP Lectures

13:30-15:00, 15:30-17:30   Room #Balcony A, Kavli IPMU (Graduate School of Math. Sci. Bldg.)
Hiroshi Iritani (Kyoto University)
Toric mirror symmetry via shift operators (ENGLISH)
[ Abstract ]
Recently, shift operator for equivariant quantum cohomology
has been introduced in the work of Braverman, Maulik, Okounkov and
Pandharipande. This can be viewed as an equivariant lift of the
Seidel representation, and intertwines quantum connections with
different equivariant parameters.
In this series of talks, I will explain that shift operators essentially
"reconstruct" mirrors of toric varieties. More precisely we obtain the
following from basic properties of shift operators:

1. Givental's mirror theorem.
2. Landau-Ginzburg potential and primitive form.
3. Extended I-functions.

We will also see that the Gamma integral structure arises as
a solution to the difference equation defined by shift operators.
[ Reference URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Iritani.pdf

FMSP Lectures

9:00-11:00   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Matthew Gursky (Univ. Nortre Dame) 9:00-9:50
Critical metrics for quadratic Riemannian functionals in dimension four (ENGLISH)
[ Abstract ]
In these lectures I will give an overview of a proof of existence, via gluing methods, of metrics which are critical points of quadratic Riemannian functionals. This is a joint project with J. Viaclovsky.
These are functionals on the space of metrics which are given by integrals of quadratic polynomials in the curvature tensor. Our approach is to construct these metrics on connected sums of Einstein four-manifolds, specifically the Fubini-Study metric on CP2 and the product metric on S2 X S2. Using these metrics in various gluing configurations, toric-invariant critical metrics are found on connected sums for a specific quadratic functional, which depends on the global geometry of the factors.
I will also explain some recent work which attempts to understand the moduli space of critical metrics.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses
Gábor Székelyhidi (Univ. Nortre Dame) 10:10-11:00
Hessian type equations on compact Kähler manifolds (ENGLISH)
[ Abstract ]
I will discuss a priori estimates for a general class of nonlinear equations on compact Kähler manifolds. This unifies and generalizes several previous works on specific equations, such as the complex Monge-Ampère, Hessian, and inverse Hessian equations.
[ Reference URL ]
https://sites.google.com/site/princetontokyo/mini-courses

2015/03/16

FMSP Lectures

13:30-15:00, 15:30-17:30   Room #Balcony A, Kavli IPMU (Graduate School of Math. Sci. Bldg.)
Hiroshi Iritani (Kyoto University)
Toric mirror symmetry via shift operators (ENGLISH)
[ Abstract ]
Recently, shift operator for equivariant quantum cohomology
has been introduced in the work of Braverman, Maulik, Okounkov and
Pandharipande. This can be viewed as an equivariant lift of the
Seidel representation, and intertwines quantum connections with
different equivariant parameters.
In this series of talks, I will explain that shift operators essentially
"reconstruct" mirrors of toric varieties. More precisely we obtain the
following from basic properties of shift operators:

1. Givental's mirror theorem.
2. Landau-Ginzburg potential and primitive form.
3. Extended I-functions.

We will also see that the Gamma integral structure arises as
a solution to the difference equation defined by shift operators.
[ Reference URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Iritani.pdf

2015/03/13

Colloquium

14:00-15:00   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Takayuki Oda (Graduate School of Mathematical Sciences, University of Tokyo)

[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~takayuki/index-j.html

Colloquium

16:30-17:30   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Shigeo KUSUOKA (Graduate School of Mathematical Sciences, University of Tokyo)
(JAPANESE)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/teacher/kusuoka.html

Colloquium

15:10-16:10   Room #大講義室 (Graduate School of Math. Sci. Bldg.)
Yoichi Miyaoka (Graduate School of Mathematical Sciences, University of Tokyo)
(JAPANESE)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/teacher/miyaoka.html

2015/03/10

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Andrei Pajitnov (Univ. de Nantes)
Arnold conjecture, Floer homology,
and augmentation ideals of finite groups.
(ENGLISH)
[ Abstract ]
Let H be a generic time-dependent 1-periodic
Hamiltonian on a closed weakly monotone
symplectic manifold M. We construct a refined version
of the Floer chain complex associated to (M,H),
and use it to obtain new lower bounds for the number P(H)
of the 1-periodic orbits of the corresponding hamiltonian
vector field. We prove in particular that
if the fundamental group of M is finite
and solvable or simple, then P(H)
is not less than the minimal number
of generators of the fundamental group.

This is joint work with Kaoru Ono.

2015/02/24

thesis presentations

15:00-16:15   Room #128 (Graduate School of Math. Sci. Bldg.)
小池 祐太 (情報・システム研究機構 統計数理研究所)
Covariance Estimation from Ultra-High-Frequency Date(超高頻度データに対する共分散推定) (JAPANESE)

2015/02/23

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Zhenghan Wang (Microsoft Research Station Q)
Classification of (2+1)-TQFTs and its applications to physics and quantum computation (English)

2015/02/19

Infinite Analysis Seminar Tokyo

13:30-17:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Shunsuke Tsuji (Graduate School of Mathematical Sciences, the University of Tokyo) 13:30-15:00
Skein algebra and mapping class group (JAPANESE)
[ Abstract ]
We define some filtrations of skein modules and the skein algebra on an oriented surface, and define the completed skein modules and
the completed skein algebra of the surface with respect to these filtration. We give an explicit formula for the action of the Dehn
twists on the completed skein modules in terms of the action of the completed skein algebra of the surface. As an application, we describe the action of the Johnson kernel on the completed skein modules.
Yuta Nozaki (Graduate School of Mathematical Sciences, the University of Tokyo) 15:30-17:00
An extension of the LMO functor (JAPANESE)
[ Abstract ]
Cheptea, Habiro and Massuyeau introduced the LMO functor as an extension of the LMO invariant of closed 3-manifolds. The LMO functor is “the monoidal category of Lagrangian cobordisms between surfaces with at most one boundary component” to “the monoidal category of top-substantial Jacobi diagrams”. In this talk, we extend the LMO functor to the case of any number of boundary components. Moreover, we explain that the internal degree d part of the extension is a finite-type invariant of degree d.

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