## Seminar information archive

#### Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Marcus Werner (Kavli IPMU)
Topology in Gravitational Lensing (ENGLISH)
[ Abstract ]
General relativity implies that light is deflected by masses
due to the curvature of spacetime. The ensuing gravitational
lensing effect is an important tool in modern astronomy, and
topology plays a significant role in its properties. In this
talk, I will review topological aspects of gravitational lensing
theory: the connection of image numbers with Morse theory; the
interpretation of certain invariant sums of the signed image
magnification in terms of Lefschetz fixed point theory; and,
finally, a new partially topological perspective on gravitational
light deflection that emerges from the concept of optical geometry
and applications of the Gauss-Bonnet theorem.

### 2012/07/09

#### Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Tomoyuki Hisamoto (Univ. of Tokyo)
Volume of graded linear series and the existence problem of constant scalar curvature Kaehler metric (JAPANESE)
[ Abstract ]
We describe the volume of a graded linear series by the Monge-Ampere mass of the associated equilibrium metric. We relate this formula to the question whether the weak geodesic ray associated to a test configuration of given polarized manifold recovers the Donaldson-Futaki invariant.

### 2012/07/06

#### Colloquium

16:30-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
S.R.Srinivasa Varadhan (Courant Institute of Mathematical Sciences, New York University)
Large Deviations of Random Graphs and Random Matrices (ENGLISH)
[ Abstract ]
A random graph with $n$ vertices is a random symmetric matrix of $0$'s and $1$'s and they share some common aspects in their large deviation behavior. For random matrices it is the question of having large eigenvalues. For random graphs it is having too many or too few subgraph counts, like the number of triangles etc. The question that we will try to answer is what would a random matrix or a random graph conditioned to exhibit such a large deviation look like. Since the randomness is of size $n^2$ large deviation rates of order $n^2$ are possible.

### 2012/07/04

#### Number Theory Seminar

16:40-17:40   Room #056 (Graduate School of Math. Sci. Bldg.)
Patrick Forré (University of Tokyo)
A cohomological Hasse principle of varieties over higher local fields and applications to higher dimensional class field theory (ENGLISH)
[ Abstract ]
In this talk I will give an overview of the necessary tools for a description of the class field theory of varieties over higher local fields developed by sevaral mathematicians. On this I will motivate the importance of the proposal and verification of a cohomological Hasse principle for varieties over higher local fields, a generalization of Kato's conjectures, and sketch the recent progress on this.

#### Classical Analysis

15:30-17:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Hajime Nagoya (Kobe University)
Symmetries of quantum Lax equations for the Painlev\\'e equations (JAPANESE)

### 2012/06/27

#### Classical Analysis

16:00-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Daisuke Yamakawa (Tokyo Institute of Technology)
Moduli space of meromorphic connections with ramified irregular singularities on principal bundles (JAPANESE)

### 2012/06/26

#### Tuesday Seminar of Analysis

16:30-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Kenichi Ito (Division of Mathematics, University of Tsukuba)
Absence of embedded eigenvalues for the Schr\\"odinger operator on manifold with ends (JAPANESE)
[ Abstract ]
We consider a Riemannian manifold with, at least, one expanding end, and prove the absence of $L^2$-eigenvalues for the Schr\\"odinger operator above some critical value. The critical value is computed from the volume growth rate of the end and the potential behavior at infinity. The end structure is formulated abstractly in terms of some convex function, and the examples include asymptotically Euclidean and hyperbolic ends. The proof consists of a priori superexponential decay estimate for eigenfunctions and the absence of superexponentially decaying eigenfunctions, both of which employs the Mourre-type commutator argument. This talk is based on the recent joint work with E.Skibsted (Aarhus University).

### 2012/06/25

#### Algebraic Geometry Seminar

15:30-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Keiji Oguiso (Osaka University)
Automorphism groups of Calabi-Yau manifolds of Picard number two (JAPANESE)
[ Abstract ]
We prove that the automorphism group of an odd dimensional Calabi-Yau manifold of Picard number two is always a finite group. This makes a sharp contrast to the automorphism groups of K3 surfaces and hyperk\\"ahler manifolds and birational automorphism groups, as I shall explain. We also clarify the relation between finiteness of the automorphism group (resp. birational automorphism group) and the rationality of the nef cone (resp. movable cone) for a hyperk\\"ahler manifold of Picard number two. We will also discuss a similar conjectual relation for a Calabi-Yau threefold of Picard number two, together with exsistence of rational curve, expected by the cone conjecture.

#### Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Atsushi Hayashimoto (Nagano National College of Technology)
CR equivalence problem of CR manifolds with slice structure (JAPANESE)

### 2012/06/20

#### Number Theory Seminar

16:40-17:40   Room #056 (Graduate School of Math. Sci. Bldg.)
Kazuki Tokimoto (University of Tokyo)
On the reduction modulo p of representations of a quaternion
division algebra over a p-adic field (JAPANESE)
[ Abstract ]
The p-adic Langlands correspondence and the mod p Langlands correspondence for GL_2(Q_p) are known to be compatible with the reduction modulo p in many cases.
In this talk, we examine whether a similar compatibility exists for the composition of the local Langlands correspondence and the local Jacquet-Langlands correspondence.
The simplest case has already been treated by Vign¥'eras. We deal with more cases.

#### PDE Real Analysis Seminar

10:30-11:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Paolo Maremonti (Seconda Università degli Studi di Napoli)
On the Navier-Stokes Cauchy problem with nondecaying data (ENGLISH)
[ Abstract ]
We prove the well posedeness of the Navier-Stokes Cauchy problem for nondecaying initial data u_0 \\in C (R^n) \\cap L^\\infty (R^n), n >= 3. This problem is studied by Giga, Inui and Matsui for n >= 3, and Giga, Matsui and Sawada in the two dimensional case. The aims of our paper are slight different since we also find pointwise estimates for the pressure field. Via a uniqueness theorem, we give a sort of structure theorem to GIM solutions.

### 2012/06/19

#### Tuesday Seminar on Topology

17:10-18:10   Room #056 (Graduate School of Math. Sci. Bldg.)
Yukio Matsumoto (Gakushuin University)
On the universal degenerating family of Riemann surfaces
over the D-M compactification of moduli space (JAPANESE)
[ Abstract ]
It is usually understood that over the Deligne-
Mumford compactification of moduli space of Riemann surfaces of
genus > 1, there is a family of stable curves. However, if one tries to
construct this family precisely, he/she must first take a disjoint union
of various types of smooth families of stable curves, and then divide
them by their automorphisms to paste them together. In this talk we will
show that once the smooth families are divided, the resulting quotient
family contains not only stable curves but virtually all types of
degeneration of Riemann surfaces, becoming a kind of universal
degenerating family of Riemann surfaces.

#### Numerical Analysis Seminar

16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Hidenori Ogata (The University of Electro-Communications)
Advances in the charge simulation method (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/

### 2012/06/18

#### Algebraic Geometry Seminar

15:30-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Katsutoshi Yamanoi (Tokyo Institute of Technology)
アルバネーゼ次元最大の複素射影多様体の特殊集合について (JAPANESE)
[ Abstract ]
アルバネーゼ次元が最大の複素射影多様体の中に含まれる代数的あるいは超越的な複

#### Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
CR Q-curvature flow and CR Paneitz operator on 3-dimensional CR manifolds (JAPANESE)

#### Lectures

09:45-12:30   Room #002 (Graduate School of Math. Sci. Bldg.)
James Nolen (Duke University) 09:45-10:45
Fluctuation of solutions to PDEs with random coefficients (Part 2) (ENGLISH)
[ Abstract ]
This is continuation of the previous day's lecture.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/
Leonid Ryzhik (Stanford University) 11:00-12:30
Weak coupling limits for particles and PDEs (Part 2) (ENGLISH)
[ Abstract ]
This is continuation of the previous day's lecture.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/

### 2012/06/17

#### Lectures

09:45-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
James Nolen (Duke University) 09:45-17:30
Fluctuation of solutions to PDEs with random coefficients (Part 1) (JAPANESE)
[ Abstract ]
For PDEs with random coefficients, it is interesting to understand whether the solutions exhibit some universal statistical behavior that is independent of the details of the coefficients. In particular, how do solutions fluctuate around the mean behavior? We will discuss this issue in the context of three examples:

(1) Traveling fronts in random media in one dimension.
(2) Elliptic homogenization problems.
(3) Random Hamilton-Jacobi equations.

The relation between PDE tools and probabilistic ideas will be
explained.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/

Leonid Ryzhik (Stanford Univeristy) 13:00-14:45
Weak coupling limits for particles and PDEs (Part 1) (JAPANESE)
[ Abstract ]
Weak random fluctuations in medium parameters may lead to a non-trivial effect after large times and propagation over long distances. We will consider several examples when the large time limit can be treated:

(1) a particle in a weakly random velocity field.
(2) weak random fluctuations of Hamilton equations, and
(3) the linear Scrhoedinger equation with a weak random potential.

The role of long range correlation of the random fluctuations will also be discussed.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/
Gregoire Nadin (CNRS / Paris 6) 15:15-17:15
Asymptotic spreading for heterogeneous Fisher-KPP reaction-diffusion equations (JAPANESE)
[ Abstract ]
The solutions of the heterogeneous Fisher-KPP equation associated with compactly supported initial data are known to take off from the unstable steady state 0 and to converge to the steady state 1 for large times. The aim of this lecture is to estimate the speed at which the interface between 0 and 1 spreads.

Using the new notion of generalized principal eigenvalues for non-compact elliptic operators, we will derive such estimates which will be proved to be optimal for several classes of heterogeneity such as periodic, almost periodic or random stationary ergodic ones.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/

### 2012/06/16

#### Lectures

13:15-17:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Tadahisa Funaki (University of Tokyo) 13:15-14:45
A viewpoint of the stochastic analysis in differential equations (JAPANESE)
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/
Yoshiki Otobe (Shinshu University) 15:00-17:00
Stochastic (partial) differential equations from a functional analytic point of view (JAPANESE)
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~matano/SDE2012/

### 2012/06/14

#### Algebraic Geometry Seminar

13:30-15:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Christian Schnell (IPMU)
Vanishing theorems for perverse sheaves on abelian varieties (ENGLISH)
[ Abstract ]
I will describe a few results, due to Kraemer-Weissauer and myself, about perverse sheaves on complex abelian varieties; they are natural generalizations of the generic vanishing theorem of Green-Lazarsfeld.

### 2012/06/13

#### Number Theory Seminar

16:40-17:40   Room #056 (Graduate School of Math. Sci. Bldg.)
Tomoki Mihara (University of Tokyo)
Singular homologies of non-Archimedean analytic spaces and integrals along cycles (JAPANESE)

#### Lectures

17:00-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Sunder Sethuraman (University of Arizona)
A KPZ equation for zero-range interactions (ENGLISH)
[ Abstract ]
We derive a type of KPZ equation, in terms of a martingale problem, as a scaling limit of fluctuation fields in weakly asymmetric zero-range processes. Joint work (in progress) with Milton Jara and Patricia Goncalves.

#### Lectures

11:00-15:30   Room #128 (Graduate School of Math. Sci. Bldg.)
S. Harase, et. al. (Tokyo Institute of Technology/JSPS)
Workshop for Quasi-Monte Carlo and Pseudo Random Number Generation (ENGLISH)
[ Reference URL ]

### 2012/06/12

#### Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Takefumi Nosaka (RIMS, Kyoto University, JSPS)
Topological interpretation of the quandle cocycle invariants of links (JAPANESE)
[ Abstract ]
Carter et al. introduced many quandle cocycle invariants
combinatorially constructed from link-diagrams. For connected quandles of
finite order, we give a topological meaning of the invariants, without
some torsion parts. Precisely, this invariant equals a sum of "knot
colouring polynomial" and of a Z-equivariant part of the Dijkgraaf-Witten
invariant. Moreover, our approach involves applications to compute "good"
torsion subgroups of the 3-rd quandle homologies and the 2-nd homotopy
groups of rack spaces.

#### Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Toshihisa Kubo (the University of Tokyo)
Conformally invariant systems of differential operators of non-Heisenberg parabolic type (ENGLISH)
[ Abstract ]
The wave operator in Minkowski space is a classical example of a conformally invariant differential operator.
Recently, the notion of conformality of one operator has been
generalized by Barchini-Kable-Zierau to systems of differential operators.
Such systems yield homomrophisms between generalized Verma modules. In this talk we build such systems of second-order differential operators in the maximal non-Heisenberg parabolic setting.
If time permits then we will discuss the corresponding homomorphisms between generalized Verma modules.

#### Lectures

09:50-17:10   Room #118 (Graduate School of Math. Sci. Bldg.)
Josef Dick, et. al. (Univ. New South Wales)
Workshop for Quasi-Monte Carlo and Pseudo Random Number Generation (ENGLISH)
[ Reference URL ]