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Seminar information archive
Seminar information archive ～04/18｜Today's seminar 04/19 | Future seminars 04/20～
2013/05/10
Lectures
16:30-18:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Laurent Lafforgue (IHES)
Kernels of Langlands' automorphic transfer and non-linear Poisson formulas (ENGLISH)
Laurent Lafforgue (IHES)
Kernels of Langlands' automorphic transfer and non-linear Poisson formulas (ENGLISH)
2013/05/09
Geometry Colloquium
10:00-11:30 Room #122 (Graduate School of Math. Sci. Bldg.)
KIDA Yoshikata (Kyoto University)
Rigidity for amalgamated free products and their envelopes (JAPANESE)
KIDA Yoshikata (Kyoto University)
Rigidity for amalgamated free products and their envelopes (JAPANESE)
[ Abstract ]
For a discrete countable group L, we mean by an envelope of L a locally compact second countable group having a lattice isomorphic to L. In general, it is quite hard to describe all envelopes of a given L. This problem is closely related to orbit equivalence between probability-measure-preserving actions of groups, and also related to Mostow type rigidity. I explain a fundamental idea to attack this problem, and give examples of groups for which the problem is solved. The examples contain mapping class groups of surfaces and certain amalgamated free products. An outline to get an answer for the latter groups will be discussed.
For a discrete countable group L, we mean by an envelope of L a locally compact second countable group having a lattice isomorphic to L. In general, it is quite hard to describe all envelopes of a given L. This problem is closely related to orbit equivalence between probability-measure-preserving actions of groups, and also related to Mostow type rigidity. I explain a fundamental idea to attack this problem, and give examples of groups for which the problem is solved. The examples contain mapping class groups of surfaces and certain amalgamated free products. An outline to get an answer for the latter groups will be discussed.
2013/05/08
Operator Algebra Seminars
16:30-18:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Paul Muhly (University of Iowa)
Boundaries for Tensor Algebras (ENGLISH)
Paul Muhly (University of Iowa)
Boundaries for Tensor Algebras (ENGLISH)
2013/05/07
Tuesday Seminar on Topology
16:30-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Tetsuya Ito (RIMS, Kyoto University)
Homological intersection in braid group representation and dual
Garside structure (JAPANESE)
Tetsuya Ito (RIMS, Kyoto University)
Homological intersection in braid group representation and dual
Garside structure (JAPANESE)
[ Abstract ]
One method to construct linear representations of braid groups is to use
an action of braid groups on certain homology of local system coefficient.
Many famous representations, such as Burau or Lawrence-Krammer-Bigelow
representations are constructed in such a way. We show that homological
intersections on such homology groups are closely related to the dual
Garside structure, a remarkable combinatorial structure of braid, and
prove that some representations detects the length of braids in a
surprisingly simple way.
This work is partially joint with Bert Wiest (Univ. Rennes1).
One method to construct linear representations of braid groups is to use
an action of braid groups on certain homology of local system coefficient.
Many famous representations, such as Burau or Lawrence-Krammer-Bigelow
representations are constructed in such a way. We show that homological
intersections on such homology groups are closely related to the dual
Garside structure, a remarkable combinatorial structure of braid, and
prove that some representations detects the length of braids in a
surprisingly simple way.
This work is partially joint with Bert Wiest (Univ. Rennes1).
Numerical Analysis Seminar
16:30-18:00 Room #123 (Graduate School of Math. Sci. Bldg.)
Takuya Tsuchiya (Ehime University)
Open problems on finite element analysis (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/
Takuya Tsuchiya (Ehime University)
Open problems on finite element analysis (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/
2013/04/30
Lie Groups and Representation Theory
16:30-18:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Hisayosi MATUMOTO (Graduate School of Mathematical Sciences, the University of Tokyo)
The homomorphisms between scalar generalized Verma modules of gl(n,C) with regular infinitesimal characters (JAPANESE)
Hisayosi MATUMOTO (Graduate School of Mathematical Sciences, the University of Tokyo)
The homomorphisms between scalar generalized Verma modules of gl(n,C) with regular infinitesimal characters (JAPANESE)
[ Abstract ]
We will explain the classification of the homomorphisms between scalar generalized Verma modules of gl(n,C) with regular infinitesimal characters. In fact, they are compositions of elementary homomorphisms. The main ingredient of our proof is the translation principle in the mediocre region.
We will explain the classification of the homomorphisms between scalar generalized Verma modules of gl(n,C) with regular infinitesimal characters. In fact, they are compositions of elementary homomorphisms. The main ingredient of our proof is the translation principle in the mediocre region.
Tuesday Seminar on Topology
16:30-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Francis Sergeraert (L'Institut Fourier, Univ. de Grenoble)
Discrete vector fields and fundamental algebraic topology.
(ENGLISH)
Francis Sergeraert (L'Institut Fourier, Univ. de Grenoble)
Discrete vector fields and fundamental algebraic topology.
(ENGLISH)
[ Abstract ]
Robin Forman invented the notion of Discrete Vector Field in 1997.
A recent common work with Ana Romero allowed us to discover the notion
of Eilenberg-Zilber discrete vector field. Giving the topologist a
totally new understanding of the fundamental tools of combinatorial
algebraic topology: Eilenberg-Zilber theorem, twisted Eilenberg-Zilber
theorem, Serre and Eilenberg-Moore spectral sequences,
Eilenberg-MacLane correspondence between topological and algebraic
classifying spaces. Gives also new efficient algorithms for Algebraic
Topology, considerably improving our computer program Kenzo, devoted
to Constructive Algebraic Topology. The talk is devoted to an
introduction to discrete vector fields, the very simple definition of
the Eilenberg-Zilber vector field, and how it can be used in various
contexts.
Robin Forman invented the notion of Discrete Vector Field in 1997.
A recent common work with Ana Romero allowed us to discover the notion
of Eilenberg-Zilber discrete vector field. Giving the topologist a
totally new understanding of the fundamental tools of combinatorial
algebraic topology: Eilenberg-Zilber theorem, twisted Eilenberg-Zilber
theorem, Serre and Eilenberg-Moore spectral sequences,
Eilenberg-MacLane correspondence between topological and algebraic
classifying spaces. Gives also new efficient algorithms for Algebraic
Topology, considerably improving our computer program Kenzo, devoted
to Constructive Algebraic Topology. The talk is devoted to an
introduction to discrete vector fields, the very simple definition of
the Eilenberg-Zilber vector field, and how it can be used in various
contexts.
2013/04/24
Number Theory Seminar
17:30-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Naoki Imai (University of Tokyo)
Good reduction of ramified affinoids in the Lubin-Tate perfectoid space (ENGLISH)
Naoki Imai (University of Tokyo)
Good reduction of ramified affinoids in the Lubin-Tate perfectoid space (ENGLISH)
[ Abstract ]
Recently, Weinstein finds some affinoids in the Lubin-Tate perfectoid space and computes their reduction in equal characteristic case. The cohomology of the reduction realizes the local Langlands correspondence for some representations of GL_h, which are unramified in some sense. In this talk, we introduce other affinoids in the Lubin-Tate perfectoid space in equal characteristic case, whose reduction realizes "ramified" representations of conductor exponent h+1. We call them ramified affinoids. We study the cohomology of the reduction and its relation with the local Langlands correspondence. This is a joint work with Takahiro Tsushima.
Recently, Weinstein finds some affinoids in the Lubin-Tate perfectoid space and computes their reduction in equal characteristic case. The cohomology of the reduction realizes the local Langlands correspondence for some representations of GL_h, which are unramified in some sense. In this talk, we introduce other affinoids in the Lubin-Tate perfectoid space in equal characteristic case, whose reduction realizes "ramified" representations of conductor exponent h+1. We call them ramified affinoids. We study the cohomology of the reduction and its relation with the local Langlands correspondence. This is a joint work with Takahiro Tsushima.
Kavli IPMU Komaba Seminar
17:00-18:30 Room #002 (Graduate School of Math. Sci. Bldg.)
Atsushi Kanazawa (University of British Columbia)
Calabi-Yau threefolds of Type K (ENGLISH)
Atsushi Kanazawa (University of British Columbia)
Calabi-Yau threefolds of Type K (ENGLISH)
[ Abstract ]
We will provide a full classification of Calabi-Yau threefolds of Type
K studied by Oguiso and Sakurai. Our study completes the
classification of Calabi-Yau threefolds with infinite fundamental
group. I will then discuss special Lagrangian T3-fibrations of
Calabi-Yau threefolds of type K. This talk is based on a joint work
with Kenji Hashimoto.
We will provide a full classification of Calabi-Yau threefolds of Type
K studied by Oguiso and Sakurai. Our study completes the
classification of Calabi-Yau threefolds with infinite fundamental
group. I will then discuss special Lagrangian T3-fibrations of
Calabi-Yau threefolds of type K. This talk is based on a joint work
with Kenji Hashimoto.
2013/04/23
Numerical Analysis Seminar
16:30-18:00 Room #002 (Graduate School of Math. Sci. Bldg.)
Hirofumi Notsu (Waseda Institute for Advanced Study)
Pressure-stabilized characteristics finite element schemes for flow problems (JAPANESE)
[ Reference URL ]
http://www.infsup.jp
Hirofumi Notsu (Waseda Institute for Advanced Study)
Pressure-stabilized characteristics finite element schemes for flow problems (JAPANESE)
[ Reference URL ]
http://www.infsup.jp
Tuesday Seminar on Topology
16:30-18:00 Room #056 (Graduate School of Math. Sci. Bldg.)
Andrei Pajitnov (Univ. de Nantes)
Twisted Novikov homology and jump loci in formal and hyperformal spaces (ENGLISH)
Andrei Pajitnov (Univ. de Nantes)
Twisted Novikov homology and jump loci in formal and hyperformal spaces (ENGLISH)
[ Abstract ]
Let X be a CW-complex, G its fundamental group, and R a repesentation of G.
Any element of the first cohomology group of X gives rise to an exponential
deformation of R, which can be considered as a curve in the space of
representations. We show that the cohomology of X with local coefficients
corresponding to the generic point of this curve is computable from a spectral
sequence starting from the cohomology of X with R-twisted coefficients. We
compute the differentials of the spectral sequence in terms of Massey products,
and discuss some particular cases arising in Kaehler geometry when the spectral
sequence degenerates. We explain the relation of these invariants and the
twisted Novikov homology. This is a joint work with Toshitake Kohno.
Let X be a CW-complex, G its fundamental group, and R a repesentation of G.
Any element of the first cohomology group of X gives rise to an exponential
deformation of R, which can be considered as a curve in the space of
representations. We show that the cohomology of X with local coefficients
corresponding to the generic point of this curve is computable from a spectral
sequence starting from the cohomology of X with R-twisted coefficients. We
compute the differentials of the spectral sequence in terms of Massey products,
and discuss some particular cases arising in Kaehler geometry when the spectral
sequence degenerates. We explain the relation of these invariants and the
twisted Novikov homology. This is a joint work with Toshitake Kohno.
2013/04/22
Lectures
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Stefano Olla (Univ. Paris-Dauphine)
Thermal conductivity and weak coupling (ENGLISH)
Stefano Olla (Univ. Paris-Dauphine)
Thermal conductivity and weak coupling (ENGLISH)
[ Abstract ]
We investigate the macroscopic thermal conductivity of a chain of anharmonic oscillators and more general systems, under weak coupling limits and energy conserving stochastic perturbations of the dynamics. In particular we establish a series expansion in the coupling parameter.
We investigate the macroscopic thermal conductivity of a chain of anharmonic oscillators and more general systems, under weak coupling limits and energy conserving stochastic perturbations of the dynamics. In particular we establish a series expansion in the coupling parameter.
Algebraic Geometry Seminar
16:30-18:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Professor Igor Reider (Universite d'Angers / RIMS)
Kodaira-Spencer classes, geometry of surfaces of general type and Torelli
theorem (ENGLISH)
Professor Igor Reider (Universite d'Angers / RIMS)
Kodaira-Spencer classes, geometry of surfaces of general type and Torelli
theorem (ENGLISH)
[ Abstract ]
In this talk I will explain a geometric interpretation of Kodaira-Spencer classes and apply
it to the study of the differential of the period map of weight 2 Hodge structures for surfaces
of general type.
My approach is based on interpreting Kodaira-Spencer classes as higher rank bundles and
then studing their stability. This naturally leads to two parts:
1) unstable case
2) stable case.
I will give a geometric characterization of the first case and show how to relate the second
case to a special family of vector bundles giving rise to a family of rational curves. This family
of rational curves is used to recover the surface in question.
In this talk I will explain a geometric interpretation of Kodaira-Spencer classes and apply
it to the study of the differential of the period map of weight 2 Hodge structures for surfaces
of general type.
My approach is based on interpreting Kodaira-Spencer classes as higher rank bundles and
then studing their stability. This naturally leads to two parts:
1) unstable case
2) stable case.
I will give a geometric characterization of the first case and show how to relate the second
case to a special family of vector bundles giving rise to a family of rational curves. This family
of rational curves is used to recover the surface in question.
Seminar on Geometric Complex Analysis
10:30-12:00 Room #126 (Graduate School of Math. Sci. Bldg.)
Yusaku Tiba (Tokyo Institute of Technology)
Kobayashi hyperbolic imbeddings into low degree surfaces in three dimensional projective spaces (JAPANESE)
Yusaku Tiba (Tokyo Institute of Technology)
Kobayashi hyperbolic imbeddings into low degree surfaces in three dimensional projective spaces (JAPANESE)
[ Abstract ]
We construct smooth irreducible curves of the lowest possible degree in quadric and cubic surfaces whose complements are Kobayashi hyperbolically imbedded into those surfaces. This is a joint work with Atsushi Ito.
We construct smooth irreducible curves of the lowest possible degree in quadric and cubic surfaces whose complements are Kobayashi hyperbolically imbedded into those surfaces. This is a joint work with Atsushi Ito.
2013/04/20
Harmonic Analysis Komaba Seminar
13:00-18:00 Room #128 (Graduate School of Math. Sci. Bldg.)
Hiroki Saito (Tokyo Metropolitan University) 13:30-15:00
Directional maximal operators and radial weights on the plane
(JAPANESE)
Boundedness of Trace operator for Besov spaces with variable
exponents
(JAPANESE)
Hiroki Saito (Tokyo Metropolitan University) 13:30-15:00
Directional maximal operators and radial weights on the plane
(JAPANESE)
[ Abstract ]
Let $\\Omega$ be a set of unit vectors and $w$ be a radial weight on the plane. We consider the weighted directional maximal operator defined by
$M_{\\Omega,w}f(x):=\\sup_{x\\in R\\in \\cB_{\\Omega}}\\frac{1}{w(R)}\\int_{R}|f(y)|w(y)dy$,
where $\\cB_{\\Omega}$ denotes the all rectangles on the plane whose longest side is parallel to some unit vector in $\\Omega$ and $w(R)$ denotes $\\int_{R}w$.
In this talk we give a sufficient condition of the weight
for an almost-orthogonality principle related to these maximal operators to hold. The condition allows us to get weighted norm inequality
$\\|M_{\\Omega,w}f\\|_{L^2(w)}\\le C \\log N \\|f\\|_{L^2(w)}$,
when $w(x)=|x|^a$, $a>0$, and $\\Omega$ is a set of unit vectors on the plane with cardinality $N\\gg 1$.
Takahiro Noi (Chuo University) 15:30-17:00Let $\\Omega$ be a set of unit vectors and $w$ be a radial weight on the plane. We consider the weighted directional maximal operator defined by
$M_{\\Omega,w}f(x):=\\sup_{x\\in R\\in \\cB_{\\Omega}}\\frac{1}{w(R)}\\int_{R}|f(y)|w(y)dy$,
where $\\cB_{\\Omega}$ denotes the all rectangles on the plane whose longest side is parallel to some unit vector in $\\Omega$ and $w(R)$ denotes $\\int_{R}w$.
In this talk we give a sufficient condition of the weight
for an almost-orthogonality principle related to these maximal operators to hold. The condition allows us to get weighted norm inequality
$\\|M_{\\Omega,w}f\\|_{L^2(w)}\\le C \\log N \\|f\\|_{L^2(w)}$,
when $w(x)=|x|^a$, $a>0$, and $\\Omega$ is a set of unit vectors on the plane with cardinality $N\\gg 1$.
Boundedness of Trace operator for Besov spaces with variable
exponents
(JAPANESE)
2013/04/19
PDE Real Analysis Seminar
10:30-11:30 Room #056 (Graduate School of Math. Sci. Bldg.)
Katsuyuki Ishii (Kobe University)
An approximation scheme for the anisotropic and the planar crystalline curvature flow (JAPANESE)
Katsuyuki Ishii (Kobe University)
An approximation scheme for the anisotropic and the planar crystalline curvature flow (JAPANESE)
[ Abstract ]
In 2004 Chambolle proposed an algorithm for the mean curvature flow based on a variational problem. Since then, some extensions of his algorithm have been studied.
In this talk we would like to discuss the convergence of the anisotropic variant of his algorithm by use of the anisotropic signed distance function. An application to the approximation for the planar motion by crystalline curvature is also discussed.
In 2004 Chambolle proposed an algorithm for the mean curvature flow based on a variational problem. Since then, some extensions of his algorithm have been studied.
In this talk we would like to discuss the convergence of the anisotropic variant of his algorithm by use of the anisotropic signed distance function. An application to the approximation for the planar motion by crystalline curvature is also discussed.
2013/04/18
Geometry Colloquium
10:00-11:30 Room #122 (Graduate School of Math. Sci. Bldg.)
Yasuyuki Nagatomo (Meiji University)
Harmonic maps into Grassmannian manifolds (JAPANESE)
Yasuyuki Nagatomo (Meiji University)
Harmonic maps into Grassmannian manifolds (JAPANESE)
[ Abstract ]
A harmonic map from a Riemannian manifold into a Grassmannian manifold is characterized by a vector bundle, a space of sections of the bundle and the Laplace operator. This characterization can be considered as a generalization of Theorem of Takahashi on minimal immersions into a sphere (J.Math.Soc.Japan 18 (1966)) and implies the well-known fact that the Kodaira embedding is a harmonic map.
We apply the main result to generalize a Theorem of do Carmo and Wallach (Ann.of Math. 93 (1971)) and describe a moduli space of harmonic maps with constant energy densities and some properties about pull-back bundles and connections from a Riemannian homogeneous space into a Grassmannian. We give some applications including a rigidity of minimal immersions from the complex projective line to complex projective spaces (S.Bando and Y.Ohnita, J. Math. Soc. Japan 39 (1987)).
The ADHM-construction of instantons gives a family of maps into Grassmannians via monad theory on the twistor space. These maps are, in general, not harmonic maps, but are similar to maps obtained in our generalized do Carmo-Wallach theorem. We compare these two constructions of moduli spaces.
A harmonic map from a Riemannian manifold into a Grassmannian manifold is characterized by a vector bundle, a space of sections of the bundle and the Laplace operator. This characterization can be considered as a generalization of Theorem of Takahashi on minimal immersions into a sphere (J.Math.Soc.Japan 18 (1966)) and implies the well-known fact that the Kodaira embedding is a harmonic map.
We apply the main result to generalize a Theorem of do Carmo and Wallach (Ann.of Math. 93 (1971)) and describe a moduli space of harmonic maps with constant energy densities and some properties about pull-back bundles and connections from a Riemannian homogeneous space into a Grassmannian. We give some applications including a rigidity of minimal immersions from the complex projective line to complex projective spaces (S.Bando and Y.Ohnita, J. Math. Soc. Japan 39 (1987)).
The ADHM-construction of instantons gives a family of maps into Grassmannians via monad theory on the twistor space. These maps are, in general, not harmonic maps, but are similar to maps obtained in our generalized do Carmo-Wallach theorem. We compare these two constructions of moduli spaces.
2013/04/17
Operator Algebra Seminars
16:30-18:00 Room #118 (Graduate School of Math. Sci. Bldg.)
Tamar Friedmann (Univ. Rochester)
Singularities, algebras, and the string landscape (ENGLISH)
Tamar Friedmann (Univ. Rochester)
Singularities, algebras, and the string landscape (ENGLISH)
2013/04/16
Lie Groups and Representation Theory
16:30-18:30 Room #126 (Graduate School of Math. Sci. Bldg.)
Michael Pevzner (Reims University) 16:30-17:30
Non-standard models for small representations of GL(n,R) (ENGLISH)
Degenerate principal series of symplectic groups (ENGLISH)
Michael Pevzner (Reims University) 16:30-17:30
Non-standard models for small representations of GL(n,R) (ENGLISH)
[ Abstract ]
We shall present new models for some parabolically induced
unitary representations of the real general linear group which involve Weyl symbolic calculus and furnish very efficient tools in studying branching laws for such representations.
Pierre Clare (Penn. State University, USA) 17:30-18:30We shall present new models for some parabolically induced
unitary representations of the real general linear group which involve Weyl symbolic calculus and furnish very efficient tools in studying branching laws for such representations.
Degenerate principal series of symplectic groups (ENGLISH)
[ Abstract ]
We will discuss properties of representations of symplectic groups induced from maximal parabolic subgroups of Heisenberg type, including K-types formulas, expressions of intertwining operators and the study of their spectrum.
We will discuss properties of representations of symplectic groups induced from maximal parabolic subgroups of Heisenberg type, including K-types formulas, expressions of intertwining operators and the study of their spectrum.
2013/04/15
Lectures
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)
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.
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.
Lectures
16:45-18:15 Room #126 (Graduate School of Math. Sci. Bldg.)
Amir Dembo (Stanford University)
Persistence Probabilities (ENGLISH)
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.
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)
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.
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.
2013/04/11
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)
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.
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.
2013/04/10
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)
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)
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.
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.
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