Tuesday Seminar on Topology

Seminar information archive ~04/19Next seminarFuture seminars 04/20~

Date, time & place Tuesday 17:00 - 18:30 056Room #056 (Graduate School of Math. Sci. Bldg.)
Organizer(s) KAWAZUMI Nariya, KITAYAMA Takahiro, SAKASAI Takuya

Seminar information archive


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Masahiko Kanai (The University of Tokyo)
Rigidity of group actions via invariant geometric structures (JAPANESE)
[ Abstract ]
It is a homomorphism into a FINITE dimensional Lie group that is concerned with in the classical RIGIDITY theorems such as those of Mostow and Margulis. In the meantime, differentiable GROUP ACTIONS for which we ask rigidity problems is a homomorphism into a diffeomorphism group, which is a typical example of INFINITE dimensional Lie groups. The purpose of the present talk is exhibiting several rigidity theorems for group actions in which I have been involved for years. Although quite a few fields of mathematics, such as ergodic theory, the theory of smooth dynamical systems, representation theory and so on, have made remarkable contributions to rigidity problems, I would rather emphasis geometric aspects: I would focus on those rigidity phenomenon for group actions that are observed by showing that the actions have INVARIANT GEOMETRIC STRUCTURES.


17:00-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Takehiko Morita (Osaka University)
Measures with maximum total exponent and generic properties of $C^
{1}$ expanding maps (JAPANESE)
[ Abstract ]
This is a joint work with Yusuke Tokunaga. Let $M$ be an $N$
dimensional compact connected smooth Riemannian manifold without
boundary and let $\\mathcal{E}^{r}(M,M)$ be the space of $C^{r}$
expandig maps endowed with $C^{r}$ topology. We show that
each of the following properties for element $T$ in $\\mathcal{E}
^{1}(M,M)$ is generic.
\\item[(1)] $T$ has a unique measure with maximum total exponent.
\\item[(2)] Any measure with maximum total exponent for $T$ has
zero entropy.
\\item[(3)] Any measure with maximum total exponent for $T$ is
fully supported.
On the contrary, we show that for $r\\ge 2$, a generic element
in $\\mathcal{E}^{r}(M,M)$ has no fully supported measures with
maximum total exponent.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Masahiko Yoshinaga (Kyoto University)
Minimal Stratifications for Line Arrangements (JAPANESE)
[ Abstract ]
The homotopy type of complements of complex
hyperplane arrangements have a special property,
so called minimality (Dimca-Papadima and Randell,
around 2000). Since then several approaches based
on (continuous, discrete) Morse theory have appeared.
In this talk, we introduce the "dual" object, which we
call minimal stratification for real two dimensional cases.
A merit is that the minimal stratification can be explicitly
described in terms of semi-algebraic sets.
We also see associated presentation of the fundamental group.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Atsushi Ishii (University of Tsukuba)
Quandle colorings with non-commutative flows (JAPANESE)
[ Abstract ]
This is a joint work with Masahide Iwakiri, Yeonhee Jang and Kanako Oshiro.
We introduce quandle coloring invariants and quandle cocycle invariants
with non-commutative flows for knots, spatial graphs, handlebody-knots,
where a handlebody-knot is a handlebody embedded in the $3$-sphere.
Two handlebody-knots are equivalent if one can be transformed into the
other by an isotopy of $S^3$.
The quandle coloring (resp. cocycle) invariant is a ``twisted'' quandle
coloring (resp. cocycle) invariant.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Tetsuya Ito (The University of Tokyo)
Isotated points in the space of group left orderings (JAPANESE)
[ Abstract ]
The set of all left orderings of a group G admits a natural
topology. In general the space of left orderings is homeomorphic to the
union of Cantor set and finitely many isolated points. In this talk I
will give a new method to construct left orderings corresponding to
isolated points, and will explain how such isolated orderings reflect
the structures of groups.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Taro Yoshino (The University of Tokyo)
Topological Blow-up (JAPANESE)
[ Abstract ]
Suppose that a Lie group $G$ acts on a manifold
$M$. The quotient space $X:=G\\backslash M$ is locally compact,
but not Hausdorff in general. Our aim is to understand
such a non-Hausdorff space $X$.
The space $X$ has the crack $S$. Roughly speaking, $S$ is
the causal subset of non-Hausdorffness of $X$, and especially
$X\\setminus S$ is Hausdorff.

We introduce the concept of `topological blow-up' as a `repair'
of the crack. The `repaired' space $\\tilde{X}$ is
locally compact and Hausdorff space containing $X\\setminus S$
as its open subset. Moreover, the original space $X$ can be
recovered from the pair of $(\\tilde{X}, S)$.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Susumu Hirose (Tokyo University of Science)
On diffeomorphisms over non-orientable surfaces embedded in the 4-sphere (JAPANESE)
[ Abstract ]
For a closed orientable surface standardly embedded in the 4-sphere,
it was known that a diffeomorphism over this surface is extendable to
the 4-sphere if and only if this diffeomorphism preserves
the Rokhlin quadratic form of this surafce.
In this talk, we will explain an approach to the same kind of problem for
closed non-orientable surfaces.


16:30-17:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Chikara Haruta (Graduate School of Mathematical Sciences, the University of Tokyo )
On unknotting of surface-knots with small sheet numbers
[ Abstract ]
A connected surface smoothly embedded in ${\\mathbb R}^4$ is called a surface-knot. In particular, if a surface-knot $F$ is homeomorphic to the $2$-sphere or the torus, then it is called an $S^2$-knot or a $T^2$-knot, respectively. The sheet number of a surface-knot is an invariant analogous to the crossing number of a $1$-knot. M. Saito and S. Satoh proved some results concerning the sheet number of an $S^2$-knot. In particular, it is known that an $S^2$-knot is trivial if and only if its sheet number is $1$, and there is no $S^2$-knot whose sheet number is $2$. In this talk, we show that there is no $S^2$-knot whose sheet number is $3$, and a $T^2$-knot is trivial if and only if its sheet number is $1$.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Nariya Kawazumi (The University of Tokyo)
The Chas-Sullivan conjecture for a surface of infinite genus (JAPANESE)
[ Abstract ]
Let \\Sigma_{\\infty,1} be the inductive limit of compact
oriented surfaces with one boundary component. We prove the
center of the Goldman Lie algebra of the surface \\Sigma_{\\infty,1}
is spanned by the constant loop.
A similar statement for a closed oriented surface was conjectured
by Chas and Sullivan, and proved by Etingof. Our result is deduced
from a computation of the center of the Lie algebra of oriented chord
If time permits, the Lie bracket on the space of linear chord diagrams
will be discussed. This talk is based on a joint work with Yusuke Kuno
(Hiroshima U./JSPS).


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Kenneth Schackleton (IPMU)
On the coarse geometry of Teichmueller space (ENGLISH)
[ Abstract ]
We discuss the synthetic geometry of the pants graph in
comparison with the Weil-Petersson metric, whose geometry the
pants graph coarsely models following work of Brock’s. We also
restrict our attention to the 5-holed sphere, studying the Gromov
bordification of the pants graph and the dynamics of pseudo-Anosov
mapping classes.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Raphael Ponge (The University of Tokyo)
Diffeomorphism-invariant geometries and noncommutative geometry (ENGLISH)
[ Abstract ]
In many geometric situations we may encounter the action of
a group $G$ on a manifold $M$, e.g., in the context of foliations. If
the action is free and proper, then the quotient $M/G$ is a smooth
manifold. However, in general the quotient $M/G$ need not even be
Hausdorff. Furthermore, it is well-known that a manifold has structure
invariant under the full group of diffeomorphisms except the
differentiable structure itself. Under these conditions how can one do
diffeomorphism-invariant geometry?

Noncommutative geometry provides us with the solution of trading the
ill-behaved space $M/G$ for a non-commutative algebra which
essentially plays the role of the algebra of smooth functions on that
space. The local index formula of Atiyah-Singer ultimately holds in
the setting of noncommutative geometry. Using this framework Connes
and Moscovici then obtained in the 90s a striking reformulation of the
local index formula in diffeomorphism-invariant geometry.

An important part the talk will be devoted to reviewing noncommutative
geometry and Connes-Moscovici's index formula. We will then hint to on-
going projects about reformulating the local index formula in two new
geometric settings: biholomorphism-invariant geometry of strictly
pseudo-convex domains and contactomorphism-invariant geometry.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Nobuhiro Nakamura (The University of Tokyo)
Pin^-(2)-monopole equations and intersection forms with local coefficients of 4-manifolds (JAPANESE)
[ Abstract ]
We introduce a variant of the Seiberg-Witten equations, Pin^-(2)-monopole equations, and explain its applications to intersection forms with local coefficients of 4-manifolds.
The first application is an analogue of Froyshov's results on 4-manifolds which have definite forms with local coefficients.
The second one is a local coefficient version of Furuta's 10/8-inequality.
As a corollary, we construct nonsmoothable spin 4-manifolds satisfying Rohlin's theorem and the 10/8-inequality.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Noboru Ito (Waseda University)
On a colored Khovanov bicomplex (JAPANESE)
[ Abstract ]
We discuss the existence of a bicomplex which is a Khovanov-type
complex associated with categorification of a colored Jones polynomial.
This is an answer to the question proposed by A. Beliakova and S. Wehrli.
Then the second term of the spectral sequence of the bicomplex corresponds
to the Khovanov-type homology group. In this talk, we explain how to define
the bicomplex. If time permits, we also define a colored Rasmussen invariant
by using another spectral sequence of the colored Jones polynomial.


17:00-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Ken'ichi Ohshika (Osaka University)
Characterising bumping points on deformation spaces of Kleinian groups (JAPANESE)
[ Abstract ]
It is known that components of the interior of a deformation space of a Kleinian group can bump, and a component of the interior can bump itself, on the boundary of the deformation space.
Anderson-Canary-McCullogh gave a necessary and sufficient condition for two components to bump.
In this talk, I shall give a criterion for points on the boundary to be bumping points.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Daniel Ruberman (Brandeis University)
Periodic-end manifolds and SW theory (ENGLISH)
[ Abstract ]
We study an extension of Seiberg-Witten invariants to
4-manifolds with the homology of S^1 \\times S^3. This extension has
many potential applications in low-dimensional topology, including the
study of the homology cobordism group. Because b_2^+ =0, the usual
strategy for defining invariants does not work--one cannot disregard
reducible solutions. In fact, the count of solutions can jump in a
family of metrics or perturbations. To remedy this, we define an
index-theoretic counter-term that jumps by the same amount. The
counterterm is the index of the Dirac operator on a manifold with a
periodic end modeled at infinity by the infinite cyclic cover of the
manifold. This is joint work with Tomasz Mrowka and Nikolai Saveliev.


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)
[ 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 $A$.


16:30-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
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.


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)
[ 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.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Ayumu Inoue (Tokyo Institute of Technology)
Quandle homology and complex volume
(Joint work with Yuichi Kabaya) (JAPANESE)
[ Abstract ]
For a hyperbolic 3-manifold M, the complex value (Vol(M) + i CS(M)) is called the complex volume of M. Here, Vol(M) denotes the volume of M, and CS(M) the Chern-Simons invariant of M.
In 2004, Neumann defined the extended Bloch group, and showed that there is an element of the extended Bloch group corresponding to a hyperbolic 3-manifold.
He further showed that we can compute the complex volume of the manifold by evaluating the element of the extended Bloch group.
To obtain an element of the extended Bloch group corresponding to a hyperbolic 3-manifold, we have to find an ideal triangulation of the manifold and to solve several equations.
On the other hand, we show that the element of the extended Bloch group corresponding to the exterior of a hyperbolic link is obtained from a quandle shadow coloring.
It means that we can compute the complex volume combinatorially from a link diagram.


17:00-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Keiko Kawamuro (University of Iowa)
A polynomial invariant of pseudo-Anosov maps (JAPANESE)
[ Abstract ]
Thurston-Nielsen classified surface homomorphism into three classes. Among them, the pseudo-Anosov class is the most interesting since there is strong connection to the hyperbolic manifolds. As an invariant, the dilatation number has been known. In this talk, I will introduce a new invariant of pseudo-Anosov maps. It is an integer coefficient polynomial, which contains the dilatation as the largest real root and is often reducible. I will show properties of the polynomials, examples, and some application to knot theory. (This is a joint work with Joan Birman and Peter Brinkmann.)


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Marion Moore (University of California, Davis)
High Distance Knots in closed 3-manifolds (ENGLISH)
[ Abstract ]
Let M be a closed 3-manifold with a given Heegaard splitting.
We show that after a single stabilization, some core of the
stabilized splitting has arbitrarily high distance with respect
to the splitting surface. This generalizes a result of Minsky,
Moriah, and Schleimer for knots in S^3. We also show that in the
complex of curves, handlebody sets are either coarsely distinct
or identical. We define the coarse mapping class group of a
Heeegaard splitting, and show that if (S,V,W) is a Heegaard
splitting of genus greater than or equal to 2, then the coarse
mapping class group of (S,V,W) is isomorphic to the mapping class
group of (S, V, W). This is joint work with Matt Rathbun.


17:00-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Akira Kono (Kyoto University)
On the cohomology of free and twisted loop spaces (JAPANESE)
[ Abstract ]
A natural extension of cohomology suspension to a free loop space is
constructed from the evaluation map and is shown to have a good
properties in cohomology calculation. This map is generalized to a
twisted loop space.
As an application, the cohomology of free and twisted loop space of
classifying spaces of compact Lie groups, including certain finite
Chevalley groups is calculated.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Takahiro Kitayama (The University of Tokyo)
Non-commutative Reidemeister torsion and Morse-Novikov theory (JAPANESE)
[ Abstract ]
For a circle-valued Morse function of a closed oriented manifold, we
show that Reidemeister torsion over a non-commutative formal Laurent
polynomial ring equals the product of a certain non-commutative
Lefschetz-type zeta function and the algebraic torsion of the Novikov
complex over the ring. This gives a generalization of the results of
Hutchings-Lee and Pazhitnov on abelian coefficients. As a consequence we
obtain Morse theoretical and dynamical descriptions of the higher-order
Alexander polynomials.


16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Kazuhiro Ichihara (Nihon University)
On exceptional surgeries on Montesinos knots
(joint works with In Dae Jong and Shigeru Mizushima) (JAPANESE)
[ Abstract ]
I will report recent progresses of the study on exceptional
surgeries on Montesinos knots.
In particular, we will focus on how homological invariants (e.g.
khovanov homology,
knot Floer homology) on knots can be used in the study of Dehn surgery.


17:00-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Taro Asuke (The University of Tokyo)
On Fatou-Julia decompositions (JAPANESE)
[ Abstract ]
We will explain that Fatou-Julia decompositions can be
introduced in a unified manner to several kinds of one-dimensional
complex dynamical systems, which include the action of Kleinian groups,
iteration of holomorphic mappings and complex codimension-one foliations.
In this talk we will restrict ourselves mostly to the cases where the
dynamical systems have a certain compactness, however, we will mention
how to deal with dynamical systems without compactness.

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