## Seminar information archive

Seminar information archive ～11/15｜Today's seminar 11/16 | Future seminars 11/17～

#### Tokyo Probability Seminar

16:50-18:20 Room #128 (Graduate School of Math. Sci. Bldg.)

**Hiroshi Takahashi**(College of Science and Technology, Nihon University)#### Numerical Analysis Seminar

16:30-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)

Parallel energy-preserving methods for Hamiltonian systems (日本語)

**Yuto Miyatake**(Nagoya University)Parallel energy-preserving methods for Hamiltonian systems (日本語)

### 2015/06/12

#### Geometry Colloquium

10:00-11:30 Room #126 (Graduate School of Math. Sci. Bldg.)

The nonuniqueness of tangent cone at infinity of Ricci-flat manifolds (Japanese)

**Kota Hattori**(Keio University)The nonuniqueness of tangent cone at infinity of Ricci-flat manifolds (Japanese)

[ Abstract ]

For a complete Riemannian manifold (M,g), the Gromov-Hausdorff limit of (M, r^2g) as r to 0 is called the tangent cone at infinity. By the Gromov's Compactness Theorem, there exists tangent cone at infinity for every complete Riemannian manifolds with nonnegative Ricci curvatures. Moreover, if it is Ricci-flat, with Euclidean volume growth and having at least one tangent cone at infinity with a smooth cross section, then it is uniquely determined by the result of Colding and Minicozzi. In this talk I will explain that the assumption of the volume growth is essential for their uniqueness theorem.

For a complete Riemannian manifold (M,g), the Gromov-Hausdorff limit of (M, r^2g) as r to 0 is called the tangent cone at infinity. By the Gromov's Compactness Theorem, there exists tangent cone at infinity for every complete Riemannian manifolds with nonnegative Ricci curvatures. Moreover, if it is Ricci-flat, with Euclidean volume growth and having at least one tangent cone at infinity with a smooth cross section, then it is uniquely determined by the result of Colding and Minicozzi. In this talk I will explain that the assumption of the volume growth is essential for their uniqueness theorem.

### 2015/06/11

#### Applied Analysis

16:00-17:30 Room #128 (Graduate School of Math. Sci. Bldg.)

### 2015/06/10

#### Operator Algebra Seminars

16:45-18:15 Room #122 (Graduate School of Math. Sci. Bldg.)

Dynamics, dimension, and $C^*$-algebras

**David Kerr**(Texas A&M Univ.)Dynamics, dimension, and $C^*$-algebras

### 2015/06/09

#### Tuesday Seminar on Topology

17:00-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)

Symplectic displacement energy for exact Lagrangian immersions (JAPANESE)

**Manabu Akaho**(Tokyo Metropolitan University)Symplectic displacement energy for exact Lagrangian immersions (JAPANESE)

[ Abstract ]

We give an inequality of the displacement energy for exact Lagrangian

immersions and the symplectic area of punctured holomorphic discs. Our

approach is based on Floer homology for Lagrangian immersions and

Chekanov's homotopy technique of continuations. Moreover, we discuss our

inequality and the Hofer--Zehnder capacity.

We give an inequality of the displacement energy for exact Lagrangian

immersions and the symplectic area of punctured holomorphic discs. Our

approach is based on Floer homology for Lagrangian immersions and

Chekanov's homotopy technique of continuations. Moreover, we discuss our

inequality and the Hofer--Zehnder capacity.

### 2015/06/08

#### Seminar on Geometric Complex Analysis

10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)

Mixed Hodge structures and Sullivan's minimal models of Sasakian manifolds (Japanese)

**Hisashi Kasuya**(Tokyo Institute of Technology)Mixed Hodge structures and Sullivan's minimal models of Sasakian manifolds (Japanese)

[ Abstract ]

By the result of Deligne, Griffiths, Morgan and Sullivan, the Malcev completion of the fundamental group of a compact Kahler manifold is quadratically presented. This fact gives good advances in "Kahler group problem" (Which groups can be the fundamental groups of compact Kahler manifolds?) In this talk, we consider the fundamental groups of compact Sasakian manifolds. We show that the Malcev Lie algebra of the fundamental group of a compact 2n+1-dimensional Sasakian manifold with n >= 2 admits a quadratic presentation by using Morgan's bigradings of Sullivan's minimal models of mixed-Hodge diagrams.

By the result of Deligne, Griffiths, Morgan and Sullivan, the Malcev completion of the fundamental group of a compact Kahler manifold is quadratically presented. This fact gives good advances in "Kahler group problem" (Which groups can be the fundamental groups of compact Kahler manifolds?) In this talk, we consider the fundamental groups of compact Sasakian manifolds. We show that the Malcev Lie algebra of the fundamental group of a compact 2n+1-dimensional Sasakian manifold with n >= 2 admits a quadratic presentation by using Morgan's bigradings of Sullivan's minimal models of mixed-Hodge diagrams.

#### Tokyo Probability Seminar

16:50-18:20 Room #128 (Graduate School of Math. Sci. Bldg.)

On a stochastic Rayleigh-Plesset equation and a certain stochastic Navier-Stokes equation

**Satoshi Yokoyama**(Graduate School of Mathematical Sciences, The University of Tokyo)On a stochastic Rayleigh-Plesset equation and a certain stochastic Navier-Stokes equation

### 2015/06/05

#### Geometry Colloquium

10:00-11:30 Room #126 (Graduate School of Math. Sci. Bldg.)

Veech groups of Veech surfaces and periodic points

(日本語)

**Yoshihiko Shinomiya**(Shizuoka University)Veech groups of Veech surfaces and periodic points

(日本語)

[ Abstract ]

Flat surfaces are surfaces with singular Euclidean structures. The Veech group of a flat surface is the group consisting of all matrices inducing affine mappings of the flat surface. In this talk, we give relations between some geometrical values of flat surfaces and the signatures of Veech groups as Fuchsian groups. As an application of these relations, we estimate the numbers of periodic points of certain flat surfaces.

Flat surfaces are surfaces with singular Euclidean structures. The Veech group of a flat surface is the group consisting of all matrices inducing affine mappings of the flat surface. In this talk, we give relations between some geometrical values of flat surfaces and the signatures of Veech groups as Fuchsian groups. As an application of these relations, we estimate the numbers of periodic points of certain flat surfaces.

#### Seminar on Probability and Statistics

16:20-17:30 Room #056 (Graduate School of Math. Sci. Bldg.)

### 2015/06/03

#### Operator Algebra Seminars

16:45-18:15 Room #122 (Graduate School of Math. Sci. Bldg.)

The Furstenberg boundary and $C^*$-simplicity

**Narutaka Ozawa**(RIMS, Kyoto Univ.)The Furstenberg boundary and $C^*$-simplicity

#### Mathematical Biology Seminar

14:55-16:40 Room #128演習室 (Graduate School of Math. Sci. Bldg.)

Population dynamics of fish stock with migration and its management strategy

**Shigehide Iwata**(The graduate school of marine science and technology, Tokyo University of Marine Science and Technology)Population dynamics of fish stock with migration and its management strategy

### 2015/06/01

#### Algebraic Geometry Seminar

15:30-17:00 Room #122 (Graduate School of Math. Sci. Bldg.)

Rank 2 weak Fano bundles on cubic 3-folds (日本語)

**Daizo Ishikawa**(Waseda University)Rank 2 weak Fano bundles on cubic 3-folds (日本語)

[ Abstract ]

A vector bundle on a projective variety is called weak Fano if its

projectivization is a weak Fano manifold. This is a generalization of

Fano bundles.

In this talk, we will obtain a classification of rank 2 weak Fano

bundles on a nonsingular cubic hypersurface in a projective 4-space.

Specifically, we will show that there exist rank 2 indecomposable weak

Fano bundles on it.

A vector bundle on a projective variety is called weak Fano if its

projectivization is a weak Fano manifold. This is a generalization of

Fano bundles.

In this talk, we will obtain a classification of rank 2 weak Fano

bundles on a nonsingular cubic hypersurface in a projective 4-space.

Specifically, we will show that there exist rank 2 indecomposable weak

Fano bundles on it.

#### Tokyo Probability Seminar

16:50-18:20 Room #128 (Graduate School of Math. Sci. Bldg.)

**Masato Hoshino**(Graduate School of Mathematical Sciences, The University of Tokyo)### 2015/05/28

#### Infinite Analysis Seminar Tokyo

17:00-18:30 Room #002 (Graduate School of Math. Sci. Bldg.)

Unitary spherical representations of Drinfeld doubles (JAPANESE)

**Yuki Arano**(Graduate School of Mathematical Sciences, the University of Tokyo)Unitary spherical representations of Drinfeld doubles (JAPANESE)

[ Abstract ]

It is known that the Drinfeld double of the quantized

enveloping algebra of a semisimple Lie algebra looks similar to the

quantized enveloping algebra of the complexification of the Lie algebra.

In this talk, we investigate the unitary representation theory of such

Drinfeld double via its analogy to that of the complex Lie group.

We also talk on an application to operator algebras.

It is known that the Drinfeld double of the quantized

enveloping algebra of a semisimple Lie algebra looks similar to the

quantized enveloping algebra of the complexification of the Lie algebra.

In this talk, we investigate the unitary representation theory of such

Drinfeld double via its analogy to that of the complex Lie group.

We also talk on an application to operator algebras.

### 2015/05/27

#### Operator Algebra Seminars

16:45-18:15 Room #122 (Graduate School of Math. Sci. Bldg.)

Vertex operator algebras in umbral Moonshine

**John F. R. Duncan**(Case Western Reserve Univ.)Vertex operator algebras in umbral Moonshine

#### Number Theory Seminar

17:00-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)

On a good reduction criterion for polycurves with sections (Japanese)

**Ippei Nagamachi**(University of Tokyo)On a good reduction criterion for polycurves with sections (Japanese)

### 2015/05/26

#### Lie Groups and Representation Theory

17:00-18:30 Room #122 (Graduate School of Math. Sci. Bldg.)

Local functional equations of Clifford quartic forms and homaloidal EKP-polynomials

**Takeyoshi Kogiso**(Josai University)Local functional equations of Clifford quartic forms and homaloidal EKP-polynomials

[ Abstract ]

It is known that one can associate local functional equation to the irreducible relative invariant of an irreducible regular prehomogeneous vector spaces. We construct Clifford quartic forms that cannot obtained from prehomogeneous vector spaces, but, for which one can associate local functional equations. The characterization of polynomials which satisfy local functional equations is an interesting problem. In relation to this characterization problem (in a more general form), Etingof, Kazhdan and Polishchuk raised a conjecture. We make a counter example of this conjecture from Clifford quartic forms. (This is based on the joint work with F.Sato)

It is known that one can associate local functional equation to the irreducible relative invariant of an irreducible regular prehomogeneous vector spaces. We construct Clifford quartic forms that cannot obtained from prehomogeneous vector spaces, but, for which one can associate local functional equations. The characterization of polynomials which satisfy local functional equations is an interesting problem. In relation to this characterization problem (in a more general form), Etingof, Kazhdan and Polishchuk raised a conjecture. We make a counter example of this conjecture from Clifford quartic forms. (This is based on the joint work with F.Sato)

#### Tuesday Seminar on Topology

17:00-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)

Introduction to formalization of topology using a proof assistant. (JAPANESE)

**Ken'ichi Kuga**(Chiba University)Introduction to formalization of topology using a proof assistant. (JAPANESE)

[ Abstract ]

Although the program of formalization goes back to David

Hilbert, it is only recently that we can actually formalize

substantial theorems in modern mathematics. It is made possible by the

development of certain type theory and a computer software called a

proof assistant. We begin this talk by showing our formalization of

some basic geometric topology using a proof assistant COQ. Then we

introduce homotopy type theory (HoTT) of Voevodsky et al., which

interprets type theory from abstract homotopy theoretic perspective.

HoTT proposes "univalent" foundation of mathematics which is

particularly suited for computer formalization.

Although the program of formalization goes back to David

Hilbert, it is only recently that we can actually formalize

substantial theorems in modern mathematics. It is made possible by the

development of certain type theory and a computer software called a

proof assistant. We begin this talk by showing our formalization of

some basic geometric topology using a proof assistant COQ. Then we

introduce homotopy type theory (HoTT) of Voevodsky et al., which

interprets type theory from abstract homotopy theoretic perspective.

HoTT proposes "univalent" foundation of mathematics which is

particularly suited for computer formalization.

### 2015/05/25

#### Seminar on Geometric Complex Analysis

10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)

On uniform K-stability (Japanese)

**Tomoyuki Hisamoto**(Nagoya Univ.)On uniform K-stability (Japanese)

[ Abstract ]

It is a joint work with Sébastien Boucksom and Mattias Jonsson. We first introduce functionals on the space of test configurations, as non-Archimedean analogues of classical functionals on the space of Kähler metrics. Then, uniform K-stability is defined as a counterpart of K-energy's coercivity condition. Finally, reproving and strengthening Y. Odaka's results, we study uniform K-stability of Kähler-Einstein manifolds.

It is a joint work with Sébastien Boucksom and Mattias Jonsson. We first introduce functionals on the space of test configurations, as non-Archimedean analogues of classical functionals on the space of Kähler metrics. Then, uniform K-stability is defined as a counterpart of K-energy's coercivity condition. Finally, reproving and strengthening Y. Odaka's results, we study uniform K-stability of Kähler-Einstein manifolds.

#### Algebraic Geometry Seminar

15:30-17:00 Room #122 (Graduate School of Math. Sci. Bldg.)

Good reduction of K3 surfaces (日本語 or English)

http://www.ms.u-tokyo.ac.jp/~ymatsu/index_j.html

**Yuya Matsumoto**(University of Tokyo)Good reduction of K3 surfaces (日本語 or English)

[ Abstract ]

We consider degeneration of K3 surfaces over a 1-dimensional base scheme

of mixed characteristic (e.g. Spec of the p-adic integers).

Under the assumption of potential semistable reduction, we first prove

that a trivial monodromy action on the l-adic etale cohomology group

implies potential good reduction, where potential means that we allow a

finite base extension.

Moreover we show that a finite etale base change suffices.

The proof for the first part involves a mixed characteristic

3-dimensional MMP (Kawamata) and the classification of semistable

degeneration of K3 surfaces (Kulikov, Persson--Pinkham, Nakkajima).

For the second part, we consider flops and descent arguments. This is a joint work with Christian Liedtke.

[ Reference URL ]We consider degeneration of K3 surfaces over a 1-dimensional base scheme

of mixed characteristic (e.g. Spec of the p-adic integers).

Under the assumption of potential semistable reduction, we first prove

that a trivial monodromy action on the l-adic etale cohomology group

implies potential good reduction, where potential means that we allow a

finite base extension.

Moreover we show that a finite etale base change suffices.

The proof for the first part involves a mixed characteristic

3-dimensional MMP (Kawamata) and the classification of semistable

degeneration of K3 surfaces (Kulikov, Persson--Pinkham, Nakkajima).

For the second part, we consider flops and descent arguments. This is a joint work with Christian Liedtke.

http://www.ms.u-tokyo.ac.jp/~ymatsu/index_j.html

#### Tokyo Probability Seminar

16:50-18:20 Room #128 (Graduate School of Math. Sci. Bldg.)

A finite diameter theorem on RCD spaces

**Yu Kitabeppu**(Graduate School of Sciences, Kyoto University)A finite diameter theorem on RCD spaces

### 2015/05/21

#### Lectures

16:00-17:00 Room #056 (Graduate School of Math. Sci. Bldg.)

The Shape of Data

(ENGLISH)

http://faculty.ms.u-tokyo.ac.jp/Carlsson.html

**Gunnar Carlsson**(Stanford University, Ayasdi INC)The Shape of Data

(ENGLISH)

[ Abstract ]

There is a tremendous amount of attention being paid to the notion of

"Big Data". In many situations, however, the problem is not so much the

size of the data but rather its complexity. This observation shows that

it is now important to find methods for representing complex data in a

compressed and understandable fashion. Representing data by shapes

turns out to be useful in many situations, and therefore topology, the

mathematical sub discipline which studies shape, becomes quite

relevant. There is now a collection of methods based on topology for

analyzing complex data, and in this talk we will discuss these methods,

with numerous examples.

[ Reference URL ]There is a tremendous amount of attention being paid to the notion of

"Big Data". In many situations, however, the problem is not so much the

size of the data but rather its complexity. This observation shows that

it is now important to find methods for representing complex data in a

compressed and understandable fashion. Representing data by shapes

turns out to be useful in many situations, and therefore topology, the

mathematical sub discipline which studies shape, becomes quite

relevant. There is now a collection of methods based on topology for

analyzing complex data, and in this talk we will discuss these methods,

with numerous examples.

http://faculty.ms.u-tokyo.ac.jp/Carlsson.html

### 2015/05/20

#### Number Theory Seminar

17:30-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)

Colmez' conjecture in average (English)

**Shou-Wu Zhang**(Princeton University)Colmez' conjecture in average (English)

[ Abstract ]

This is a report on a joint work with Xinyi Yuan on a conjectured formula of Colmez about the Faltings heights of CM abelian varieties. I will sketch a deduction of this formula in average of CM types from our early work on Gross-Zagier formula. When combined with a recent work of Tsimerman, this result implies the Andre-Oort conjecture for the moduli of abelian varieties.

Our method is different than a recently announced proof of a weaker form of the average formula by Andreatta, Howard, Goren, and Madapusi Pera: we use neither high dimensional Shimura varieties nor Borcherds' liftings.

This is a report on a joint work with Xinyi Yuan on a conjectured formula of Colmez about the Faltings heights of CM abelian varieties. I will sketch a deduction of this formula in average of CM types from our early work on Gross-Zagier formula. When combined with a recent work of Tsimerman, this result implies the Andre-Oort conjecture for the moduli of abelian varieties.

Our method is different than a recently announced proof of a weaker form of the average formula by Andreatta, Howard, Goren, and Madapusi Pera: we use neither high dimensional Shimura varieties nor Borcherds' liftings.

#### Operator Algebra Seminars

16:45-18:15 Room #122 (Graduate School of Math. Sci. Bldg.)

Unique prime factorization and bicentralizer problem for a class of type III factors

**Yusuke Isono**(RIMS, Kyoto Univ.)Unique prime factorization and bicentralizer problem for a class of type III factors

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