過去の記録

過去の記録 ~11/11本日 11/12 | 今後の予定 11/13~

代数幾何学セミナー

10:00-12:00   数理科学研究科棟(駒場) 128号室
Dmitry KALEDIN 氏 (Steklov研究所, 東大数理)
Homological methods in non-commutative geometry, part 8

2008年01月07日(月)

諸分野のための数学研究会

13:30-14:30   数理科学研究科棟(駒場) 056号室
伊藤一文 氏 (North Carolina State University)
An Optimal Feedback Solution to Quantum Control Problems.
[ 講演概要 ]
Control of quantum systems described by Schrodinger equation is considered. Feedback control laws are developed for the orbit tracking via a controled Hamiltonian. Asymptotic tracking properties of the feedback laws are analyzed. Numerical integrations via time-splitting are also analyzed and used to demonstrate the feasibility of the proposed feedback laws.
[ 講演参考URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/various/index.html

2008年01月06日(日)

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
青木 貴史 氏 (近畿大理工)
野海・山田方程式系のWKB解に付随する幾何的構造
[ 講演概要 ]
本多尚文氏、梅田陽子氏との共同研究

2007年12月26日(水)

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
Pinhas Grossman 氏 (Vanderbilt University)
Pairs of intermediate subfactors

2007年12月25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
Gregory Eskin 氏 (UCLA)
Inverse boundary value problems for the Schrodinger equation with time-dependent electromagnetic potentials and the Aharonov-Bohm effect
[ 講演概要 ]
We consider the determination of the time-dependent magnetic and electric potentials (modulo gauge transforamtions) by the boundary measurements in domains with obstacles. We use the geometric optics and the tomography of broken rays. The presence of the obstacles leads to the Aharonov-Bohm effect caused by the magnetic and electric fluxes.

2007年12月22日(土)

東京無限可積分系セミナー

13:00-16:30   数理科学研究科棟(駒場) 117号室
池田岳 氏 (岡山理大理) 13:00-14:30
Double Schubert polynomials for the classical Lie groups
[ 講演概要 ]
For each infinite series of the classical Lie groups of type $B$,
$C$ or $D$, we introduce a family of polynomials parametrized by the
elements of the corresponding Weyl group of infinite rank. These
polynomials
represent the Schubert classes in the equivariant cohomology of the
corresponding
flag variety. When indexed by maximal Grassmannian elements of the Weyl
group,
these polynomials are equal to the factorial analogues of Schur $Q$- or
$P$-functions defined earlier by Ivanov. This talk is based on joint work
with L. Mihalcea and H. Naruse.
前野 俊昭 氏 (京大工) 15:00-16:30
Nichols-Woronowicz model of the K-ring of flag vaieties G/B
[ 講演概要 ]
We give a model of the equivariant $K$-ring $K_T(G/B)$ for
generalized flag varieties $G/B$ in the braided Hopf algebra
called Nichols-Woronowicz algebra. Our model is based on
the Chevalley-type formula for $K_T(G/B)$ due to Lenart
and Postnikov, which is described in terms of alcove paths.
We also discuss a conjecture on the model of the quantum
$K$-ring $QK(G/B)$.

2007年12月21日(金)

談話会・数理科学講演会

17:00-18:00   数理科学研究科棟(駒場) 123号室
お茶&Coffee&お菓子: 16:30~17:00 (コモンルーム)
D. Eisenbud 氏 (Univ. of California, Berkeley)
Plato's Cave: what we still don't know about generic projections
[ 講演概要 ]
Riemann Surfaces were first studied algebraically by first projecting them into the complex projective plan; later the same idea was applied to surfaces and higher dimensional varieties, projecting them to hypersurfaces. How much damage is done in this process? For example, what can the fibers of a generic linear projection look like? This is pretty easy for smooth curves and surfaces (though there are still open questions), not so easy in the higher-dimensional case. I'll explain some of what's known, including recent work of mine with Roya Beheshti, Joe Harris, and Craig Huneke.

2007年12月20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
崎山理史 氏 (東大数理)
Gauge-invariant ideal structure of ultragraph $C^*$-algebras

講演会

10:40-12:10   数理科学研究科棟(駒場) 128号室
Mikael Pichot 氏 (東大数理)
Topics in ergodic theory, von Neumann algebras, and rigidity
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/pichot.htm

2007年12月19日(水)

統計数学セミナー

16:20-17:30   数理科学研究科棟(駒場) 122号室
永井 圭二 氏 (横浜国立大学)
Sequential Tests for Criticality of Branching Processes.
[ 講演概要 ]
We consider sequential testing procedures for detection of
criticality of Galton-Watson branching process with or without
immigration. We develop a t-test from fixed accuracy estimation
theory and a sequential probability ratio test (SPRT). We provide
local asymptotic normality (LAN) of the t-test and some asymptotic
optimality of the SPRT. We consider a general framework of
diffusion approximations from discrete-time processes and develop
sequential tests for one-dimensional diffusion processes to
investigate the operating characteristics of sequential tests
of the discrete-time processes. Especially the Bessel process with
constant drift plays a important role for the sequential test
of criticality of branching process with immigration.

(Joint work with K. Hitomi (Kyoto Institute of Technology)
and Y. Nishiyama (Kyoto Univ.))
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2007/13.html

2007年12月18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
R.C. Penner 氏 (USC and Aarhus University)
Groupoid lifts of representations of mapping classes
[ 講演概要 ]
The "Ptolemy groupoid" is the fundamental path groupoid of the dual to the ideal cell decomposition of the decorated Teichmueller space of a punctured or bordered surface, and the "Torelli groupoid" is thesimilar discretization of the fundamental path groupoid of the quotient
by the Torelli subgroup of mapping classes that acts identically on the first integral homology of the surface. Mapping classes can be represented as appropriate elements of the Ptolemy groupoid and likewise for elements of the Torelli group in the Torelli groupoid.

A natural series of questions is to wonder which representations of mapping class groups, Torelli groups, and their subgroups can be lifted to the groupoid level. In a series of joint works with J. Andersen, A. Bene, N. Kawazumi, and S. Morita, we have given explicit lifts of a number of classical representations: The Johnson representations of the classical and higher Torelli groups
and the symplectic representation of the mapping class group all lift to the Torelli groupoid. Furthermore, the Nielsen representation of the mapping class group as automorphisms of a
free group lifts to the Ptolemy groupoid, and hence so too does any representation
of the mapping class group that factors through its action on the fundamental group of
the surface such as the Magnus representation. We shall survey these various groupoid lifts and discuss current and potential future applications.

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
阿部 紀行 氏 (東京大学)
On the existence of homomorphisms between principal series of complex
semisimple Lie groups
[ 講演概要 ]
The principal series representations of a semisimple Lie group play an important role in the representation theory. We study the principal series representation of a complex semisimple Lie group and determine when there exists a nonzero homomorphism between the representations.
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~toshi/seminar/ut-seminar.html

2007年12月17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
寺杣友秀 氏 (東京大学)
種数3の曲線とあるCalabi-Yau threefoldの代数的対応(松本圭司氏との共同研究)

Kavli IPMU Komaba Seminar

17:00-18:30   数理科学研究科棟(駒場) 002号室
Ken-Ichi Yoshikawa 氏 (The University of Tokyo)
Analytic torsion for Calabi-Yau threefolds
[ 講演概要 ]
In 1994, Bershadky-Cecotti-Ooguri-Vafa conjectured that analytic torsion
gives rise to a function on the moduli space of Calabi-Yau threefolds and
that it coincides with the quantity $F_{1}$ in string theory.
Since the holomorphic part of $F_{1}$ is conjecturally the generating function
of the counting problem of elliptic curves in the mirror Calabi-Yau threefold,
this implies the conjectural equivalence of analytic torsion and the counting
problem of elliptic curves for Calabi-Yau threefolds through mirror symmetry.

After Bershadsky-Cecotti-Ooguri-Vafa, we introduced an invariant of
Calabi-Yau threefolds, which we obtained using analytic torsion and
a Bott-Chern secondary class. In this talk, we will talk about the construction
and some explicit formulae of this analytic torsion invariant.
Some part of this talk is based on the joint work with H. Fang and Z. Lu.

2007年12月13日(木)

講演会

10:40-12:10   数理科学研究科棟(駒場) 128号室
Mikael Pichot 氏 (東大数理)
Topics in ergodic theory, von Neumann algebras, and rigidity
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/pichot.htm

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
Danielle Hilhorst 氏 (CNRS / パリ第11大学)
Singular limit of a competition-diffusion system
[ 講演概要 ]
We revisit a competition-diffusion system for the densities of biological populations, and (i) prove the strong convergence in L^2 of the densities of the biological species (joint work with Iida, Mimura and Ninomiya); (ii) derive the singular limit of some reaction terms as the reaction coefficient tends to infinity (joint work with Martin and Mimura).

2007年12月12日(水)

統計数学セミナー

15:20-16:30   数理科学研究科棟(駒場) 122号室
Stefano IACUS 氏 (Department of Economics, Business and Statistics, University of Milan)
Inference problems for the telegraph process observed at discrete times
[ 講演概要 ]
The telegraph process {X(t), t>0}, has been introduced (see
Goldstein, 1951) as an alternative model to the Brownian motion B(t).
This process describes a motion of a particle on the real line which
alternates its velocity, at Poissonian times, from +v to -v. The
density of the distribution of the position of the particle at time t
solves the hyperbolic differential equation called telegraph equation
and hence the name of the process.
Contrary to B(t) the process X(t) has finite variation and
continuous and differentiable paths. At the same time it is
mathematically challenging to handle. Several variation of this
process have been recently introduced in the context of Finance.

In this talk we will discuss pseudo-likelihood and moment type
estimators of the intensity of the Poisson process, from discrete
time observations of standard telegraph process X(t). We also
discuss the problem of change point estimation for the intensity of
the underlying Poisson process and show the performance of this
estimator on real data.
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2007/12.html

2007年12月11日(火)

トポロジー火曜セミナー

16:30-18:40   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
Xavier G\'omez-Mont 氏 (CIMAT, Mexico) 16:30-17:30
A Singular Version of The Poincar\\'e-Hopf Theorem
[ 講演概要 ]
The Poincar\\'e-Hopf Theorem asserts that the Euler Characteristic of a compact manifold is the sum of the indices of any vector field on it with isolated singularities.

A hypersurface in real or complex number space may be considered as the limit of the smooth hypersurfaces obtained from nearby regular values. The singularity contains “hidden” topology, which is unfolded by a smooth regeneration. At the singularity one has an algebraic invariant, the Jacobi Algebra, which is obtained by considering analytic functions modulo the partial derivatives. It contains topological information of the singularity.

One may consider vector fields tangent to a hypersurface with isolated singularities, and define topologically an index, which coincides with the sum of the Poincar\\'e-Hopf indices of a regeneration of it tangent to a nearby smooth hypersurface.

I will explain how to compute the index of a vector field X tangent to an isolated hypersurface singularity V using Homological Algebra, as the Euler Characteristic of the homology of the complex obtained by contracting differential forms on V with the vector field X. The formula contains several terms, but the higher order terms may be translated from the invariants of the singular point to invariants in the Jacobi Algebra, making this translation a local version of the Poincar\\'e-Hopf Theorem.

I will also explain how some of these ideas can be extended to complete intersections.
Miguel A. Xicotencatl 氏 (CINVESTAV, Mexico) 17:40-18:40
Chen Ruan cohomology of cotangent orbifolds and Chas-Sullivan string topology
[ 講演概要 ]
(Joint with: A. Gonzalez, E. Lupercio, C. Segovia, and B. Uribe)

At the end of 90's, two theories of topology were invented roughly at the same time and attracted considerable interest in the mathematical community. One is the Chas-Sullivan's loop product on the homology of loop space and the second one is Chen-Ruan's stringy cohomology of orbifold. It was an observation of Chen that inertia orbifold (which carries Chen-Ruan cohomology) is the space of constant loops of an orbifold. Therefore, two theories should interact. In this work we show that for an interesting family of orbifolds, the virtual orbifold cohomology, turns out to be a subalgebra of the homology of the loop orbifold, and is isomorphic, as algebras, to the Chen-Ruan orbifold cohomology of its cotangent orbifold.

代数幾何学セミナー

10:00-12:00   数理科学研究科棟(駒場) 128号室
次回は2008年1月8日です.
Dmitry KALEDIN 氏 (Steklov研究所, 東大数理)
Homological methods in non-commutative geometry, part 7

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
井上順子 氏 (鳥取大学)
Characterization of some smooth vectors for irreducible representations of exponential solvable Lie groups
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~toshi/seminar/ut-seminar.html

2007年12月10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
杉山健一 氏 (千葉大学)
岩澤予想の幾何学的類似の量子化(予想される結果)

Kavli IPMU Komaba Seminar

17:00-18:30   数理科学研究科棟(駒場) 002号室
Dmitry Kaledin 氏 (Steklov Institute and The University of Tokyo)
Deligne conjecture and the Drinfeld double.
[ 講演概要 ]
Deligne conjecture describes the structure which exists on
the Hochschild cohomology $HH(A)$ of an associative algebra
$A$. Several proofs exists, but they all combinatorial to a certain
extent. I will present another proof which is more categorical in
nature (in particular, the input data are not the algebra $A$, but
rather, the tensor category of $A$-bimodules). Combinatorics is
still there, but now it looks more natural -- in particular, the
action of the Gerstenhaber operad, which is know to consist of
homology of pure braid groups, is induced by the action of the braid
groups themselves on the so-called "Drinfeld double" of the category
$A$-bimod.

If time permits, I will also discuss what additional structures
appear in the Calabi-Yau case, and what one needs to impose to
insure Hodge-to-de Rham degeneration.

2007年12月06日(木)

講演会

10:40-12:10   数理科学研究科棟(駒場) 128号室
Mikael Pichot 氏 (東大数理)
Topics in ergodic theory, von Neumann algebras, and rigidity
[ 講演参考URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/pichot.htm

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 126号室
柳田 英二 氏 (東北大学大学院理学研究科)
藤田型方程式における時間大域解の挙動について
[ 講演概要 ]
この講演では,藤田型の半線形放物型偏微分方程式に関する M. Fila, J. King, P. Polacik, M. Winkler らとの共同研究による成果についてその概要を紹介する.全空間上の藤田型方程式については,これまで様々な挙動を示す時間大域解の存在が示されている.そこで大域解の時間的挙動と初期値の空間的挙動の関係を詳細に調べることにより,大域解をいくつかに分類し,その挙動がそれぞれ異なるメカニズムに支配されていることを明らかにする.時間が許せば,最近の進展や関連する話題についても触れる予定である.

2007年12月05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
中村健太郎 氏 (東京大学大学院数理科学研究科)
Classification of two dimensional trianguline representations of p-adic fields
[ 講演概要 ]
Trianguline representation is a class of p-adic Galois representations of p-adic fields. This was defined by P.Colmez by using ($\\varphi, \\Gamma$)-modules over Robba ring. In his study of p-adic local Langlands correspondence of GL_2(Q_p), he completely classified two dimensional trianguline representations of Q_p. On the other hand, L.Berger recently defined the category of B-pairs and established the equivalence between the category of B-pairs and the category of ($\\varphi,\\Gamma$)-modules over Robba ring. In this talk, we extend the Colmez's result by using B-pairs. We completely classify two dimensional trianguline representations of K for any finite extension of Q_p. We also talk about a relation between two dimensional trianguline representations and principal series or special series of GL_2(K).

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