## 過去の記録

### 2008年06月05日(木)

#### 作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室

Another analogue of the Borel-Weil theory on loop groups

#### 応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 002号室

Keller-Segel系に対する離散化手法
[ 講演概要 ]

### 2008年06月04日(水)

#### 代数学コロキウム

16:30-17:30   数理科学研究科棟(駒場) 117号室

$p$-adic elliptic polylogarithm, $p$-adic Eisenstein series and Katz measure
(joint work with G. Kings)

[ 講演概要 ]
The Eisenstein classes are important elements in the motivic cohomology
of a modular curve, defined as the specializations of the motivic elliptic
polylogarithm by torsion sections. The syntomic Eisenstein classes are
defined as the image by the syntomic regulator of the motivic Eisenstein
classes. In this talk, we explain our result concerning the relation between
syntomic Eisenstein classes restricted to the ordinary locus and

#### PDE実解析研究会

16:00-18:15   数理科学研究科棟(駒場) 056号室
William Rundell 氏 (Department of Mathematics, Texas A&M University) 16:00-17:00
Inverse Obstacle Recovery when the boundary condition is also unknown
[ 講演概要 ]
We consider the inverse problem of recovering the shape, location
and surface properties of an object where the surrounding medium
is both conductive and homogeneous. It is assumed that the physical situation is modeled by either harmonic functions or solutions of the Helmholtz equation and that the boundary condition on the obstacle is one of impedance type. We measure either Cauchy data, on an accessible part of the exterior boundary or the far field pattern resulting from a plane wave. Given sets of Cauchy data pairs we wish to recover both the shape and location of the unknown obstacle together with its impedance.
It turns out this adds considerable complexity to the analysis. We give a local injectivity result and use two different algorithms
to investigate numerical reconstructions. The setting is in two space dimensions, but indications of possible extensions (and difficulties) to three dimensions are provided. We also look at the case of a nonlinear impedance function.
David Colton 氏 (Department of Mathematical Sciences, University of Delaware) 17:15-18:15
The Inverse Scattering Problem for an Isotropic Medium
[ 講演概要 ]
This talk is concerned with the inverse electromagnetic scattering problem for an isotropic inhomogeneous infinite cylinder. After formulating the direct scattering problem we proceed to the inverse scattering problem which is the main theme of this lecture. After discussing what is known about uniqueness for the inverse problem,we will proceed to the definition and properties of the far field operator. This leads to the study of a rather unusual spectral problem for partial differential equations called the interior transmission problem. We will state what is known about this problem including its role in determining lower bounds for the index of refraction from a knowledge of the far field pattern of the scattered wave, The talk is concluded by briefly considering the case of limited aperture data,in particular the use of the gap reciprocity method to determine the shape and location of buried objects. Numerical examples will be given as well as a number of open problems.

### 2008年06月03日(火)

#### Lie群論・表現論セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室

Matrix valued commuting differential operators with B2 symmetry
[ 講演概要 ]
B2 型のWeyl群の作用による対称性を持つ2次正方行列値の2階の可換な微分作用素を構成した。

[ 講演参考URL ]
http://akagi.ms.u-tokyo.ac.jp/seminar.html

#### トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム

On the geometry of certain slices of the character variety of a knot group
[ 講演概要 ]
joint work with Fumikazu Nagasato (Meijo University)
This talk is concerned with certain subsets in the character variety of a knot group.
These subsets are called '"slices", which are defined as a level set of a regular function associated to a meridian of a knot.
They are related to character varieties for branched covers along the knot.
Some investigations indicate that an equivariant theory for a knot is connected to a theory for branched covers via slices, for example, the equivariant signature of a knot and the equivariant Casson invariant.
In this talk, we will construct a map from slices into the character varieties for branched covers and investigate the properties.
In particular, we focus on slices called "trace-free", which are used to define the Casson-Lin invariant, and the relation to the character variety for two--fold branched cover.

### 2008年06月02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) 128号室

A new series of compact minitwistor spaces and Moishezon twistor spaces over them

#### Kavli IPMU Komaba Seminar

17:00-18:30   数理科学研究科棟(駒場) 002号室
Shinobu Hikami 氏 (The University of Tokyo)
Intersection theory from duality and replica
[ 講演概要 ]
Kontsevich's work on Airy matrix integrals has led to explicit results for the
intersection numbers of the moduli space of curves. In this article we show that a duality between k-point functions on N by N matrices and N-point functions of k by k matrices, plus the replica method, familiar in the theory of disordered systems, allows one to recover Kontsevich's results on the intersection numbers, and to generalize them to other models. This provides an alternative and simple way to compute intersection numbers with one marked point, and leads also to some new results. This is a joint work with E. Brezin (Comm.Math. Phys. in press, arXiv:0708.2210).

### 2008年05月29日(木)

#### 作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Rolf Dyre Svegstrup 氏 (東大数理)
2D models in AQFT from wedge algebras

### 2008年05月27日(火)

#### Lie群論・表現論セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室

Visible actions on multiplicity-free spaces
[ 講演概要 ]
The holomorphic action of a Lie group G on a complex manifold D is called strongly visible if there exist a real submanifold S such that D':=G・S is open in D and an anti-holomorphic diffeomorphism σ which is an identity map on S and preserves each G-orbit in D'.
In this talk, we treat the case where D is a multiplicity-free space V of a connected complex reductive Lie group G(C), and show that the action of a compact real form of G(C) on V is strongly visible.
[ 講演参考URL ]
http://akagi.ms.u-tokyo.ac.jp/seminar.html

### 2008年05月26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) 128号室

### 2008年05月24日(土)

#### 保型形式の整数論月例セミナー

13:30-16:00   数理科学研究科棟(駒場) 123号室
Raimandus Vidunas
(神戸大学理学部
) 13:30-14:30
Identities between Appell's and univariate hyeprgeometric functions

[ 講演概要 ]
We look for univariate specializations of Appell'd bivariante hypergeometric functions that can be expressed in terms of univaraite ${}_{i+1} F_{i} ~(i=1,2,3)$ HGF's. The method is identifying cases when the partial differential equations for Appell's functions imply hypegeometric ordinary differential equations for their univariate specializations. In general, ordinary differential equations for univariate specializations of Apell's functions have order at moast 4.

Whittaker functions with one-dimensional $K$-type on a semisimple Lie group of Hermitian type
[ 講演概要 ]

### 2008年05月23日(金)

#### 談話会・数理科学講演会

16:30-17:30   数理科学研究科棟(駒場) 123号室
お茶&Coffee&お菓子: 16:00～16:30 (コモンルーム)
Jean-Michel Bismut 氏 (Univ. Paris-Sud, Orsay)
Functional integration and index theory

[ 講演概要 ]
The heat equation proof of the Atiyah-Singer index theorem involves a local fantastic cancellation' mechanism, which has long been unexplained conceptually.

In this lecture, I will show how the supersymmetric formalism introduced by physicists has ultimately led to a new understanding of this cancellation mechanism. Ideas of Witten and Atiyah relating the index theorem to the localization formulas of Duistermaat-Heckman in equivariant cohomology have ultimately led to a renewed understanding of the cancellation mechanism as being of geometric nature (albeit in infinite dimensions). The key fact is that when interpreting the heat equation method for the proof of the index theorem, integrals of measures on the loop space of the given manifold, which one obtains via Ito stochastic calculus, should be properly interpreted as integrals of differential forms on the loop space.

I will then explain how this new understanding of the local index theorem has naturally led to a better understanding of spectral invariants, and often to the proof of certain key properties.

### 2008年05月22日(木)

#### 応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 002号室

[ 講演概要 ]

#### 統計数学セミナー

16:20-17:30   数理科学研究科棟(駒場) 126号室

[ 講演概要 ]
メタアナリシスとは、目的を同じくする複数の研究から得られる統計的結果を統合し、より強い統計的 エビデンスを得るための統計解析のことで、近年特に、医学・健康科学の分野において盛んに行われて いる。しかしながら、メタアナリシスのために行われる研究結果の選択過程は、必ずしも無作為(ランダ ム)であるとは限らない。例えば、統計的に有意でない結果は有意である結果に比べて公表(出版)されに くいので、公表されている結果だけでメタアナリシスを行うと統合結果も有意になる、ということがしば しば起こる。研究結果を選択する過程で入り込むバイアスの原因はこの他にもいろいろあり得るが、この 問題は一般に「出版バイアス(publication bias)」の問題と呼ばれている。出版バイアスを調整するた めによく使われる一つの方法は、研究結果の選択のされ方を統計的にモデリングすることであるが、そ のためには研究の選択過程に対して、データそのものからは検証できない強い仮定が必要である。その ため、その仮定がデータ以外の背景情報から強く支持されないと、間違った結論を導く可能性がある。 そこで本講演では、できるだけ多くの場合に許容されるような弱い仮定の下で、(メタアナリシスの結 果としての)信頼区間やP-値の最悪評価を行い、それらにもとづいて最終的な統計的有意性の判断を行 う方法を提案する。この信頼区間やP-値の最悪評価は、選択されなかった研究の数という未知数にも 依存しているので一意には決まらないが、この値を現実的に可能性のある範囲で振らせることによって、 どの辺で統計的有意性に関する結論が変化するかを知ることができる。その意味で、提案する方法は感 度解析法となっている。この方法論は、選択関数の作るある関数空間上の最適化問題の結果にもとづい ているが、今回はその数理的部分についてもできる限り詳しくお話しする予定である。
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2008/02.html

### 2008年05月21日(水)

#### 数理ファイナンスセミナー

17:30-19:00   数理科学研究科棟(駒場) 128号室

Robust Exponential Hedging and Indifference Valuation

### 2008年05月20日(火)

#### 解析学火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 128号室
Vania Sordoni 氏 (ボローニャ大学)
Wave operators for diatomic molecules

#### 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: 16:40 -- 17:00 コモンルーム
Jer\^ome Petit 氏 (東京工業大学, JSPS)
Turaev-Viro TQFT splitting.
[ 講演概要 ]
The Turaev-Viro invariant is a 3-manifolds invariant. It is obtained in this way :
1) we use a combinatorial description of 3-manifolds, in this case it is : triangulation / Pachner moves
2) we define a scalar thanks to a categorical data (spherical category) and a topological data (triangulation)
3)we verify that the scalar is invariant under Pachner moves, then we obtain a 3-manifolds invariant.

The Turaev-Viro invariant can also be extended to a TQFT. Roughly speaking a TQFT is a data which assigns a finite dimensional vector space to every closed surface and a linear application to every 3-manifold with boundary.

In this talk, we will give a decomposition of the Turaev-Viro TQFT. More precisely, we decompose it into blocks. These blocks are given by a group associated to the spherical category which was used to construct the Turaev-Viro invariant. We will show that these blocks define a HQFT (roughly speaking a TQFT with an "homotopical data"). This HQFT is obtained from an homotopical invariant, which is the homotopical version of the Turaev-Viro invariant. Moreover this invariant can be used to obtain the homological Turaev-Viro invariant defined by Yetter.

#### Lie群論・表現論セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室

Lipsman予想の反例と代数多様体の特異点について
[ 講演概要 ]
リー群$G$が多様体$M$に作用しているとき, その商空間$G\\backspace M$のハウスドルフ性は, 不連続群論の研究において重要である. 特に, ベキ零リー群が線型空間にアファインかつ自由に作用するとき, 商位相は常にハウスドルフであるとLipsmanは予想した.
しかし, この予想には反例があり, 商位相は必ずしもハウスドルフでない.
この講演では, この非ハウスドルフ性を可視化'したい. より正確には, $M$への$G$作用から, 自然に代数多様体$V$が定義され, $V$の特異点が商位相の非ハウスドルフ性に対応することを見る.
[ 講演参考URL ]
http://akagi.ms.u-tokyo.ac.jp/seminar.html

### 2008年05月19日(月)

#### Kavli IPMU Komaba Seminar

17:00-18:30   数理科学研究科棟(駒場) 002号室
Jean-Michel Bismut 氏 (Univ. Paris-Sud, Orsay)
A survey of Quillen metrics

[ 講演概要 ]
In this lecture, I will survey basic results
on Quillen metrics.

Indeed let $X$ be a complex K\\"ahler manifold, and let $E$ be a
holomorphic Hermitian vector bundle on $X$. Let $\\lambda$ be the complex line
which is the determinant of the cohomology of $E$. The Quillen metric
is a metric on the line $\\lambda$, which one obtains using a spectral
invariant of the Hodge Laplacian, the Ray-Singer analytic torsion.

The Quillen metrics have a number of remarkable properties. Among them
the curvature theorem says that when one considers a family of such
$X$, the curvature of the holomorphic Hermitian connection on
$\\lambda$ is given by a formula of Riemann-Roch-Grothendieck type.

I will explain some of the ideas which go into the proof of these
properties, which includes Quillen's superconnections.

#### 複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室

On the projectively embeddable complex-foliated structures

#### 講演会

16:00-17:30   数理科学研究科棟(駒場) 126号室
Jean-Pierre Puel 氏
(ヴェルサイユ大学 (Universite de Versailles St Quentin)
)
A non standard unique continuation property related to Schiffer conjecture
[ 講演概要 ]
Coming from a control problem for a coupled fluid-structure system, we are confronted to the following problem in dimension 2:
\\Delta^2 w = -\\lambda \\Delta w in \\Omega w = {\\partial w}/{\\partial n} = 0 on \\Gamma {\\partial\\Delta w}/{\\partial n}=0 on \\Gamma_0 \\subset \\Gamma.
The question is : do we have w=0?
There is a counterexample when \\Omega is a disc. The analogous of (local) Schiffer's conjecture is : is the disc the only domain for which we can have a non zero solution?
Notice that the term local means that the additional boundary condition occurs only on a part of the boundary and when this boundary is not analytic, this is a major difference. A sub-conjecture would be : when the boundary is not analytic, do we have w=0?
Here we show that when \\Omega has a corner of angle \\theta_{0} with \\theta_{0} \\neq \\pi, 3\\pi/2 and when $\\Gamma_{0}$ is (locally) one edge of this angle then the only solution is w=0.
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/top/general-access.html

### 2008年05月15日(木)

#### 作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Mikael Pichot 氏 (東大数理)
Property RD and CAT(0) geometry

#### 応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 002号室

( Stability and uniqueness for surfaces with constant anisotropic mean curvature)
[ 講演概要 ]

を保つ変分に対する非等方的表面エネルギーの臨界点を非等方的平均曲率一定曲

あるときをいう.したがって,エネルギー極小解は安定である.

### 2008年05月13日(火)

#### トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
Tamas Kalman 氏 (東京大学大学院数理科学研究科, JSPS)
The problem of maximum Thurston--Bennequin number for knots
[ 講演概要 ]
Legendrian submanifolds of contact 3-manifolds are
one-dimensional, just like knots. This coincidence'' gives rise to an
interesting and expanding intersection of contact and symplectic geometry
on the one hand and classical knot theory on the other. As an
illustration, we will survey recent results on maximizing the
Thurston--Bennequin number (which is a measure of the twisting of the
contact structure along a Legendrian) within a smooth knot type. In
particular, we will show how Kauffman's state circles can be used to solve
the maximization problem for so-called +adequate (among them, alternating