過去の記録

2013年04月11日(木)

幾何コロキウム

10:00-11:30   数理科学研究科棟(駒場) 122号室

Jeff Viaclovsky 氏 (University of Wisconsin)
Critical metrics on connected sums of Einstein four-manifolds (ENGLISH)
[ 講演概要 ]
I will discuss a gluing procedure designed to obtain critical metrics of quadratic Riemannian functionals on connected sums of certain Einstein four-manifolds. Start with two Einstein four-manifolds of positive scalar curvature which are "rigid". Using the Green's function for the conformal Laplacian, convert one of these into an asymptotically flat (AF) scalar-flat metric. A "naive" approximate critical metric is obtained by identifying the boundary of a large ball in the AF metric with the boundary of a small ball in the other compact Einstein metric, using cutoff functions to glue together the AF metric with a suitably scaled compact metric in order to obtain a smooth metric on the connected sum. It turns out that this naive approximate metric is too rough, and must be refined in order to compute the leading term of the Kuranishi map. The main application is an existence result using two well-known Einstein manifolds as building blocks: the Fubini-Study metric on $¥mathbb{CP}^2$ and the product metric on $S^2 ¥times S^2$. Using these factors in various gluing configurations, a zero of the Kuranishi map is then found for a specific quadratic Riemannian functional on certain connected sums. The exact functional depends on the geometry of the factors, and also on the mass of the AF metric. Using certain quotients of $S^2 ¥times S^2$ as one of the gluing factors, several non-simply connected examples are also obtained. This is joint work with Matt Gursky.

2013年04月10日(水)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 118号室

On nuclearity of $C^*$-algebras associated with Fell bundles over \\'etale groupoids (ENGLISH)

代数学コロキウム

17:30-18:30   数理科学研究科棟(駒場) 056号室
Deepam Patel 氏 (University of Amsterdam)
Motivic structure on higher homotopy of non-nilpotent spaces (ENGLISH)
[ 講演概要 ]
In his fundamental paper on the projective line minus three points, Deligne constructed certain extensions of mixed Tate motives arising from the fundamental group of the projective line minus three points. Since then, motivic structures on homotopy groups have been studied by many authors. In this talk, we will construct a motivic structure on the (nilpotent completion of) n-th homotopy group of P^{n} minus n+2 hyperplanes in general position.

(本講演は「東京北京パリ数論幾何セミナー」として、インターネットによる東大数理, Morningside Center of MathematicsとIHESの双方向同時中継で行います.)

2013年04月09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

[ 講演概要 ]

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

A characterization of non-tube type Hermitian symmetric spaces by visible actions
(JAPANESE)
[ 講演概要 ]
We consider a non-symmetric complex Stein manifold D
which is realized as a line bundle over the complexification of a non-compact irreducible Hermitian symmetric space G/K.

In this talk, we will explain that the compact group action on D is strongly visible in the sense of Toshiyuki Kobayashi if and only if G/K is of non-tube type.
In particular, we focus on our construction of slice which meets every orbit in D from the viewpoint of group theory, namely,
we find an A-part of a generalized Cartan decomposition for homogeneous space D.

We note that our choice of A-part is an abelian.

2013年04月08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

ケーラー・アインシュタイン計量と K 安定性 (JAPANESE)
[ 講演概要 ]
ケーラー・アインシュタイン計量の存在と K 安定性の同値性に関する Chen-Donaldson-Sun, Tian の証明の概略を解説する.

2013年04月02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

Zuckerman導来関手加群の離散的分岐則 (JAPANESE)
[ 講演概要 ]
We consider the restriction of Zuckerman's derived functor modules with respect to symmetric pairs of real reductive groups. When they are discretely decomposable, explicit formulas for the branching laws are obtained by using a realization as D-module on the flag variety and the generalized BGG resolution. In this talk we would like to illustrate how to derive the formulas with a few examples.

2013年03月30日(土)

東京無限可積分系セミナー

13:30-15:30   数理科学研究科棟(駒場) 002号室
Simon Wood 氏 (Kavli IPMU)
On the extended algebra of type sl_2 at positive rational level (ENGLISH)
[ 講演概要 ]
I will be presenting my recent work with Akihiro Tsuchiya
(arXiv:1302.6435).
I will explain how to construct a certain VOA called the "extended
algebra of type sl_2 at positive rational level"
as a subVOA of a lattice VOA, by means of screening operators. I will
then show that this VOA carries a kind of exterior sl_2 action and then
show how one can compute the structure Zhu's algebra and the Poisson
algebra as well as classify all simple modules by using the screening
operators and the sl_2 action. Important concepts such as screening
operators or Zhu's algebra and the Poisson algebra of a VOA will be
reviewed in the talk.

2013年03月19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) 002号室
Tea: 16:00 - 16:30 コモンルーム

Open book foliation and application to contact topology (ENGLISH)
[ 講演概要 ]
Open book foliation is a generalization of Birman and Menasco's braid foliation. Any 3-manifold admits open book decompositions. Open book foliation is a singular foliation on an embedded surface, and is define by the intersection of a surface and the pages of the open book decomposition. By Giroux's identification of open books and contact structures one can use open book foliation method to study contact structures. In this talk I define the open book foliation and show some applications to contact topology. This is joint work with Tetsuya Ito (University of British Columbia).

2013年03月18日(月)

作用素環セミナー

16:00-17:30   数理科学研究科棟(駒場) 118号室

Ultraproducts of von Neumann algebras (JAPANESE)

談話会・数理科学講演会

15:00-17:30   数理科学研究科棟(駒場) 050号室

お茶&Coffee&お菓子: 16:00～16:30 (大講義室ロビー)。

[ 講演概要 ]

[ 講演概要 ]

2013年03月15日(金)

作用素環セミナー

15:45-18:00   数理科学研究科棟(駒場) 118号室
Lucio Cirio 氏 (Univ. M\"unster) 15:45-16:45
Infinitesimal 2-Yang-Baxter operators from a categorification
of the Knizhnik-Zamolodchikov connection (ENGLISH)
Sutanu Roy 氏 (Univ. G\"ottingen) 17:00-18:00
Twisted tensor product of $C^*$-algebras (ENGLISH)

数値解析セミナー

10:00-12:15   数理科学研究科棟(駒場) 056号室

http://www.ms.u-tokyo.ac.jp/gcoe/index.html

Irene Vignon-Clementel 氏 (INRIA Paris Rocquencourt )
Complex flow at the boundaries of branched models: numerical aspects (ENGLISH)
[ 講演参考URL ]
http://www.infsup.jp/utnas/

作用素環セミナー

14:30-15:30   数理科学研究科棟(駒場) 118号室
Stefano Rossi 氏 (Univ. Roma II)
The connected component of a compact quantum group (ENGLISH)

作用素環セミナー

13:15-14:15   数理科学研究科棟(駒場) 118号室
Jean Roydor 氏 (Univ. Bordeaux)
Two Amir-Cambern type theorems for $C^*$-algebras (ENGLISH)

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 128号室

Caterina Zeppieri 氏 (Universität Münster)
Geometric rigidity for incompatible fields and an application to strain-gradient plasticity (ENGLISH)
[ 講演概要 ]
Motivated by the study of nonlinear plane elasticity in presence of edge dislocations, in this talk we show that in dimension two the Friesecke, James, and Müller Rigidity Estimate holds true also for matrix-fields with nonzero curl, modulo an error depending on the total mass of the curl.
The above generalised rigidity is then used to derive a strain-gradient model for plasticity from semi-discrete nonlinear dislocation energies by Gamma-convergence.
The above results are obtained in collaboration with S. Müller (University of Bonn, Germany) and L. Scardia (University of Glasgow, UK).

2013年03月11日(月)

作用素環セミナー

09:45-12:00   数理科学研究科棟(駒場) 123号室
Tristan Bice 氏 (York Univ.) 09:45-10:45
Traces and Ultrapowers (ENGLISH)
David Penneys 氏 (Univ. Toronto) 11:00-12:00
Constructing subfactors with jellyfish (ENGLISH)

作用素環セミナー

13:30-18:15   数理科学研究科棟(駒場) 123号室
Danny Hey 氏 (Univ. Toronto) 13:30-14:30
Classification and the Toms-Winter Conjecture (ENGLISH)
Stephen Curran 氏 (UCLA) 14:45-15:45
Free probability and planar algebras (ENGLISH)
Rasmus Bentmann 氏 (Univ. Copenhagen) 16:00-17:00
Kirchberg $X$-algebras with real rank zero and intermediate cancellation (ENGLISH)
Luis Santiago-Moreno 氏 (Univ. Oregon) 17:15-18:15
Classifying $C^*$-algebras up to W-stability (ENGLISH)

GCOEセミナー

14:45-15:45   数理科学研究科棟(駒場) 123号室
このセミナーはMiniworkshop on Operator Algebras IVの一環として行われます
Stephen Curran 氏 (UCLA)
Free probability and planar algebras (ENGLISH)
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-4.htm

2013年03月08日(金)

FMSPレクチャーズ

10:30-12:00   数理科学研究科棟(駒場) 056号室
Benjamin Burton 氏 (The University of Queensland, Australia)
Knots, algorithms and linear programming: the quest to solve unknot recognition in polynomial time (ENGLISH)
[ 講演概要 ]
In this talk we explore new approaches to the old and difficult computational problem of unknot recognition. Although the best known algorithms for this problem run in exponential time, there is increasing evidence that a polynomial time solution might be possible. We outline several promising approaches, in which computational geometry, linear programming and greedy algorithms all play starring roles. We finish with a new algorithm that combines techniques from topology and combinatorial optimisation, which is the first to exhibit "real world" polynomial time behaviour: although it is still exponential time in theory, exhaustive experimentation shows that this algorithm can solve unknot recognition for "practical" inputs by running just a linear number of linear programs.

This is joint work with Melih Ozlen.

2013年03月07日(木)

統計数学セミナー

14:50-16:00   数理科学研究科棟(駒場) 006号室

[ 講演概要 ]

[ 講演参考URL ]
http://www.sigmath.es.osaka-u.ac.jp/~kamatani/statseminar/2012/16.html

2013年03月06日(水)

講演会

16:00-17:30   数理科学研究科棟(駒場) 117号室
Frederic Le Roux 氏 (Institut de Mathematiques de Jussieu, Universite Pierre et Marie Curie)
The rotation set around a fixed point for surface homeomorphisms. (ENGLISH)
[ 講演概要 ]
We propose two definitions of a local rotation set. As applications, one
gets some criteria for the existence of periodic orbits, and a clear
explanation of Gambaudo-Le Calvez-Pecou's version of the Naishul theorem:
for surface diffeomorphisms, the rotation number of the derivative at a
fixed point which is not a sink nor a source is a topological invariant.
Tha local rotation set also provide an unexpected topological
characterization for the parabolic fixed points of holomorphic maps.

2013年03月05日(火)

統計数学セミナー

14:50-16:00   数理科学研究科棟(駒場) 006号室

ベイズ予測に基いた波動関数の推定と純粋状態モデルの無情報事前分布 (JAPANESE)
[ 講演概要 ]

[ 講演参考URL ]
http://www.sigmath.es.osaka-u.ac.jp/~kamatani/statseminar/2012/15.html

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
Oleg Emanouilov 氏 (Colorado State University)
Uniqueness for inverse boundary value problems by Dirichlet-to
-Neumann map on subboundaries (ENGLISH)
[ 講演概要 ]
We consider inverse boundary value problems for elliptic equations of second order and survey recent results on the uniqueness mainly by partial boundary data. In particular, in two dimensions, we show uniqueness results by means of Dirichlet data supported on an arbitrary subboundary $\\widetilde\\Gamma$ and Neumann data measured on $\\widetilde\\Gamma$. We describe the key idea for the proof: complex geometric optics solutions which are constructed by a Carleman estimate. Also we show the uniqueness by Dirichlet-to-Neumann map on subboundaries in three dimensions.

2013年03月04日(月)

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
M.I. Tribelsky 氏 (Landau Institute)
Resonant Light Scattering by Small Particles (ENGLISH)
[ 講演概要 ]
The problem of light scattering by a small spherical particle is studied within the framework of the exact solution of the Maxwell equations. It is shown that if imaginary part of the dielectric permittivity of the particle is small enough, the problem exhibits sharp giant resonances with very unusual properties. Specifically, the characteristic values of the electric and magnetic fields inside the particle and in its immediate vicinity are singular in the particle size. In non-dissipative case these quantities do not have definite limits when the radius of the particle tends to zero. The field of the Poynting vector in the immediate vicinity of the particle includes singular points, whose number, types and positions are very sensitive to the changes in the incident light frequency. As an example a bifurcation diagram, describing the behavior of the singular points in the vicinity of the dipole resonance for a particle with a certain fixed size is discussed.