## Tuesday Seminar on Topology

Date, time & place Tuesday 17:00 - 18:30 056Room #056 (Graduate School of Math. Sci. Bldg.) KOHNO Toshitake, KAWAZUMI Nariya, KITAYAMA Takahiro, SAKASAI Takuya Tea: 16:30 - 17:00 Common Room

Seminar information archive

### 2013/03/19

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).

### 2013/02/19

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Eri Hatakenaka (Tokyo University of Agriculture and Technology)
On the ring of Fricke characters of free groups (JAPANESE)
[ Abstract ]
This is a joint work with Takao Satoh (Tokyo University of Science). We study a descending filtration of the ring of Fricke characters of a free group consisting of ideals on which the automorphism group of the free group naturally acts. Then by using it, we define a descending filtration of the automorphism group of a free group, and investigate a relation between it and the Andreadakis-Johnson filtration.

### 2013/01/22

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Jarek Kedra (University of Aberdeen)
On the autonomous metric of the area preserving diffeomorphism
of the two dimensional disc. (ENGLISH)
[ Abstract ]
Let D be the open unit disc in the Euclidean plane and let
G:=Diff(D, area) be the group of smooth compactly supported
area-preserving diffeomorphisms of D. A diffeomorphism is called
autonomous if it is the time one map of the flow of a time independent
vector field. Every diffeomorphism in G is a composition of a number
of autonomous diffeomorphisms. The least amount of such
diffeomorphisms defines a norm on G. In the talk I will investigate
geometric properties of such a norm.

In particular I will construct a bi-Lipschitz embedding of the free
abelian group of arbitrary rank to G. I will also show that the space
of homogeneous quasi-morphisms vanishing on all autonomous
diffeomorphisms in G is infinite dimensional.

This is a joint work with Michael Brandenbursky.

### 2013/01/21

16:30-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Naoki Kato (The University of Tokyo
)
Lie foliations transversely modeled on nilpotent Lie
algebras
(JAPANESE)
[ Abstract ]
To each Lie $\\mathfrak{g}$-foliation, there is an associated subalgebra
$\\mathfrak{h}$ of $\\mathfrak{g}$ with the foliation, which is called the
structure Lie algabra. In this talk, we will explain the inverse problem,
that is, which pair $(\\mathfrak{g},\\mathfrak{h})$ can be realized as a
Lie $\\mathfrak{g}$-foliation with the structure Lie algabra $\\mathfrak{h}$, under the assumption that $\\mathfrak{g}$ is nilpotent.

### 2013/01/21

17:30-18:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Tomohiko Ishida (The University of Tokyo)
Quasi-morphisms on the group of area-preserving diffeomorphisms of
the 2-disk
(JAPANESE)
[ Abstract ]
Gambaudo and Ghys constructed linearly independent countably many quasi-
morphisms on the group of area-preserving diffeomorphisms of the 2-disk
from quasi-morphisms on braid groups.
In this talk, we will explain that their construction is injective as a
homomorphism between vector spaces of quasi-morphisms.
If time permits, we introduce an application by Brandenbursky and K\\c{e}
dra.

### 2012/12/11

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Ismar Volic (Wellesley College)
Homotopy-theoretic methods in the study of spaces of knots and links (ENGLISH)
[ Abstract ]
I will survey the ways in which some homotopy-theoretic
methods, manifold calculus of functors main among them, have in recent
years been used for extracting information about the topology of
be featured. I will end with some recent results about spaces of
homotopy string links and in particular about how one can use functor
calculus in combination with configuration space integrals to extract

### 2012/12/04

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Yoshitake Hashimoto (Tokyo City University)
Conformal field theory for C2-cofinite vertex algebras (JAPANESE)
[ Abstract ]
This is a jount work with Akihiro Tsuchiya (Kavli IPMU).
We consider sheaves of covacua and conformal blocks over parameter spaces of n-pointed Riemann surfaces
for a vertex algebra of which the category of modules is not necessarily semi-simple.
We assume the C2-cofiniteness condition for vertex algebras.
We define "tensor product" of two modules over a C2-cofinite vertex algebra.

### 2012/11/27

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Hiraku Nozawa (JSPS-IHES fellow)
On a finite aspect of characteristic classes of foliations (JAPANESE)
[ Abstract ]
Characteristic classes of foliations are not bounded due to Thurston.
In this talk, we will explain finiteness of characteristic classes for
foliations with certain transverse structures (e.g. transverse
conformally flat structure) and its relation to unboundedness and
rigidity of foliations.
(This talk is based on a joint work with Jesús Antonio
Álvarez López at University of Santiago de Compostela,
which is available as arXiv:1205.3375.)

### 2012/11/20

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Kentaro Nagao (Nagoya University)
3 dimensional hyperbolic geometry and cluster algebras (JAPANESE)
[ Abstract ]
The cluster algebra was discovered by Fomin-Zelevinsky in 2000.
Recently, the structures of cluster algebras are recovered in
many areas including the theory of quantum groups, low
dimensional topology, discrete integrable systems, Donaldson-Thomas
theory, and string theory and there is dynamic development in the
research on these subjects. In this talk I introduce a relation between
3 dimensional hyperbolic geometry and cluster algebras motivated
by some duality in string theory.

### 2012/11/13

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Takahiro Kitayama (RIMS, Kyoto University,JSPS PD)
The virtual fibering theorem and sutured manifold hierarchies (JAPANESE)
[ Abstract ]
In 2007 Agol showed that every irreducible 3-manifold whose fundamental
group is nontrivial and virtually residually finite rationally solvable
(RFRS) is virtually fibered. In the proof he used the theory of
least-weight taut normal surfaces introduced and developed by Oertel and
Tollefson-Wang. We give another proof using complexities of sutured
manifolds. This is a joint work with Stefan Friedl (University of
Cologne).

### 2012/11/06

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Furusho Hidekazu (Nagoya University)
Galois action on knots (JAPANESE)
[ Abstract ]
I will explain a motivic structure on knots.
Then I will explain that the absolute Galois group of
the rational number field acts non-trivially
on 'the space of knots' in a non-trivial way.

### 2012/10/30

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Koya Shimokawa (Saitama University)
Applications of knot theory to molecular biology (JAPANESE)
[ Abstract ]
In this talk we discuss applications of knot theory to studies of DNA
and proteins.
Especially we will consider (1)topological characterization of
mechanisms of site-specific recombination systems,
(2)modeling knotted DNA and proteins in confined regions using lattice
knots, and
(3)mechanism of topoisomerases and signed crossing changes.

### 2012/10/23

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Nariya Kawazumi (The University of Tokyo)
A geometric approach to the Johnson homomorphisms (JAPANESE)
[ Abstract ]
We re-construct the Johnson homomorphisms as an embeddig of the Torelli
group
into the completed Goldman-Turaev Lie bialgebra. Then the image is
included in the
kernel of the Turaev cobracket. In the case where the boundary is
connected,
the Turaev cobracket clarifies a geometric meaning of the Morita traces.
Time permitting, we also discuss the case of holed discs.
This talk is based on a joint work with Yusuke Kuno (Tsuda College).

### 2012/10/16

17:10-18:10   Room #056 (Graduate School of Math. Sci. Bldg.)
Ken-Ichi Yoshikawa (Kyoto University)
Analytic torsion of log-Enriques surfaces (JAPANESE)
[ Abstract ]
Log-Enriques surfaces are rational surfaces with nowhere vanishing
pluri-canonical forms. We report the recent progress on the computation
of analytic torsion of log-Enriques surfaces.

### 2012/10/09

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Michihiko Fujii (Kyoto University)
The growth series of pure Artin groups of dihedral type (JAPANESE)
[ Abstract ]
In this talk, I consider the kernel of the natural projection from
the Artin group of dihedral type to the corresponding Coxeter group,
that we call a pure Artin group of dihedral type,
and present rational function expressions for both the spherical and
geodesic growth series
of the pure Artin group of dihedral type with respect to a natural
generating set.
Also, I show that their growth rates are Pisot numbers.
This talk is partially based on a joint work with Takao Satoh.

### 2012/10/02

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Akito Futaki (The University of Tokyo)
Geometric flows and their self-similar solutions
(JAPANESE)
[ Abstract ]
In the first half of this expository talk we consider the Ricci flow and its self-similar solutions,
namely the Ricci solitons. We then specialize in the K\\"ahler case and discuss on the K\\"ahler-Einstein
problem. In the second half of this talk we consider the mean curvature flow and its self-similar
solutions, and see common aspects of the two geometric flows.

### 2012/09/04

17:00-18:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Piotr Nowak (the Institute of Mathematics, Polish Academy of Sciences)
Poincare inequalities, rigid groups and applications (ENGLISH)
[ Abstract ]
Kazhdan’s property (T) for a group G can be expressed as a
fixed point property for affine isometric actions of G on a Hilbert
space. This definition generalizes naturally to other normed spaces. In
this talk we will focus on the spectral (aka geometric) method for
proving property (T), based on the work of Garland and studied earlier
by Pansu, Zuk, Ballmann-Swiatkowski, Dymara-Januszkiewicz
(“lambda_1>1/2” conditions) and we generalize it to to the setting of
all reflexive Banach spaces.
As applications we will show estimates of the conformal dimension of the
boundary of random hyperbolic groups in the Gromov density model and
present progress on Shalom’s conjecture on vanishing of 1-cohomology
with coefficients in uniformly bounded representations on Hilbert spaces.

### 2012/07/24

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Greg McShane (Institut Fourier, Grenoble)
Orthospectra and identities (ENGLISH)
[ Abstract ]
The orthospectra of a hyperbolic manifold with geodesic
boundary consists of the lengths of all geodesics perpendicular to the
boundary.
We discuss the properties of the orthospectra, asymptotics, multiplicity
and identities due to Basmajian, Bridgeman and Calegari. We will give
a proof that the identities of Bridgeman and Calegari are the same.

### 2012/07/17

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Mutsuo Oka (Tokyo University of Science)
Contact structure of mixed links (JAPANESE)
[ Abstract ]
A strongly non-degenerate mixed function has a Milnor open book
structures on a sufficiently small sphere. We introduce the notion of
{\\em a holomorphic-like} mixed function
and we will show that a link defined by such a mixed function has a
canonical contact structure.
Then we will show that this contact structure for a certain
holomorphic-like mixed function
is carried by the Milnor open book.

### 2012/07/10

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Marcus Werner (Kavli IPMU)
Topology in Gravitational Lensing (ENGLISH)
[ Abstract ]
General relativity implies that light is deflected by masses
due to the curvature of spacetime. The ensuing gravitational
lensing effect is an important tool in modern astronomy, and
topology plays a significant role in its properties. In this
talk, I will review topological aspects of gravitational lensing
theory: the connection of image numbers with Morse theory; the
interpretation of certain invariant sums of the signed image
magnification in terms of Lefschetz fixed point theory; and,
finally, a new partially topological perspective on gravitational
light deflection that emerges from the concept of optical geometry
and applications of the Gauss-Bonnet theorem.

### 2012/06/19

17:10-18:10   Room #056 (Graduate School of Math. Sci. Bldg.)
Yukio Matsumoto (Gakushuin University)
On the universal degenerating family of Riemann surfaces
over the D-M compactification of moduli space (JAPANESE)
[ Abstract ]
It is usually understood that over the Deligne-
Mumford compactification of moduli space of Riemann surfaces of
genus > 1, there is a family of stable curves. However, if one tries to
construct this family precisely, he/she must first take a disjoint union
of various types of smooth families of stable curves, and then divide
them by their automorphisms to paste them together. In this talk we will
show that once the smooth families are divided, the resulting quotient
family contains not only stable curves but virtually all types of
degeneration of Riemann surfaces, becoming a kind of universal
degenerating family of Riemann surfaces.

### 2012/06/12

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Takefumi Nosaka (RIMS, Kyoto University, JSPS)
Topological interpretation of the quandle cocycle invariants of links (JAPANESE)
[ Abstract ]
Carter et al. introduced many quandle cocycle invariants
combinatorially constructed from link-diagrams. For connected quandles of
finite order, we give a topological meaning of the invariants, without
some torsion parts. Precisely, this invariant equals a sum of "knot
colouring polynomial" and of a Z-equivariant part of the Dijkgraaf-Witten
invariant. Moreover, our approach involves applications to compute "good"
torsion subgroups of the 3-rd quandle homologies and the 2-nd homotopy
groups of rack spaces.

### 2012/06/05

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Yusuke Kuno (Tsuda College)
A generalization of Dehn twists (JAPANESE)
[ Abstract ]
We introduce a generalization
of Dehn twists for loops which are not
necessarily simple loops on an oriented surface.
Our generalization is an element of a certain
enlargement of the mapping class group of the surface.
A natural question is whether a generalized Dehn twist is
in the mapping class group. We show some results related to this question.
This talk is partially based on a joint work
with Nariya Kawazumi (Univ. Tokyo).

### 2012/05/29

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Inasa Nakamura (Gakushuin University, JSPS)
Triple linking numbers and triple point numbers
of torus-covering $T^2$-links
(JAPANESE)
[ Abstract ]
The triple linking number of an oriented surface link was defined as an
torus-covering $T^2$-link $\\mathcal{S}_m(a,b)$ is a surface link in the
form of an unbranched covering over the standard torus, determined from
two commutative $m$-braids $a$ and $b$.
In this talk, we consider $\\mathcal{S}_m(a,b)$ when $a$, $b$ are pure
$m$-braids ($m \\geq 3$), which is a surface link with $m$-components. We
present the triple linking number of $\\mathcal{S}_m(a,b)$ by using the
linking numbers of the closures of $a$ and $b$. This gives a lower bound
of the triple point number. In some cases, we can determine the triple
point numbers, each of which is a multiple of four.

### 2012/05/22

17:10-18:10   Room #056 (Graduate School of Math. Sci. Bldg.)
Hiroshi Iritani (Kyoto University)
Gamma Integral Structure in Gromov-Witten theory (JAPANESE)
[ Abstract ]
The quantum cohomology of a symplectic
manifold undelies a certain integral local system
defined by the Gamma characteristic class.
This local system originates from the natural integral
local sysmem on the B-side under mirror symmetry.
In this talk, I will explain its relationships to the problem
of analytic continuation of Gromov-Witten theoy (potentials),
including crepant resolution conjecture, LG/CY correspondence,
modularity in higher genus theory.