Seminar information archive

Seminar information archive ~05/25Today's seminar 05/26 | Future seminars 05/27~



15:00-16:30   Room #126 (Graduate School of Math. Sci. Bldg.)
Janna Lierl (University of Bonn)
Two-sided bounds for the Dirichlet heat kernel on inner uniform domains (ENGLISH)
[ Abstract ]
I will present sharp two-sided bounds for the heat kernel in domains with Dirichlet boundary conditions. The domain is assumed to satisfy an inner uniformity condition. This includes any convex domain, the complement of any convex domain in Euclidean space, and the interior of the Koch snowflake.
The heat kernel estimates hold in the abstract setting of metric measure spaces equipped with a (possibly non-symmetric) Dirichlet form. The underlying space is assumed to satisfy a Poincare inequality and volume doubling.
The results apply, for example, to the Dirichlet heat kernel associated with a divergence form operator with bounded measurable coefficients and symmetric, uniformly elliptic second order part.
This is joint work with Laurent Saloff-Coste.


16:45-18:15   Room #126 (Graduate School of Math. Sci. Bldg.)
Amir Dembo (Stanford University)
Persistence Probabilities (ENGLISH)
[ Abstract ]
Persistence probabilities concern how likely it is that a stochastic process has a long excursion above fixed level and of what are the relevant scenarios for this behavior. Power law decay is expected in many cases of physical significance and the issue is to determine its power exponent parameter. I will survey recent progress in this direction (jointly with Jian Ding, Fuchang Gao, and Sumit Mukherjee), dealing with random algebraic polynomials of independent coefficients, iterated partial sums and other auto-regressive sequences, and with the solution to heat equation initiated by white noise.

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Nikolay Shcherbina (University of Wuppertal)
On defining functions for unbounded pseudoconvex domains (ENGLISH)
[ Abstract ]
We show that every strictly pseudoconvex domain $\Omega$ with smooth boundary in a complex manifold $M$ admits a global defining function, i.e. a smooth plurisubharmonic function $\varphi \colon U \to \mathbf{R}$ defined on an open neighbourhood $U \subset M$ of $\Omega$ such that $\Omega =\{ \varphi < 0 \}$, $d\varphi \not= 0$ on $b\Omega$ and $\varphi$ is strictly plurisubharmonic near $b\Omega$. We then introduce the notion of the kernel $K(\Omega)$ of an arbitrary domain $\Omega \subset M$ as the set of all points where every smooth and bounded from above plurisubharmonic function on $\Omega$ fails to be strictly plurisubharmonic. If $\Omega$ is not relatively compact in $M$, then in general $K(\Omega)$ is nonempty, even in the case when $M$ is Stein. It is shown that every strictly pseudoconvex domain $\Omega \subset M$ with smooth boundary admits a global defining function that is strictly plurisubharmonic precisely in the complement of $K(\Omega)$. We then investigate properties of the kernel. Among other results we prove 1-pseudoconcavity of the kernel, we show that in general the kernel does not possess any analytic structure, and we investigate Liouville type properties of the kernel.


Geometry Colloquium

10:00-11:30   Room #122 (Graduate School of Math. Sci. Bldg.)
Jeff Viaclovsky (University of Wisconsin)
Critical metrics on connected sums of Einstein four-manifolds (ENGLISH)
[ Abstract ]
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.


Operator Algebra Seminars

16:30-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Takuya Takeishi (Univ. Tokyo)
On nuclearity of $C^*$-algebras associated with Fell bundles over \\'etale groupoids (ENGLISH)

Number Theory Seminar

17:30-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Deepam Patel (University of Amsterdam)
Motivic structure on higher homotopy of non-nilpotent spaces (ENGLISH)
[ Abstract ]
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.


Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Hiroyuki Fuji (The University of Tokyo)
Colored HOMFLY Homology and Super-A-polynomial (JAPANESE)
[ Abstract ]
This talk is based on works in collaboration with S. Gukov, M. Stosic,
and P. Sulkowski. We study the colored HOMFLY homology for knots and
its asymptotic behavior. In recent years, the categorification of the
colored HOMFLY polynomial is proposed in term of homological
discussions via spectral sequence and physical discussions via refined
topological string, and these proposals give the same answer
miraculously. In this talk, we consider the asymptotic behavior of the
colored HOMFLY homology \\`a la the generalized volume conjecture, and
discuss the quantum structure of the colored HOMFLY homology for the
complete symmetric representations via the generalized A-polynomial
which we call “super-A-polynomial”.

Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Atsumu Sasaki (Tokai University)
A characterization of non-tube type Hermitian symmetric spaces by visible actions
[ Abstract ]
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.


Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Akito Futaki (University of Tokyo)
K\\"ahler-Einstein metrics and K stability (JAPANESE)
[ Abstract ]
I will describe an outline of the proof of the equivalence between the existence of K\\"ahler-Einstein metrics and K-stablity after Chen-Donaldson-Sun and Tian.


Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Yoshiki Oshima (Kavli IPMU, the University of Tokyo)
Discrete branching laws of Zuckerman's derived functor modules (JAPANESE)
[ Abstract ]
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.


Infinite Analysis Seminar Tokyo

13:30-15:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Simon Wood (Kavli IPMU)
On the extended algebra of type sl_2 at positive rational level (ENGLISH)
[ Abstract ]
I will be presenting my recent work with Akihiro Tsuchiya
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.


Tuesday Seminar on Topology

16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Keiko Kawamuro (University of Iowa)
Open book foliation and application to contact topology (ENGLISH)
[ Abstract ]
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).


Operator Algebra Seminars

16:00-17:30   Room #118 (Graduate School of Math. Sci. Bldg.)
Hiroshi Ando (IHES)
Ultraproducts of von Neumann algebras (JAPANESE)


15:00-17:30   Room #050 (Graduate School of Math. Sci. Bldg.)
NOGUCHI, Junjiro (University of Tokyo) 15:00-16:00
Value distribution theory and analytic function theory in several variables (JAPANESE)
OSHIMA, Toshio (University of Tokyo) 16:30-17:30
My fifty years of differential equations (JAPANESE)


Operator Algebra Seminars

15:45-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Lucio Cirio (Univ. M\"unster) 15:45-16:45
Infinitesimal 2-Yang-Baxter operators from a categorification
of the Knizhnik-Zamolodchikov connection (ENGLISH)
Sutanu Roy (Univ. G\"ottingen) 17:00-18:00
Twisted tensor product of $C^*$-algebras (ENGLISH)

Numerical Analysis Seminar

10:00-12:15   Room #056 (Graduate School of Math. Sci. Bldg.)
Irene Vignon-Clementel (INRIA Paris Rocquencourt )
Complex flow at the boundaries of branched models: numerical aspects (ENGLISH)
[ Reference URL ]

Operator Algebra Seminars

14:30-15:30   Room #118 (Graduate School of Math. Sci. Bldg.)
Stefano Rossi (Univ. Roma II)
The connected component of a compact quantum group (ENGLISH)

Operator Algebra Seminars

13:15-14:15   Room #118 (Graduate School of Math. Sci. Bldg.)
Jean Roydor (Univ. Bordeaux)
Two Amir-Cambern type theorems for $C^*$-algebras (ENGLISH)

PDE Real Analysis Seminar

10:30-11:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Caterina Zeppieri (Universität Münster)
Geometric rigidity for incompatible fields and an application to strain-gradient plasticity (ENGLISH)
[ Abstract ]
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).


Operator Algebra Seminars

09:45-12:00   Room #123 (Graduate School of Math. Sci. Bldg.)
Tristan Bice (York Univ.) 09:45-10:45
Traces and Ultrapowers (ENGLISH)
David Penneys (Univ. Toronto) 11:00-12:00
Constructing subfactors with jellyfish (ENGLISH)

Operator Algebra Seminars

13:30-18:15   Room #123 (Graduate School of Math. Sci. Bldg.)
Danny Hey (Univ. Toronto) 13:30-14:30
Classification and the Toms-Winter Conjecture (ENGLISH)
Stephen Curran (UCLA) 14:45-15:45
Free probability and planar algebras (ENGLISH)
Rasmus Bentmann (Univ. Copenhagen) 16:00-17:00
Kirchberg $X$-algebras with real rank zero and intermediate cancellation (ENGLISH)
Luis Santiago-Moreno (Univ. Oregon) 17:15-18:15
Classifying $C^*$-algebras up to W-stability (ENGLISH)

GCOE Seminars

14:45-15:45   Room #123 (Graduate School of Math. Sci. Bldg.)
Stephen Curran (UCLA)
Free probability and planar algebras (ENGLISH)
[ Reference URL ]


FMSP Lectures

10:30-12:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Benjamin Burton (The University of Queensland, Australia)
Knots, algorithms and linear programming: the quest to solve unknot recognition in polynomial time (ENGLISH)
[ Abstract ]
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.


Seminar on Probability and Statistics

14:50-16:00   Room #006 (Graduate School of Math. Sci. Bldg.)
MAESONO, Yoshihiko (Kyushu University)
Smoothing of sign test and approximation of its p-value (JAPANESE)
[ Abstract ]
In this talk we discuss theoretical properties of smoothed sign test, which based on a kernel estimator of the underlying distribution function of data. We show the smoothed sign test is equivalent to the usual sign test in the sense of Pitman efficiency, and its main term of the variance does not depend on the distribution of the population, under the null hypothesis. Though smoothed sign test is not distribution-free, we can obtain Edgeworth expansion which does not depend on the distribution. This is a joint work with Ms. Mengxin Lu of Kyushu University.
[ Reference URL ]



16:00-17:30   Room #117 (Graduate School of Math. Sci. Bldg.)
Frederic Le Roux (Institut de Mathematiques de Jussieu, Universite Pierre et Marie Curie)
The rotation set around a fixed point for surface homeomorphisms. (ENGLISH)
[ Abstract ]
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.

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