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Seminar information archive
Seminar information archive ～12/09｜Today's seminar 12/10 | Future seminars 12/11～
2010/10/28
Operator Algebra Seminars
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Makoto Yamashita (Univ. Tokyo)
Type III representations of the infinite symmetric group (ENGLISH)
Makoto Yamashita (Univ. Tokyo)
Type III representations of the infinite symmetric group (ENGLISH)
[ Abstract ]
Based on earlier results about the structure of the II$_1$ representations of the infinite symmetric group, we investigate its type III representations and the related inclusion of von Neumann algebras of type III.
Based on earlier results about the structure of the II$_1$ representations of the infinite symmetric group, we investigate its type III representations and the related inclusion of von Neumann algebras of type III.
Lectures
10:40-12:10 Room #123 (Graduate School of Math. Sci. Bldg.)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
Jean Meyer, Yasuko HISAMATSU (Risk Capital Market Tokyo, BNP Paribas)
Market, Liquidity and Counterparty Risk (ENGLISH)
[ Abstract ]
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
1. Introduction to the market risk
- Introduction to the Risk Management
in the Financial institutions
- Overview of the main market risks
2. Market & Liquidity Risks –Basics
-Presentation of the main Greeks
-Focus on volatility risk
-Focus on correlation risk
-Conclusion (common features of the market risks)
3. Risk measure
- Stress test
- Value at risk
- Risks measure for counterparty risk
2010/10/26
Seminar on Geometric Complex Analysis
13:00-14:30 Room #123 (Graduate School of Math. Sci. Bldg.)
Dan Popovici (Toulouse)
Limits of Moishezon Manifolds under Holomorphic Deformations (ENGLISH)
Dan Popovici (Toulouse)
Limits of Moishezon Manifolds under Holomorphic Deformations (ENGLISH)
[ Abstract ]
We prove that if all the fibres, except one, of a holomorphic family of compact complex manifolds are supposed to be Moishezon (i.e. bimeromorphic to projective manifolds), then the remaining (limit) fibre is again Moishezon. The two ingredients of the proof are the relative Barlet space of divisors contained in the fibres for which we show properness over the base of the family and the "strongly Gauduchon" (sG) metrics that we have introduced for the purpose of controlling volumes of cycles. These new metrics enjoy stability properties under both deformations and modifications and play a crucial role in obtaining a uniform control on volumes of relative divisors that prove the above-mentioned properness.
We prove that if all the fibres, except one, of a holomorphic family of compact complex manifolds are supposed to be Moishezon (i.e. bimeromorphic to projective manifolds), then the remaining (limit) fibre is again Moishezon. The two ingredients of the proof are the relative Barlet space of divisors contained in the fibres for which we show properness over the base of the family and the "strongly Gauduchon" (sG) metrics that we have introduced for the purpose of controlling volumes of cycles. These new metrics enjoy stability properties under both deformations and modifications and play a crucial role in obtaining a uniform control on volumes of relative divisors that prove the above-mentioned properness.
Tuesday Seminar on Topology
17:00-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Kazuo Habiro (RIMS, Kyoto University)
Quantum fundamental groups and quantum representation varieties for 3-manifolds (JAPANESE)
Kazuo Habiro (RIMS, Kyoto University)
Quantum fundamental groups and quantum representation varieties for 3-manifolds (JAPANESE)
[ Abstract ]
We define a refinement of the fundamental groups of 3-manifolds and
a generalization of representation variety of the fundamental group
of 3-manifolds. We consider the category $H$ whose morphisms are
nonnegative integers, where $n$ corresponds to a genus $n$ handlebody
equipped with an embedding of a disc into the boundary, and whose
morphisms are the isotopy classes of embeddings of handlebodies
compatible with the embeddings of the disc into the boundaries. For
each 3-manifold $M$ with an embedding of a disc into the boundary, we
can construct a contravariant functor from $H$ to the category of
sets, where the object $n$ of $H$ is mapped to the set of isotopy
classes of embedding of the genus $n$ handlebody into $M$, compatible
with the embeddings of the disc into the boundaries. This functor can
be regarded as a refinement of the fundamental group of $M$, and we
call it the quantum fundamental group of $M$. Using this invariant, we
can construct for each co-ribbon Hopf algebra $A$ an invariant of
3-manifolds which may be regarded as (the space of regular functions
on) the representation variety of $M$ with respect to $A$.
We define a refinement of the fundamental groups of 3-manifolds and
a generalization of representation variety of the fundamental group
of 3-manifolds. We consider the category $H$ whose morphisms are
nonnegative integers, where $n$ corresponds to a genus $n$ handlebody
equipped with an embedding of a disc into the boundary, and whose
morphisms are the isotopy classes of embeddings of handlebodies
compatible with the embeddings of the disc into the boundaries. For
each 3-manifold $M$ with an embedding of a disc into the boundary, we
can construct a contravariant functor from $H$ to the category of
sets, where the object $n$ of $H$ is mapped to the set of isotopy
classes of embedding of the genus $n$ handlebody into $M$, compatible
with the embeddings of the disc into the boundaries. This functor can
be regarded as a refinement of the fundamental group of $M$, and we
call it the quantum fundamental group of $M$. Using this invariant, we
can construct for each co-ribbon Hopf algebra $A$ an invariant of
3-manifolds which may be regarded as (the space of regular functions
on) the representation variety of $M$ with respect to $A$.
Numerical Analysis Seminar
16:30-18:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Tomoaki Okayama (Hitotsubashi University)
Theoretical analysis of Sinc schemes for integral equations of the second kind (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/
Tomoaki Okayama (Hitotsubashi University)
Theoretical analysis of Sinc schemes for integral equations of the second kind (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/
Lie Groups and Representation Theory
16:30-18:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Daniel Sternheimer (Keio University and Institut de Mathematiques de Bourgogne)
Some instances of the reasonable effectiveness (and limitations) of symmetries and deformations in fundamental physics (ENGLISH)
https://www.ms.u-tokyo.ac.jp/~toshi/seminar/ut-seminar2010.html
Daniel Sternheimer (Keio University and Institut de Mathematiques de Bourgogne)
Some instances of the reasonable effectiveness (and limitations) of symmetries and deformations in fundamental physics (ENGLISH)
[ Abstract ]
In this talk we survey some applications of group theory and deformation theory (including quantization) in mathematical physics. We start with sketching applications of rotation and discrete groups representations in molecular physics (``dynamical" symmetry breaking in crystals, Racah-Flato-Kibler; chains of groups and symmetry breaking). These methods led to the use of ``classification Lie groups" (``internal symmetries") in particle physics. Their relation with space-time symmetries will be discussed. Symmetries are naturally deformed, which eventually brought to Flato's deformation philosophy and the realization that quantization can be viewed as a deformation, including the many avatars of deformation quantization (such as quantum groups and quantized spaces). Nonlinear representations of Lie groups can be viewed as deformations (of their linear part), with applications to covariant nonlinear evolution equations. Combining all these suggests an Ansatz based on Anti de Sitter space-time and group, a deformation of the Poincare group of Minkowski space-time, which could eventually be quantized, with possible implications in particle physics and cosmology. Prospects for future developments between mathematics and physics will be indicated.
[ Reference URL ]In this talk we survey some applications of group theory and deformation theory (including quantization) in mathematical physics. We start with sketching applications of rotation and discrete groups representations in molecular physics (``dynamical" symmetry breaking in crystals, Racah-Flato-Kibler; chains of groups and symmetry breaking). These methods led to the use of ``classification Lie groups" (``internal symmetries") in particle physics. Their relation with space-time symmetries will be discussed. Symmetries are naturally deformed, which eventually brought to Flato's deformation philosophy and the realization that quantization can be viewed as a deformation, including the many avatars of deformation quantization (such as quantum groups and quantized spaces). Nonlinear representations of Lie groups can be viewed as deformations (of their linear part), with applications to covariant nonlinear evolution equations. Combining all these suggests an Ansatz based on Anti de Sitter space-time and group, a deformation of the Poincare group of Minkowski space-time, which could eventually be quantized, with possible implications in particle physics and cosmology. Prospects for future developments between mathematics and physics will be indicated.
https://www.ms.u-tokyo.ac.jp/~toshi/seminar/ut-seminar2010.html
2010/10/21
Operator Algebra Seminars
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Benoit Collins (Univ. Ottawa)
Free probability and entropy additivity problems for Quantum information theory (ENGLISH)
Benoit Collins (Univ. Ottawa)
Free probability and entropy additivity problems for Quantum information theory (ENGLISH)
2010/10/20
Seminar on Mathematics for various disciplines
10:30-11:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Naohisa Ogawa (Hokkaido Institute of Technology)
Curvature Dependent Diffusion Flow on Surface with Thickness (JAPANESE)
Naohisa Ogawa (Hokkaido Institute of Technology)
Curvature Dependent Diffusion Flow on Surface with Thickness (JAPANESE)
[ Abstract ]
Particle diffusion in a two dimensional curved surface with thickness
embedded in $R_3$ is considered.
In addition to the usual diffusion flow, we find a new flow with an explicit
curvature dependence in $\\epsilon$ (thickness of surface) expansion.
As an example, the surface of elliptic cylinder is considered, and curvature
dependent diffusion coefficient is calculated. In addition, we consider the
1 dimensional object in $R_3$ (Tube),
and check the physical meaning of curvature effect.
Particle diffusion in a two dimensional curved surface with thickness
embedded in $R_3$ is considered.
In addition to the usual diffusion flow, we find a new flow with an explicit
curvature dependence in $\\epsilon$ (thickness of surface) expansion.
As an example, the surface of elliptic cylinder is considered, and curvature
dependent diffusion coefficient is calculated. In addition, we consider the
1 dimensional object in $R_3$ (Tube),
and check the physical meaning of curvature effect.
2010/10/19
Tuesday Seminar on Topology
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Jinseok Cho (Waseda University)
Optimistic limits of colored Jones invariants (ENGLISH)
Jinseok Cho (Waseda University)
Optimistic limits of colored Jones invariants (ENGLISH)
[ Abstract ]
Yokota made a wonderful theory on the optimistic limit of Kashaev
invariant of a hyperbolic knot
that the limit determines the hyperbolic volume and the Chern-Simons
invariant of the knot.
Especially, his theory enables us to calculate the volume of a knot
combinatorially from its diagram for many cases.
We will briefly discuss Yokota theory, and then move to the optimistic
limit of colored Jones invariant.
We will explain a parallel version of Yokota theory based on the
optimistic limit of colored Jones invariant.
Especially, we will show the optimistic limit of colored Jones
invariant coincides with that of Kashaev invariant modulo 2\\pi^2.
This implies the optimistic limit of colored Jones invariant also
determines the volume and Chern-Simons invariant of the knot, and
probably more information.
This is a joint-work with Jun Murakami of Waseda University.
Yokota made a wonderful theory on the optimistic limit of Kashaev
invariant of a hyperbolic knot
that the limit determines the hyperbolic volume and the Chern-Simons
invariant of the knot.
Especially, his theory enables us to calculate the volume of a knot
combinatorially from its diagram for many cases.
We will briefly discuss Yokota theory, and then move to the optimistic
limit of colored Jones invariant.
We will explain a parallel version of Yokota theory based on the
optimistic limit of colored Jones invariant.
Especially, we will show the optimistic limit of colored Jones
invariant coincides with that of Kashaev invariant modulo 2\\pi^2.
This implies the optimistic limit of colored Jones invariant also
determines the volume and Chern-Simons invariant of the knot, and
probably more information.
This is a joint-work with Jun Murakami of Waseda University.
2010/10/18
Seminar on Geometric Complex Analysis
10:30-11:30 Room #128 (Graduate School of Math. Sci. Bldg.)
Sergey Ivashkovitch (Univ. de Lille)
Limiting behavior of minimal trajectories of parabolic vector fields on the complex projective plane. (ENGLISH)
Sergey Ivashkovitch (Univ. de Lille)
Limiting behavior of minimal trajectories of parabolic vector fields on the complex projective plane. (ENGLISH)
[ Abstract ]
The classical Poincare-Bendixson theory describes the way a trajectory of a vector field on the real plane behaves when accumulating to the singular locus of the vector field. We shall describe, in the first approximation, the way a minimal trajectory of a parabolic complex polynomial vector field (or, a holomorphic foliation) on the complex projective plane approaches the singular locus. In particular we shall prove that if a holomorphic foliation has an exceptional minimal set then its nef model is necessarily hyperbolic.
The classical Poincare-Bendixson theory describes the way a trajectory of a vector field on the real plane behaves when accumulating to the singular locus of the vector field. We shall describe, in the first approximation, the way a minimal trajectory of a parabolic complex polynomial vector field (or, a holomorphic foliation) on the complex projective plane approaches the singular locus. In particular we shall prove that if a holomorphic foliation has an exceptional minimal set then its nef model is necessarily hyperbolic.
Seminar on Geometric Complex Analysis
13:00-14:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Philippe Eyssidieux (Institut Fourier, Grenoble)
Degenerate complex Monge-Ampere equations (ENGLISH)
Philippe Eyssidieux (Institut Fourier, Grenoble)
Degenerate complex Monge-Ampere equations (ENGLISH)
Kavli IPMU Komaba Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Todor Milanov (IPMU)
Quasi-modular forms and Gromov--Witten theory of elliptic orbifold $\\mathbb{P}^1$ (ENGLISH)
Todor Milanov (IPMU)
Quasi-modular forms and Gromov--Witten theory of elliptic orbifold $\\mathbb{P}^1$ (ENGLISH)
[ Abstract ]
This talk is based on my current work with Y. Ruan. Our project is part of the so called Landau--Ginzburg/Calabi-Yau correspondence. The latter is a conjecture, due to Ruan, that describes the relation between the $W$-spin invariants of a Landau-Ginzburg potential $W$ and the Gromov--Witten invariants of a certain Calabi--Yau orbifold. I am planning first to explain the higher-genus reconstruction formalism of Givental. This formalism together with the work of M. Krawitz and Y. Shen allows us to express the Gromov--Witten invariants of the orbifold $\\mathbb{P}^1$'s with weights $(3,3,3)$, $(2,4,4)$, and $(2,3,6)$ in terms of Saito's Frobenius structure associated with the simple elliptic singularities $P_8$, $X_9$, and $J_{10}$ respectively. After explaining Givental's formalism, my goal would be to discuss the Saito's flat structure, and to explain how its modular behavior fits in the Givental's formalism. This allows us to prove that the Gromov--Witten invariants are quasi-modular forms on an appropriate modular group.
This talk is based on my current work with Y. Ruan. Our project is part of the so called Landau--Ginzburg/Calabi-Yau correspondence. The latter is a conjecture, due to Ruan, that describes the relation between the $W$-spin invariants of a Landau-Ginzburg potential $W$ and the Gromov--Witten invariants of a certain Calabi--Yau orbifold. I am planning first to explain the higher-genus reconstruction formalism of Givental. This formalism together with the work of M. Krawitz and Y. Shen allows us to express the Gromov--Witten invariants of the orbifold $\\mathbb{P}^1$'s with weights $(3,3,3)$, $(2,4,4)$, and $(2,3,6)$ in terms of Saito's Frobenius structure associated with the simple elliptic singularities $P_8$, $X_9$, and $J_{10}$ respectively. After explaining Givental's formalism, my goal would be to discuss the Saito's flat structure, and to explain how its modular behavior fits in the Givental's formalism. This allows us to prove that the Gromov--Witten invariants are quasi-modular forms on an appropriate modular group.
Algebraic Geometry Seminar
16:40-18:10 Room #126 (Graduate School of Math. Sci. Bldg.)
Akiyoshi Sannai (Univ. of Tokyo)
Galois extensions and maps on local cohomology (JAPANESE)
Akiyoshi Sannai (Univ. of Tokyo)
Galois extensions and maps on local cohomology (JAPANESE)
2010/10/14
Operator Algebra Seminars
16:30-18:00 Room #122 (Graduate School of Math. Sci. Bldg.)
Yasuyuki Kawahigashi (Univ. Tokyo)
Nonstandard analysis for operator algebraists (JAPANESE)
Yasuyuki Kawahigashi (Univ. Tokyo)
Nonstandard analysis for operator algebraists (JAPANESE)
2010/10/12
Tuesday Seminar on Topology
16:30-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Andrei Pajitnov (Univ. de Nantes, The University of Tokyo)
Asymptotics of Morse numbers of finite coverings of manifolds (ENGLISH)
Andrei Pajitnov (Univ. de Nantes, The University of Tokyo)
Asymptotics of Morse numbers of finite coverings of manifolds (ENGLISH)
[ Abstract ]
Let X be a closed manifold;
denote by m(X) the Morse number of X
(that is, the minimal number of critical
points of a Morse function on X).
Let Y be a finite covering of X of degree d.
In this survey talk we will address the following question
posed by M. Gromov: What are the asymptotic properties
of m(N) as d goes to infinity?
It turns out that for high-dimensional manifolds with
free abelian fundamental group the asymptotics of
the number m(N)/d is directly related to the Novikov homology
of N. We prove this theorem and discuss related results.
Let X be a closed manifold;
denote by m(X) the Morse number of X
(that is, the minimal number of critical
points of a Morse function on X).
Let Y be a finite covering of X of degree d.
In this survey talk we will address the following question
posed by M. Gromov: What are the asymptotic properties
of m(N) as d goes to infinity?
It turns out that for high-dimensional manifolds with
free abelian fundamental group the asymptotics of
the number m(N)/d is directly related to the Novikov homology
of N. We prove this theorem and discuss related results.
2010/10/08
Colloquium
16:30-17:30 Room #123 (Graduate School of Math. Sci. Bldg.)
Ryu Sasaki (Yukawa Institute for Theoretical Physics, Kyoto University)
Exceptional Jacobi polynomials as solutions of a Schroedinger
(Sturm-Liouville) equation with $3 +¥ell$ ($¥ell=1,2,¥ldots) regular
singularities (JAPANESE)
Ryu Sasaki (Yukawa Institute for Theoretical Physics, Kyoto University)
Exceptional Jacobi polynomials as solutions of a Schroedinger
(Sturm-Liouville) equation with $3 +¥ell$ ($¥ell=1,2,¥ldots) regular
singularities (JAPANESE)
[ Abstract ]
Global solutions of Fuchsian differential equations with more than 3 (hypergeometric) or four (Heun) regular singularities had been virtually unkown. Here I present a complete set of eigenfunctions of a Schroedinger (Sturm-Liouville) equation with $3 + ¥ell$ ($¥ell=1,2,¥ldots$) regular singularities. They are deformations of the Darboux-P¥" oschl-Teller potential with the Hamiltonian (Schroedinger operator) ¥[ ¥mathcal{H}=-¥frac{d^2}{dx^2}+¥frac{g(g-1)}{¥sin^2x}+¥frac{h(h-1)} {¥cos^2x}¥] The eigenfunctions consist of the {¥em exceptional Jacobi polynomials} $¥{P_{¥ell,n}(¥eta)¥}$, $n=0,1,2,¥ldots$, with deg($P_{¥ell,n}$)$=n+¥ell$. Thus the restriction due to Bochner's theorem does not apply. The confluent limit produces two sets of the exceptional Laguerre polynomials for $¥ell=1,2,¥ldots$. Similar deformation method provides the exceptional Wilson and Askey-Wilson polynomials for $¥ell=1,2,¥ldots$.
Global solutions of Fuchsian differential equations with more than 3 (hypergeometric) or four (Heun) regular singularities had been virtually unkown. Here I present a complete set of eigenfunctions of a Schroedinger (Sturm-Liouville) equation with $3 + ¥ell$ ($¥ell=1,2,¥ldots$) regular singularities. They are deformations of the Darboux-P¥" oschl-Teller potential with the Hamiltonian (Schroedinger operator) ¥[ ¥mathcal{H}=-¥frac{d^2}{dx^2}+¥frac{g(g-1)}{¥sin^2x}+¥frac{h(h-1)} {¥cos^2x}¥] The eigenfunctions consist of the {¥em exceptional Jacobi polynomials} $¥{P_{¥ell,n}(¥eta)¥}$, $n=0,1,2,¥ldots$, with deg($P_{¥ell,n}$)$=n+¥ell$. Thus the restriction due to Bochner's theorem does not apply. The confluent limit produces two sets of the exceptional Laguerre polynomials for $¥ell=1,2,¥ldots$. Similar deformation method provides the exceptional Wilson and Askey-Wilson polynomials for $¥ell=1,2,¥ldots$.
2010/10/06
Geometry Seminar
14:45-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Kei Irie (Kyoto Univ.) 14:45-16:15
Handle attaching in wrapped Floer homology and brake orbits in classical Hamiltonian systems (JAPANESE)
Mirror Symmetry for Weighted Homogeneous Polynomials (JAPANESE)
Kei Irie (Kyoto Univ.) 14:45-16:15
Handle attaching in wrapped Floer homology and brake orbits in classical Hamiltonian systems (JAPANESE)
[ Abstract ]
In this talk, the term "classical Hamiltonian systems" means special types of Hamiltonian systems, which describe solutions of classical equations of motion. The study of periodic solutions of Hamiltonian systems is an interesting problem, and for classical Hamiltonian systems, the following result is known : for any compact and regular energy surface $S$, there exists a brake orbit (a particular type of periodic solutions) on $S$. This result is first proved by S.V.Bolotin in 1978, and it is a special case of the Arnold chord conjecture. In this talk, I will explain that calculations of wrapped Floer homology (which is a variant of Lagrangian Floer homology) give a new proof of the above result.
Atsushi Takahashi (Osaka Univ.) 16:30-18:00In this talk, the term "classical Hamiltonian systems" means special types of Hamiltonian systems, which describe solutions of classical equations of motion. The study of periodic solutions of Hamiltonian systems is an interesting problem, and for classical Hamiltonian systems, the following result is known : for any compact and regular energy surface $S$, there exists a brake orbit (a particular type of periodic solutions) on $S$. This result is first proved by S.V.Bolotin in 1978, and it is a special case of the Arnold chord conjecture. In this talk, I will explain that calculations of wrapped Floer homology (which is a variant of Lagrangian Floer homology) give a new proof of the above result.
Mirror Symmetry for Weighted Homogeneous Polynomials (JAPANESE)
[ Abstract ]
First we give an overview of the algebraic and the geometric aspects of the mirror symmetry conjecture for weighted homogeneous polynomials. Then we concentrate on polynomials in three variables, and show the existence of full (strongly) exceptional collection of categories of maximally graded matrix factorizations for invertible weighted homogeneous polynomials. We will also explain how the mirror symmetry naturally explains and generalizes the Arnold's strange duality between the 14 exceptional unimodal singularities.
First we give an overview of the algebraic and the geometric aspects of the mirror symmetry conjecture for weighted homogeneous polynomials. Then we concentrate on polynomials in three variables, and show the existence of full (strongly) exceptional collection of categories of maximally graded matrix factorizations for invertible weighted homogeneous polynomials. We will also explain how the mirror symmetry naturally explains and generalizes the Arnold's strange duality between the 14 exceptional unimodal singularities.
Number Theory Seminar
16:30-17:30 Room #117 (Graduate School of Math. Sci. Bldg.)
Hélène Esnault (Universität Duisburg-Essen)
Finite group actions on the affine space (ENGLISH)
Hélène Esnault (Universität Duisburg-Essen)
Finite group actions on the affine space (ENGLISH)
[ Abstract ]
If $G$ is a finite $\\ell$-group acting on an affine space $\\A^n$ over a
finite field $K$ of cardinality prime to $\\ell$, Serre shows that there
exists a rational fixed point. We generalize this to the case where $K$ is a
henselian discretely valued field of characteristic zero with algebraically
closed residue field and with residue characteristic different from $\\ell$.
We also treat the case where the residue field is finite of cardinality $q$
such that $\\ell$ divides $q-1$. To this aim, we study group actions on weak
N\\'eron models.
(Joint work with Johannes Nicaise)
If $G$ is a finite $\\ell$-group acting on an affine space $\\A^n$ over a
finite field $K$ of cardinality prime to $\\ell$, Serre shows that there
exists a rational fixed point. We generalize this to the case where $K$ is a
henselian discretely valued field of characteristic zero with algebraically
closed residue field and with residue characteristic different from $\\ell$.
We also treat the case where the residue field is finite of cardinality $q$
such that $\\ell$ divides $q-1$. To this aim, we study group actions on weak
N\\'eron models.
(Joint work with Johannes Nicaise)
Seminar on Probability and Statistics
15:00-16:10 Room #000 (Graduate School of Math. Sci. Bldg.)
SUZUKI, Taiji (University of Tokyo)
On multiple kernel learning with elasticnet type regularization (JAPANESE)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2010/05.html
SUZUKI, Taiji (University of Tokyo)
On multiple kernel learning with elasticnet type regularization (JAPANESE)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2010/05.html
2010/10/04
Seminar on Geometric Complex Analysis
10:30-12:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Hideyuki ISHI (Nagoya Univ)
The canonical coordinates associated to homogeneous Kaehler metrics on a homogeneous bounded domain (JAPANESE)
Hideyuki ISHI (Nagoya Univ)
The canonical coordinates associated to homogeneous Kaehler metrics on a homogeneous bounded domain (JAPANESE)
[ Abstract ]
For a real analytic Kaehler manifold, one can define a canonical coordinate, called the Bochner coordinate, around each point. In this talk, we show that the canonical cooredinate is globally defined for a bounded homogeneous domain with a homogeneous Kaehler manifold, which is not necessarily the Bergman metric.
Then we obtain a standard realization of the homogeneous domain associated to the homogeneous metric.
For a real analytic Kaehler manifold, one can define a canonical coordinate, called the Bochner coordinate, around each point. In this talk, we show that the canonical cooredinate is globally defined for a bounded homogeneous domain with a homogeneous Kaehler manifold, which is not necessarily the Bergman metric.
Then we obtain a standard realization of the homogeneous domain associated to the homogeneous metric.
2010/09/28
Tuesday Seminar of Analysis
16:30-18:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Pavel Exner (Czech Academy of Sciences)
Some spectral and resonance properties of quantum graphs (ENGLISH)
Pavel Exner (Czech Academy of Sciences)
Some spectral and resonance properties of quantum graphs (ENGLISH)
[ Abstract ]
In this talk I will discuss three new results about Schr¨odinger operators
on metric graphs obtained in collaboration with Jiri Lipovskyand Brian Davies.
The first one is related to invalidity of the uniform continuation principle for such
operators. One manifestation of this fact are embedded eigenvalues due to
rational relations of graph edge lengths. This effect is non-generic and we show
how geometric perturbations turn these embedded eigenvalues into resonances.
Then second problem is related to high-energy behavior of resonances: we extend
a recent result of Davies and Pushnitski to graphs with general vertex couplings
and find conditions under which the asymptotics does not have Weyl character.
Finally, the last question addressed here concerns the absolutely continuous spectrum
of radial-tree graphs. In a similar vein, we generalize a recent result by Breuer and
Frank that in case of the free (or Kirhhoff) coupling the ac spectrum is absent
provided the edge length are increasing without a bound along the tree.
We show that the result remains valid for a large class of vertex couplings,
but on the other hand, there are nontrivial couplings leading to an ac spectrum.
In this talk I will discuss three new results about Schr¨odinger operators
on metric graphs obtained in collaboration with Jiri Lipovskyand Brian Davies.
The first one is related to invalidity of the uniform continuation principle for such
operators. One manifestation of this fact are embedded eigenvalues due to
rational relations of graph edge lengths. This effect is non-generic and we show
how geometric perturbations turn these embedded eigenvalues into resonances.
Then second problem is related to high-energy behavior of resonances: we extend
a recent result of Davies and Pushnitski to graphs with general vertex couplings
and find conditions under which the asymptotics does not have Weyl character.
Finally, the last question addressed here concerns the absolutely continuous spectrum
of radial-tree graphs. In a similar vein, we generalize a recent result by Breuer and
Frank that in case of the free (or Kirhhoff) coupling the ac spectrum is absent
provided the edge length are increasing without a bound along the tree.
We show that the result remains valid for a large class of vertex couplings,
but on the other hand, there are nontrivial couplings leading to an ac spectrum.
2010/09/14
Infinite Analysis Seminar Tokyo
10:30-14:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Shintarou Yanagida (Kobe Univ.) 10:30-11:30
AGT conjectures and recursion formulas (JAPANESE)
Yuji Yamada (Rikkyo Univ.) 13:00-14:00
classification of solutions to the reflection equation associated to
trigonometrical $R$-matrix of Belavin (JAPANESE)
Shintarou Yanagida (Kobe Univ.) 10:30-11:30
AGT conjectures and recursion formulas (JAPANESE)
Yuji Yamada (Rikkyo Univ.) 13:00-14:00
classification of solutions to the reflection equation associated to
trigonometrical $R$-matrix of Belavin (JAPANESE)
2010/09/13
Infinite Analysis Seminar Tokyo
10:30-15:30 Room #117 (Graduate School of Math. Sci. Bldg.)
Masahiro Kasatani (Tokyo Univ.) 10:30-11:30
Polynomial representations of DAHA of type $C^¥vee C$ and boundary qKZ equations (JAPANESE)
CFT, Isomonodromy deformations and Nekrasov functions (JAPANESE)
Twisted de Rham theory---resonances and the non-resonance (JAPANESE)
Masahiro Kasatani (Tokyo Univ.) 10:30-11:30
Polynomial representations of DAHA of type $C^¥vee C$ and boundary qKZ equations (JAPANESE)
[ Abstract ]
First I will review basic facts about
the double affine Hecke algebra of type $C^¥vee C$
and its polynomial representation.
Next I will intrduce a boundary qKZ equation
and construct its solution in terms of the polynomial representation.
Yasuhiko Yamada (Kobe Univ.) 13:00-14:00First I will review basic facts about
the double affine Hecke algebra of type $C^¥vee C$
and its polynomial representation.
Next I will intrduce a boundary qKZ equation
and construct its solution in terms of the polynomial representation.
CFT, Isomonodromy deformations and Nekrasov functions (JAPANESE)
[ Abstract ]
This talk is an introduction to the relation between conformal filed
theories
and super symmetric gauge theories (Alday-Gaiotto-Tachikawa conjecture)
from the point of view of differential equations (in particular
isomonodromy
deformations).
Katsuhisa Mimachi (Tokyo Institute of Technology) 14:30-15:30This talk is an introduction to the relation between conformal filed
theories
and super symmetric gauge theories (Alday-Gaiotto-Tachikawa conjecture)
from the point of view of differential equations (in particular
isomonodromy
deformations).
Twisted de Rham theory---resonances and the non-resonance (JAPANESE)
2010/09/12
Infinite Analysis Seminar Tokyo
10:30-17:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Hideaki Morita (Muroran Institute of Technology) 10:30-11:30
A factorization formula for Macdonald polynomials at roots of unity (JAPANESE)
W algebras and symmetric polynomials (JAPANESE)
Quantizing the difference Painlev¥'e VI equation (JAPANESE)
On a bijective proof of a factorization formula for Macdonald
polynomials at roots of unity (JAPANESE)
Hideaki Morita (Muroran Institute of Technology) 10:30-11:30
A factorization formula for Macdonald polynomials at roots of unity (JAPANESE)
[ Abstract ]
We consider a combinatorial property of Macdonald polynomials at roots
of unity.
If we made some plethystic substitution to the variables,
Macdonald polynomials are subjected to a certain decomposition rule
when a parameter is specialized at roots of unity.
We review the result and give an outline of the proof.
This talk is based on a joint work with F. Descouens.
Junichi Shiraishi (Tokyo Univ.) 13:00-14:00We consider a combinatorial property of Macdonald polynomials at roots
of unity.
If we made some plethystic substitution to the variables,
Macdonald polynomials are subjected to a certain decomposition rule
when a parameter is specialized at roots of unity.
We review the result and give an outline of the proof.
This talk is based on a joint work with F. Descouens.
W algebras and symmetric polynomials (JAPANESE)
[ Abstract ]
It is well known that we have the factorization property of the Macdonald polynomials under the principal specialization $x=(1,t,t^2,t^3,¥cdots)$. We try to better understand this situation in terms of the Ding-Iohara algebra or the deformend $W$-algebra. Some conjectures are presented in the case of $N$-fold tensor representation of the Fock modules.
Koji Hasegawa (Tohoku Univ.) 14:30-15:30It is well known that we have the factorization property of the Macdonald polynomials under the principal specialization $x=(1,t,t^2,t^3,¥cdots)$. We try to better understand this situation in terms of the Ding-Iohara algebra or the deformend $W$-algebra. Some conjectures are presented in the case of $N$-fold tensor representation of the Fock modules.
Quantizing the difference Painlev¥'e VI equation (JAPANESE)
[ Abstract ]
I will review two constructions for quantum (=non-commutative) version of
q-difference Painleve VI equation.
Yasuhide Numata (Graduate School of Information Science and Technology, Tokyo Univ.) 16:00-17:00I will review two constructions for quantum (=non-commutative) version of
q-difference Painleve VI equation.
On a bijective proof of a factorization formula for Macdonald
polynomials at roots of unity (JAPANESE)
[ Abstract ]
The subject of this talk is a factorization formula for the special
values of modied Macdonald polynomials at roots of unity.
We give a combinatorial proof of the formula, via a result by
Haglund--Haiman--Leohr, for some special classes of partitions,
including two column partitions.
(This talk is based on a joint work with F. Descouens and H. Morita.)
The subject of this talk is a factorization formula for the special
values of modied Macdonald polynomials at roots of unity.
We give a combinatorial proof of the formula, via a result by
Haglund--Haiman--Leohr, for some special classes of partitions,
including two column partitions.
(This talk is based on a joint work with F. Descouens and H. Morita.)
2010/09/11
Infinite Analysis Seminar Tokyo
13:00-17:00 Room #117 (Graduate School of Math. Sci. Bldg.)
Masahiko Ito (School of Science and Technology for Future Life, Tokyo Denki University) 13:00-14:00
Three-term recurrence relations for a $BC_n$-type basic hypergeometric function and their application (JAPANESE)
TBA (JAPANESE)
Masato Taki (YITP Kyoto Univ.) 16:00-17:00
AGT conjecture and geometric engineering (JAPANESE)
Masahiko Ito (School of Science and Technology for Future Life, Tokyo Denki University) 13:00-14:00
Three-term recurrence relations for a $BC_n$-type basic hypergeometric function and their application (JAPANESE)
[ Abstract ]
$BC_n$-type basic hypergeometric series are a certain $q$-analogue
of an integral representation for the Gauss hypergeometric function.
They are defined as multiple $q$-series satisfying Weyl group symmetry of type $C_n$,
and they are a multi-sum generalization of the basic hypergeometric series
in a class of what is called (very-)well-poised. In my talk I will explain
an explicit expression for the $q$-difference system of rank $n+1$
satisfied by a $BC_n$-type basic hypergeometric series with 6+1 parameters
as first order simultaneous $q$-difference equations with a concrete basis.
For this purpose I introduce two types of symmetric Laurent polynomials
which I call the $BC$-type interpolation polynomials. The polynomials satisfy
three-term relations like a contiguous relation for the Gauss hypergeometric
function. As an application, I will show another proof for the product formula
of the $q$-integral introduced by Gustafson.
Masatoshi Noumi (Kobe Univ.) 14:30-15:30$BC_n$-type basic hypergeometric series are a certain $q$-analogue
of an integral representation for the Gauss hypergeometric function.
They are defined as multiple $q$-series satisfying Weyl group symmetry of type $C_n$,
and they are a multi-sum generalization of the basic hypergeometric series
in a class of what is called (very-)well-poised. In my talk I will explain
an explicit expression for the $q$-difference system of rank $n+1$
satisfied by a $BC_n$-type basic hypergeometric series with 6+1 parameters
as first order simultaneous $q$-difference equations with a concrete basis.
For this purpose I introduce two types of symmetric Laurent polynomials
which I call the $BC$-type interpolation polynomials. The polynomials satisfy
three-term relations like a contiguous relation for the Gauss hypergeometric
function. As an application, I will show another proof for the product formula
of the $q$-integral introduced by Gustafson.
TBA (JAPANESE)
Masato Taki (YITP Kyoto Univ.) 16:00-17:00
AGT conjecture and geometric engineering (JAPANESE)
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