## 過去の記録

### 2015年07月07日(火)

#### トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea : 16:30-17:00 Common Room

Representation varieties detect essential surfaces (JAPANESE)
[ 講演概要 ]
Extending Culler-Shalen theory, Hara and I presented a way to construct
certain kinds of branched surfaces (possibly without any branch) in a 3-
manifold from an ideal point of a curve in the SL_n-character variety.
There exists an essential surface in some 3-manifold known to be not
detected in the classical SL_2-theory. We show that every essential
surface in a 3-manifold is given by the ideal point of a line in the SL_
n-character variety for some n. The talk is partially based on joint
works with Stefan Friedl and Matthias Nagel, and also with Takashi Hara.

### 2015年07月06日(月)

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 126号室

On the structure of holomorphic automorphism groups of generalized complex ellipsoids and generalized Hartogs triangles (JAPANESE)
[ 講演概要 ]
In this talk, we first review the structure of holomorphic automorphism groups of generalized complex ellipsoids and, as an application of this, we clarify completely the structure of generalized Hartogs triangles. Finally, if possible, I will mention some known results on proper holomorphic self-mappings of generalized complex ellipsoids, generalized Hartogs triangles, and discuss a related question to these results.

### 2015年07月03日(金)

#### 幾何コロキウム

10:00-11:30   数理科学研究科棟(駒場) 126号室

[ 講演概要 ]
Let G be a non-compact semisimple Lie group. We take a pair of symmetric pairs (G,H) and (G,L) such that the diagonal action of G on G/H \times G/L is proper. In this talk, we show that by taking the compact dual of triple (G,H,L)'', we obtain a compact symmetric space M = U/K and its reflective submanifolds S_1 and S_2 satisfying that the intersection of S_1 and gS_2 is discrete in M for any g in U. In particular, we give a classification of such triples (G,H,L).

### 2015年07月01日(水)

#### 作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 122号室

Approximate unitary equivalence of finite index endomorphisms of the AFD
factors

### 2015年06月30日(火)

#### Lie群論・表現論セミナー

17:00-18:30   数理科学研究科棟(駒場) 122号室
Anatoly Vershik 氏 (St. Petersburg Department of Steklov Institute of Mathematics)
Random subgroups and representation theory
[ 講演概要 ]
The following problem had been appeared independently in different teams and various reason:
to describe the Borel measures on the lattice of all subgroups of given group, which are invariant with respect to the action of the group by conjugacy. The main interest of course represents nonatomic measures which exist not for any group.
I will explain how these measures connected with characters and representations of the group, and describe the complete list of such measures for infinite symmetric group.

#### トポロジー火曜セミナー

17:30-18:30   数理科学研究科棟(駒場) 056号室
Tea : 17:00-17:30 Common Room

The Cannon-Thurston maps and the canonical decompositions of punctured surface bundles over the circle (JAPANESE)
[ 講演概要 ]
To each once-punctured-torus bundle over the circle with pseudo-Anosov monodromy,
there are associated two tessellations of the complex plane:
one is the triangulation of a horosphere induced by the canonical decomposition into ideal tetrahedra,
and the other is a fractal tessellation given by the Cannon-Thurston map of the fiber group.
In a joint work with Warren Dicks, I had described the relation between these two tessellations.
This result was recently generalized by Francois Gueritaud to punctured surface bundles
with pseudo-Anosov monodromy where all singuraities of the invariant foliations are at punctures.
In this talk, I will explain Gueritaud's work and related work by Naoki Sakata.

### 2015年06月29日(月)

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 126号室

Cohomology Formula for Obstructions to Asymptotic Chow semistability (JAPANESE)
[ 講演概要 ]
Odaka and Wang proved the intersection formula for the Donaldson-Futaki invariant. We generalize this result for the higher Futaki invariants which are obstructions to asymptotic Chow semistability.

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
Manfred Lehn 氏 (Mainz/RIMS)
Twisted cubics and cubic fourfolds (English)
[ 講演概要 ]
The moduli scheme of generalised twisted cubics on a smooth
cubic fourfold Y non containing a plane is smooth projective of
dimension 10 and admits a contraction to an 8-dimensional
holomorphic symplectic manifold Z(Y). The latter is shown to be
birational to the Hilbert scheme of four points on a K3 surface if
Y is of Pfaffian type. This is a report on joint work with C. Lehn,
C. Sorger and D. van Straten and with N. Addington.

#### 東京確率論セミナー

16:50-18:20   数理科学研究科棟(駒場) 128号室

[ 講演概要 ]

よく知られた保険会社の収支モデル(Lundberg model) では, T_0 が倒産時刻となる.

$$v (x) ={\mathbf E}_x \big[ e^{- \alpha \, T_0 + i \, \beta \, X(T_0) }\, \big], \quad x \geq 0, \ \alpha \geq 0, \ \beta \in {\mathbb R}^1.$$
の具体型を以下の方法で求めた.
(i) $v(0)$ を Feller の補題を利用して計算,
(ii) $v(x)$ が満たす積分微分方程式を用意し, $v(0)$ から $v(x)$ を導出.

D は確率測度空間の中の dense subset なので, これにより,

や \,truncated exponential distribution\,'' の場合にも, 新たに

#### 数値解析セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室

Stabilized Runge-Kutta methods for the weak approximation of solutions of stochastic differential equations (日本語)
[ 講演概要 ]
We are concerned with numerical methods which give weak approximations for stiff It\^{o} stochastic differential equations (SDEs). Implicit methods are one of good candidates to deal with such SDEs. In fact, a well-designed implicit method has been recently proposed by Abdulle and his colleagues [Abdulle et al. 2013a]. On the other hand, it is well known that the numerical solution of stiff SDEs leads to a stepsize reduction when explicit methods are used. However, there are some classes of explicit methods that are well suited to solving some types of stiff SDEs. One such class is the class of stochastic orthogonal Runge-Kutta Chebyshev (SROCK) methods [Abdulle et al. 2013b]. SROCK methods reduce to Runge-Kutta Chebyshev methods when applied to ordinary differential equations (ODEs). Another promising class of methods is the class of explicit methods that reduce to explicit exponential Runge-Kutta (RK) methods [Hochbruck et al. 2005, 2010] when applied to semilinear ODEs.
In this talk, we will propose new exponential RK methods which achieve weak order two for multi-dimensional, non-commutative SDEs with a semilinear drift term. We will analytically investigate their stability properties in mean square, and will check their performance in numerical experiments.
(This is a joint work with D. Cohen and K. Burrage.)

#### 作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室
Vaughan F. R. Jones 氏 (Vanderbilt University)
Block spin renormalization and R. Thompson's groups F and T

### 2015年06月26日(金)

#### 談話会・数理科学講演会

16:50-17:50   数理科学研究科棟(駒場) 056号室

ダイマー模型とミラー対称性
(JAPANESE)
[ 講演概要 ]
ダイマー模型は1930年代に統計力学的な模型として導入され、
Ising模型を特別な場合として含む重要な研究対象であるが、

### 2015年06月25日(木)

#### 東京無限可積分系セミナー

17:00-18:30   数理科学研究科棟(駒場) 002号室

４次元自励パンルヴェ型方程式と種数２の曲線の退化 (JAPANESE)
[ 講演概要 ]
パンルヴェ型方程式は楕円関数の満たす微分方程式の拡張の一つとして考えられた８種類の２階非線形微分方程式であるが、線形方程式のモノドロミー保存変形、ソリトン方程式の相似簡約、数理物理や表現論との関わりの中で詳しく研究されてきた。個々の側面に着目した差分類似や高階への拡張も多数提案される中、最近４次元パンルヴェ型微分方程式は線形方程式の観点から分類がなされた(Sakai, Kawakami-N.-Sakai, Kawakami)。このセミナーでは４次元パンルヴェ型方程式を自励化して得られる４０個の可積分系の方程式をそれらのスペクトラル曲線(種数２の代数曲線である)の退化(浪川－上野型)を調べることで特徴付ける試みについて説明する。

### 2015年06月24日(水)

#### 作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 122号室
Matthew Cha 氏 (UC Davis)
Gapped ground state phases, topological order and anyons

### 2015年06月23日(火)

#### トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea : 16:30-17:00 Common Room

Box complexes and model structures on the category of graphs (JAPANESE)
[ 講演概要 ]
To determine the chromatic numbers of graphs, so-called the graph
coloring problem, is one of the most classical problems in graph theory.
Box complex is a Z_2-space associated to a graph, and it is known that
its equivariant homotopy invariant is related to the chromatic number.

Csorba showed that for each finite Z_2-CW-complex X, there is a graph
whose box complex is Z_2-homotopy equivalent to X. From this result, I
expect that the usual model category of Z_2-topological spaces is
Quillen equivalent to a certain model structure on the category of
graphs, whose weak equivalences are graph homomorphisms inducing Z_2-
homotopy equivalences between their box complexes.

In this talk, we introduce model structures on the category of graphs
whose weak equivalences are described as above. We also compare our
model categories of graphs with the category of Z_2-topological spaces.

### 2015年06月22日(月)

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
Martí Lahoz 氏 (Institut de Mathématiques de Jussieu )
Rational cohomology tori
(English)
[ 講演概要 ]
Complex tori can be topologically characterised among compact Kähler
manifolds by their integral cohomology ring. I will discuss the
structure of compact Kähler manifolds whose rational cohomology ring is
isomorphic to the rational cohomology ring of a torus and give some
examples. This is joint work with Olivier Debarre and Zhi Jiang.
[ 講演参考URL ]
http://webusers.imj-prg.fr/~marti.lahoz/

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 126号室

Amoebas and Horn hypergeometric functions
[ 講演概要 ]
Since 10 years, the utility of the Horn hypergeometric functions in Algebraic Geometry has been recognized in a small circle of specialists. The main reason for this interest lies in the fact that every period integral of an affine non-degenerate complete intersection variety can be described as a Horn hypergeometric function (HGF). Therefore the monodromy of the middle dimensional homology can be calculated as the monodromy of an Horn HGF’s.
There is a slight difference between the Gel’fand-Kapranov-Zelevinski HGF’s and the Horn HGF’s. The latter may contain so called “persistent polynomial solutions” that cannot be mapped to GKZ HGF’s via a natural isomorphism between two spaces of HGF’s. In this talk, I will review basic facts on the Horn HGF’s. As a main tool to study the topology of the discriminant loci together with the
analytic aspects of the story, amoebas – image by the log map of the discriminant- will be highlighted.
As an application of this theory the following theorem can be established. For a bivariate Horn HGF system, its monodromy invariant space is always one dimensional if and only if its Ore-Sato polygon is either a zonotope or a Minkowski sum of a triangle and some segments.
This is a collaboration with Timur Sadykov.

#### 東京確率論セミナー

16:50-18:20   数理科学研究科棟(駒場) 128号室

Lamplighter random walks on fractals

### 2015年06月17日(水)

#### 作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 122号室

Self-adjointness of bound state operators in integrable quantum field theory

#### 代数学コロキウム

17:00-18:00   数理科学研究科棟(駒場) 056号室

Hodge-Tate weights of p-adic Galois representations and Banach representations of GL_2(Q_p)
(Japanese)
[ 講演概要 ]
p進Galois表現のHodge-Tate重みを，p進Langlands対応により対応するGL_2(Q_p)のBanach表現から取り出すことが目標です．Banach表現の局所解析的ベクトルのなす空間へのLie環の作用からHodge-Tate重みが取り出せるというのが主結果で，Hodge-Tate表現の場合の局所代数的ベクトルについてのColmezの結果の解析的類似になっています．

#### 数理人口学・数理生物学セミナー

14:55-16:40   数理科学研究科棟(駒場) 128演習室号室

ウイルス感染に伴う時間遅れと保存量の存在：ウイルスダイナミクスの立場から (JAPANESE)
[ 講演概要 ]

### 2015年06月16日(火)

#### トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea : 16:30-17:00 Common Room

Stable maps and branched shadows of 3-manifolds (JAPANESE)
[ 講演概要 ]
We study what kind of stable map to the real plane a 3-manifold has. It
is known by O. Saeki that there exists a stable map without certain
singular fibers if and only if the 3-manifold is a graph manifold. According to
F. Costantino and D. Thurston, we identify the Stein factorization of a
stable map with a shadow of the 3-manifold under some modification,
where the above singular fibers correspond to the vertices of the shadow. We
define the notion of stable map complexity by counting the number of
such singular fibers and prove that this equals the branched shadow
complexity. With this equality, we give an estimation of the Gromov norm of the
3-manifold by the stable map complexity. This is a joint work with Yuya Koda.

### 2015年06月15日(月)

#### 代数幾何学セミナー

15:30-17:00   数理科学研究科棟(駒場) 122号室
Christopher Hacon 氏 (University of Utah/RIMS)
Boundedness of the KSBA functor of
SLC models (English)
[ 講演概要 ]
Let $X$ be a canonically polarized smooth $n$-dimensional projective variety over $\mathbb C$ (so that $\omega _X$ is ample), then it is well-known that a fixed multiple of the canonical line bundle defines an embedding of $X$ in projective space. It then follows easily that if we fix certain invariants of $X$, then $X$ belongs to finitely many deformation types. Since canonical models are rarely smooth, it is important to generalize this result to canonically polarized $n$-dimensional projectivevarieties with canonical singularities. Moreover, since these varieties specialize to non-normal varieties it is also important to generalize this result to semi-log canonical pairs. In this talk we will explain a strong version of the above result that applies to semi-log canonical pairs.This is joint work with C. Xu and J. McKernan
[ 講演参考URL ]
http://www.math.utah.edu/~hacon/

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 126号室

The Lyapunov-Schmidt reduction for the CR Yamabe equation on the Heisenberg group (Japanese)
[ 講演概要 ]
We will study CR Yamabe equation for a CR structure on the Heisenberg group which is deformed from the standard structure. By using Lyapunov-Schmidt reduction, it is shown that the perturbation of the standard CR Yamabe solution is a solution to the deformed CR Yamabe equation, under certain conditions of the deformation.

#### 東京確率論セミナー

16:50-18:20   数理科学研究科棟(駒場) 128号室

ランダム媒質中の多次元拡散家庭の再帰性・非再帰性について
(田村要造氏，楠岡誠一郎氏との共同研究)