Seminar information archive

Seminar information archive ~08/18Today's seminar 08/19 | Future seminars 08/20~

2014/06/19

Geometry Colloquium

10:00-11:30   Room #122 (Graduate School of Math. Sci. Bldg.)
Takashi Sakai (Tokyo Metropolitan University)
Antipodal structure of the intersection of real forms and its applications (JAPANESE)
[ Abstract ]
A subset A of a Riemannian symmetric space is called an antipodal set if the geodesic symmetry s_x fixes all points of A for each x in A. This notion was first introduced by Chen and Nagano. Tanaka and Tasaki proved that the intersection of two real forms L_1 and L_2 in a Hermitian symmetric space of compact type is an antipodal set of L_1 and L_2. As an application, we calculate the Lagrangian Floer homology of a pair of real forms in a monotone Hermitian symmetric space. Then we obtain a generalization of the Arnold-Givental inequality. We expect to generalize the above results to the case of complex flag manifolds. In fact, using the k-symmetric structure, we can describe an antipodal set of a complex flag manifold. Moreover we can observe the antipodal structure of the intersection of certain real forms in a complex flag manifold.

This talk is based on a joint work with Hiroshi Iriyeh and Hiroyuki Tasaki.

2014/06/18

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Yuki Arano (Univ. Tokyo)
Toward the classification of irreducible unitary spherical representations of the Drinfeld double of $SU_q(3)$ (ENGLISH)

2014/06/17

Tuesday Seminar on Topology

16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Yoshifumi Matsuda (Aoyama Gakuin University)
Bounded Euler number of actions of 2-orbifold groups on the circle (JAPANESE)
[ Abstract ]
Burger, Iozzi and Wienhard defined the bounded Euler number for a
continuous action of the fundamental group of a connected oriented
surface of finite type possibly with punctures on the circle. A Milnor-Wood
type inequality involving the bounded Euler number holds and its maximality
characterizes Fuchsian actions up to semiconjugacy. The definition of the
bounded Euler number can be extended to actions of 2-orbifold groups by
considering coverings. A Milnor-Wood type inequality and the characterization
of Fuchsian actions also hold in this case. In this talk, we describe when lifts
of Fuchsian actions of certain 2-orbifold groups, such as the modular group,
are characterized by its bounded Euler number.

Number Theory Seminar

17:30-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Bao Châu Ngô (University of Chicago, VIASM)
Vinberg's monoid and automorphic L-functions (ENGLISH)
[ Abstract ]
We will explain a generalisation of the construction of the local factors of Godement-Jacquet's L-functions, based on Vinberg's monoid.

Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Pablo Ramacher (Marburg University)
SINGULAR EQUIVARIANT ASYMPTOTICS AND THE MOMENTUM MAP. RESIDUE FORMULAE IN EQUIVARIANT COHOMOLOGY (ENGLISH)
[ Abstract ]
Let M be a smooth manifold and G a compact connected Lie group acting on M by isometries. In this talk, we study the equivariant cohomology of the cotangent bundle of M, and relate it to the cohomology of the Marsden-Weinstein reduced space via certain residue formulae. In case of compact symplectic manifolds with a Hamiltonian G-action, similar residue formulae were derived by Jeffrey, Kirwan et al..

2014/06/16

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Hideyuki Ishi (Nagoya University)
New examples of weighted Bergman kernels on a certain non-homogeneous Siegel domain (JAPANESE)

Kavli IPMU Komaba Seminar

16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
A.P. Veselov (Loughborough, UK and Tokyo)
Universal formulae for Lie groups and Chern-Simons theory (ENGLISH)
[ Abstract ]
In 1990s Vogel introduced an interesting parametrization of simple
Lie algebras by 3 parameters defined up to a common multiple and
permutations. Numerical characteristic is called universal if it can be
expressed in terms of Vogel's parameters (example - the dimension of Lie
algebra). I will discuss some universal formulae for Lie groups
and Chern-Simons theory on 3D sphere.
The talk is based on joint work with R.L. Mkrtchyan and A.N. Sergeev.

2014/06/11

Operator Algebra Seminars

16:30-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Yosuke Kubota (Univ. Tokyo)
Finiteness of K-area and the dual of the Baum-Connes conjecture (ENGLISH)

Mathematical Biology Seminar

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Tetsuya Kobayashi (Center for Research on Integrated Biomedical Systems, Institute of Industrial Science, the University of Tokyo
)
Path Integral Formulation and Variational Structure in Multitype Population Dynamics
(JAPANESE)

2014/06/10

Lectures

14:40-16:10   Room #056 (Graduate School of Math. Sci. Bldg.)
Sergei Duzhin (Steklov Institute of Mathematics)
Bipartite knots (ENGLISH)
[ Abstract ]
We give a solution to a part of Problem 1.60 in Kirby's list of open
problems in topology thus proving a conjecture raised in 1987 by
J.Przytycki. A knot is said to be bipartite if it has a "matched" diagram,
that is, a plane diagram that has an even number of crossings which can be
split into pairs that look like a simple braid on two strands with two
crossings. The conjecture was that there exist knots that do not have such
diagrams. I will prove this fact using higher Alexander ideals.
This talk is based on a joint work with my student M.Shkolnikov

Seminar on Mathematics for various disciplines

10:30-11:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Yoshifumi Kimura (Graduate School of Mathematics, Nagoya University)
The self-similar collapse solution of a point vortex system and complex time singularities (JAPANESE)
[ Abstract ]
A system of N point vortices is a Hamiltonian dynamical system with N degrees of freedom,and it is known that under certain parameter and initial conditions, there are self-similar collapse solutions for which N vortices collide at a point while rotating without changing the initial shape of configuration. In this talk, I will introduce such collision solutions and discuss some properties of complex time singularities in relation with those solutions.

Tuesday Seminar of Analysis

16:30-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Ken Abe (Nagoya University)
On estimates for the Stokes flow in a space of bounded functions (JAPANESE)
[ Abstract ]
The Stokes equations are well understood on $L^p$ space for various kinds of domains such as bounded or exterior domains, and fundamental to study the nonlinear Navier-Stokes equations. The situation is different for the case $p=\\infty$ since in this case the Helmholtz projection does not act as a bounded operator anymore. In this talk, we show some a priori estimate for a composition operator of the Stokes semigroup and the Helmholtz projection on a space of bounded functions. 

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Yuka Kotorii (The University of Tokyo)
On relation between the Milnor's $¥mu$-invariant and HOMFLYPT
polynomial (JAPANESE)
[ Abstract ]
Milnor introduced a family of invariants for ordered oriented link,
called $¥bar{¥mu}$-invariants. Polyak showed a relation between the $¥
bar{¥mu}$-invariant of length 3 sequence and Conway polynomial.
Moreover, Habegger-Lin showed that Milnor's invariants are invariants of
string link, called $¥mu$-invariants. We show that any $¥mu$-invariant
of length $¥leq k$ can be represented as a combination of HOMFLYPT
polynomials if all $¥mu$-invariant of length $¥leq k-2$ vanish.
This result is an extension of Polyak's result.

2014/06/09

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Ryosuke Takahashi (Nagoya University)
Modified Kähler-Ricci flow on projective bundles (JAPANESE)

Numerical Analysis Seminar

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Issei Oikawa (Waseda University)
A hybridized discontinuous Galerkin method with weak stabilization (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/

2014/06/06

Colloquium

16:30-17:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Mikhail Kapranov (Kavli IPMU)
Lie algebras from secondary polytopes (ENGLISH)
[ Abstract ]
The secondary polytope of a point configuration
in the Euclidean space was introduced by Gelfand, Zelevinsky
and the speaker long time ago in order to understand discriminants
of multi-variable polynomials. These polytopes have
a remarkable factorization (or operadic) property: each
face of any secondary polytope is isomorphic to the
product of several other secondary polytopes.

The talk, based on joint work in progress with M. Kontsevich
and Y. Soibelman, will explain how the factorization property
can be used to construct Lie algebra-type objects:
$L_¥infty$ and $A_¥infty$-algebras. These algebras
turn out to be related to the problem of deformation
of triangulated categories with semiorthogonal decompositions.

2014/06/04

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Ion Nechita (Univ. Paul Sabatier)
Positive and completely positive maps via free additive powers of probability measures (ENGLISH)

2014/06/03

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Tatsuru Takakura (Chuo University)
Vector partition functions and the topology of multiple weight varieties
(JAPANESE)
[ Abstract ]
A multiple weight variety is a symplectic quotient of a direct product
of several coadjoint orbits of a compact Lie group $G$, with respect to
the diagonal action of the maximal torus. Its geometry and topology are
closely related to the combinatorics concerned with the weight space
decomposition of a tensor product of irreducible representations of $G$.
For example, when considering the Riemann-Roch index, we are naturally
lead to the study of vector partition functions with multiplicities.
In this talk, we discuss some formulas for vector partition functions,
especially a generalization of the formula of Brion-Vergne. Then, by
using
them, we investigate the structure of the cohomology of certain multiple
weight varieties of type $A$ in detail.

2014/06/02

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Atsushi Hayashimoto (Nagano National College of Technology)
Generalized pseudoellipsoids and proper holomorphic mappings between them (JAPANESE)

Algebraic Geometry Seminar

15:30-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Yusuke Nakamura (University of Tokyo)
On base point free theorem for log canonical three folds over the algebraic closure of a finite field (JAPANESE)
[ Abstract ]
We will discuss about the base point free theorem on three-dimensional
pairs defined over the algebraic closure of a finite field.

We know the base point free theorem on arbitrary-dimensional Kawamata
log terminal pairs in characteristic zero. By Birkar and Xu, the base
point free theorem in positive characteristic is known for big line
bundles on three-dimensional Kawamata log terminal pairs defined over
an algebraically closed field of characteristic larger than 5. Over the
algebraic closure of a finite field, a stronger result was proved by Keel.

The purpose of this talk is to generalize the Keel's result. We will
prove the base point free theorem for big line bundles on
three-dimensional log canonical pairs defined over the algebraic closure
of a finite field. This theorem is not valid for another field.

This is joint work with Diletta Martinelli and Jakub Witaszek.

2014/05/28

Number Theory Seminar

16:40-17:40   Room #056 (Graduate School of Math. Sci. Bldg.)
Gantsooj Batzaya (University of Tokyo)
On simultaneous approximation to powers of a real number by rational numbers (ENGLISH)

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Makoto Yamashita (Ochanomizu University)
Poisson boundary of monoidal categories (ENGLISH)

Mathematical Biology Seminar

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Keisuke Ejima (Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo
)
Modeling the social contagion: The obesity epidemic and its control (JAPANESE)
[ Abstract ]
:As an obesity epidemic has grown worldwide, a variety of
intervention programs have been considered, but a scientific approach
to comparatively assessing the control programs has still to be
considered. The present study aims to describe an obesity epidemic by
employing a simple mathematical model that accounts for both social
contagion and non-contagious hazards of obesity, thereby comparing the
effectiveness of different types of interventions.
An epidemiological model is devised to describe the time- and
age-dependent risk of obesity, the hazard of which is dealt with as
both dependent on and independent of obesity prevalence, and
parameterizing the model using empirically observed data. The
equilibrium prevalence is investigated as our epidemiological outcome,
assessing its sensitivity to different parameters that regulate the
impact of intervention programs and qualitatively comparing the
effectiveness. We compare the effectiveness of different types of
interventions, including those directed to never-obese individuals
(i.e. primary prevention) and toward obese and ex-obese individuals
(i.e. secondary prevention).
The optimal choice of intervention programs considerably varies with
the transmission coefficient of obesity, and a limited
transmissibility led us to favour preventing weight gain among
never-obese individuals. An abrupt decline in the prevalence is
expected when the hazards of obesity through contagious and
non-contagious routes fall into a particular parameter space, with a
high sensitivity to the transmission potential of obesity from person
to person. When a combination of two control strategies can be
selected, primary and secondary preventions yielded similar population
impacts and the superiority of the effectiveness depends on the
strength of the interventions at an individual level.
The optimality of intervention programs depends on the contagiousness
of obesity. Filling associated data gaps of obesity transmission would
help systematically understand the epidemiological dynamics and
consider required control programs.

2014/05/27

Tuesday Seminar of Analysis

16:30-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Yoichi Miyazaki (NIHON UNIVERSITY, SCHOOL OF DENTISTRY)
The regularity theorem for elliptic equations and the smoothness of domains (JAPANESE)
[ Abstract ]
We consider the Dirichlet boundary problem for a strongly elliptic operator of order $2m$ with non-smooth coefficients, and prove the regularity theorem for $L_p$-based Sobolev spaces when the domain has a boundary of limited smoothness. Compared to the known results, we can weaken the smoothness assumption on the boundary by $m-1$.

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Ege Fujikawa (Chiba University)
The Teichmuller space and the stable quasiconformal mapping class group for a Riemann surface of infinite type (JAPANESE)
[ Abstract ]
We explain recent developments of the theory of infinite dimensional Teichmuller space. In particular, we observe the dynamics of the orbits by the action of the stable quasiconformal mapping class group on the Teichmuller space and consider the relationship with the asymptotic Teichmuller space. We also introduce the generalized fixed point theorem and the Nielsen realization theorem. Furthermore, we investigate the moduli space of Riemann surface of infinite type.

< Previous 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138 Next >