117

Problems on Low‐dimensional Topology, 2019
Edited by T. Ohtsuki1

This is a list of open problems on low‐dimensional topology with expositions of
their history, background, significance, or importance. This list was made by editing
manuscripts written by contributors of open problems to the problem session of theconference “Intelligence of Low‐dimensional Topology” held at Research Institutefor Mathematical Sciences, Kyoto University in May 22‐24, 2019.

Contents

1

Crossing numbers of composite knots and spatial graphs22

Correspondence between local moves and invariants of virtual knots

5

3

Rectilinear spatial complete graphs

64Instanton Floer theory for 3‐manifolds and the homology cobor‐dism group of integral homology 3‐spheres

8

5

The AMU Conjecture for self‐homeomorphisms of surfaces and thevolume conjecture for 3‐manifolds
10

6

The mapping class group of a surface and the quantum invariantsof integral homology 3‐spheres
11

7

Positive flow‐spines and contact 3‐manifolds

13

lResearch Institute for Mathematical Sciences, Kyoto University, Sakyo‐ku, Kyoto, 606‐8502, JAPAN
Email: tomotada@kurims.kyoto‐u.ac.jp
The editor is partially supported by JSPS KAKENHI Grant Numbers JP16H02145 and1

JP16K13754.

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1

Crossing numbers of composite knots and spatial graphs(Benjamin Bode)2This section is a collection of problems that relate to the question of the additivityof the crossing number under the connected sum operation, i. e., for two knots K_{1}and K_{2} is c(K_{1}\# K_{2})=c(K_{1})+c(K_{2}) ? This problem is extremely difficult, but
the related problems I am going to discuss could give some insights on the crossing
number of K_{1}\# K_{2} without us having to tackle the conjecture itself.
Malyutin [23] showed that if c(K_{1}\# K_{2})\geq c(K_{1}) for all knots K_{1}, K_{2} or ifc(K_{1} \# K_{2})\geq\frac{2}{3}(c(K_{1})+c(K_{2})) for all knots K_{1}, K_{2} , then hyperbolic knots are
not generic, meaning that the percentage of hyperbolic knots amongst all of theprime knots of n or fewer crossings approaches 100 as n approaches infinity, a con‐jecture that was widely believed to be true until then. A positive answer to some ofthe questions below would disprove this conjecture.
Let S\subset S^{3} be diffeomorphic to the standard 2‐sphere S^{2} and denote the twoballs that are bounded by S by B_{1} and B_{2} . Let A and B be distinct points on
S . For a fixed projection direction we are interested in the number of crossings ofa simple path from A to B that lies completely in one of the B_{i}s . We say a path\gamma :[0,1]arrow B_{i} with \gamma(0)=A, \gamma(1)=B and \gamma(s)\neq\gamma(t) for all s\neq t\in[0,1] isminimal in B_{i} if c(\gamma)\leq c(\gamma') for all such paths \gamma' . A minimal path \gamma_{i} in B_{i} might

not be unique (not even up to isotopy). Figure la) shows an example of S andminimal paths \gamma_{i} in B_{i} . We can see that one of them, \gamma_{2} , is isotopic to a path in S.

a)b)

Figure 1: a) The path \gamma_{1} is minimal in B_{1} with c(\gamma_{1})=0 . The path \gamma_{2} is minimal in B_{2} withc(\gamma_{2})=3 . The path \gamma_{2} is isotopic to a path in S=\partial B_{2}=\partial B_{1} , while \gamma_{1} is not. b) The path \gamma_{2} isminimal in B_{2} with respect to \alpha_{1} with c(\gamma_{2}\cup\alpha_{1})=6 and is isotopic to a path in S.

Question 1.1 (B. Bode). Given S, A, B and a projection direction, is it always
true that there is an i\in\{1,2\} and a path \gamma_{i} that is minimal in B_{i} and that isisotopic (with fixed endpoints) to a path in S ‘?
2Department of Mathematics, Osaka University, Toyonaka, Osaka 560‐0043, Japanben. bode. 2013@my.bristol.ac.uk

2

119This question becomes more relevant to the additivity of the crossing number if
we change the situation slightly.
In addition to S, A, B and the fixed projection direction we are now also given
two simple paths, \alpha_{i} : [0,1]arrow B_{i} from A to B . We say a simple path \gamma : [0,1]arrow B_{i}from A to B is minimal in B_{i} with respect to \alpha_{j}, j\neq i if c(\gamma\cup\alpha_{j})\leq c(\gamma'\cup\alpha_{j}) forall such paths \gamma' . An example is depicted in Figure lb).

Question 1.2 (B. Bode). Given S, A, B, \alpha_{i} and a projection direction, is it always
true that there is an i\in\{1,2\} and a path \gamma_{i} that is minimal in B_{i} with respect to\alpha_{j}, j\neq i and that is isotopic (with fixed endpoints) to a path in S^{l}?
A positive answer to this question would imply that c(K_{1} \# K_{2})\geq\min\{c(K_{1}), c(K_{2})\}and would therefore show that hyperbolic knots are not generic in the sense of [23].
a)

b)

c)

Figure 2: a) The planar graph \theta^{2}. b ) The spatial graph \theta_{3_{1},4_{1} ^{2}. c ) An element of \Omega_{3_{1},4_{1} ^{2} , which is
not \theta_{3_{1},4_{1} ^{2} . Here the constituent knots are 3_{1}\# 4_{1} and 3_{1} (each twice).

The next question aims at connections between the crossing numbers of composite

knots and spatial graphs as in [4]. Let \theta^{2} be the planar graph with two vertices thatare connected by four edges, shown in Figure 2a ). We label the edges by x_{1}, x_{2},z_{1}and z_{2} in no particular order. Let \theta_{K_{1},K_{2} ^{2} be the spatial graph that results fromtying the x ‐edges into the knot K_{1} and the z ‐edges into K_{2} as in Figure 2b ). The
unions of any pair of distinct edges of this spatial graph form knots, the constituent

knots of the spatial graph, namely either K_{1}\# K_{2} ( x_{i} with z_{j} ), K_{1}\# K_{1} ( x_{i} with x_{j} )or K_{2}\# K_{2} ( z_{i} and z_{j} ). Let \Omega_{K_{1},K_{2} ^{2} be the set of isotopy classes of embeddings of \theta^{2}
such that its constituent knots are as follows:\bullet\bulletx_{i}\cup z_{j}=K_{1}\# K_{2} for all i, j=1,2,x_{i}\cup x_{j}=K_{1}\# K_{1} and z_{i}\cup z_{j}=K_{2}\# K_{2} or both are prime. (In particular, they
are not unknots.)

From this definition it is clear that\theta_{K_{1},K_{2} ^{2}\in\Omega_{K_{1},K_{2} ^{2}.

Question 1.3 (B. Bode). Is c(\theta_{K_{1},K_{2}})\leq c(\Gamma) for all \Gamma\in\Omega_{K_{1},K_{2}^{\beta)} ^{2}.
3

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It follows from [4] that a positive answer to this question would imply thatc(K_{1} \# K_{2})\geq\frac{1}{4}(c(K_{1}\# K_{1})+c(K_{2}\# K_{2}) .

(1)

Note that we do not know c(\theta_{K_{1},K_{2} ^{2}) , since we do not know if the diagram in Figure2b) is minimal.
a)

b)

c)

Figure 3: a) For this choice of P and Q the black arc \gamma minimizes c(D') because it does not add
any crossings to D . The constituent knots of this theta curve are 3_{1}\# 4_{1},3_{1} and 4_{1} . b) For adifferent choice of P and Q the black curve has to intersect D somewhere. The shown arc does so
the minimal number of times possible. The constituent knots of this theta curve are 3_{1}\# 4_{1},3_{1} and
4_{1}. c) Changing the signs of crossings between the black arc and the diagram D does not change
the fact that \gamma minimzes c(D') for this choice of endpoints P and Q . It can change the constituent
knots however. Here they are 3_{1}\# 4_{1},3_{1} and the unknot.

Let

D be a knot diagram of a composite knot

K_{1}\# K_{2} . Pick an arbitrary point
For any additional point Q on D any simple path \gamma from P to Q that does
not intersect K_{1}\# K_{2} turns the knot diagram into a diagram D'=D\cup\gamma of a spatial
graph (a theta‐curve \theta ), one of whose constituent knots is K_{1}\# K_{2}.
Let \gamma' be a path that minimizes c(D') among all simple paths from P to Q that
do not intersect K_{1}\# K_{2} . Again this minimizer is usually not unique. An example
for two different choices of P and Q , where D is the minimal diagram of 3_{1}\# 4_{1} isgiven in Figure 3.
P on D .

Question 1.4 (B. Bode). Given any diagram D of K_{1}\# K_{2} , does there exist a choiceof P and Q such that there is a simple path \gamma' from P to Q that does not intersect
K_{1}\# K_{2} , that minimizes c(D') and such that the constituent knots of \theta are K_{1}\# K_{2},K_{1} and K_{2} ?

A positive answer to this question would imply that c(K_{1} \# K_{2})>\frac{2}{3}(c(K_{1})+c(K_{2}))and therefore also show that the conjecture on the genericity of hyperbolic knots isfalse [23].

4

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121

2

Correspondence between local moves and invariants ofvirtual knots(Shin Satoh3)
The set of welded knots is a quotient of the set of virtual knots, by the move“overcrossings commute” It is known (see [37]) that the set of classical knots is aproper subset of the set of welded knots, and hence a proper subset of virtual knots.
Some invariants of classical knots correspond to some local moves in the sensethat two classical knots have the same invariant if and only if they are related by afinite sequence of the local moves; see e.g. [34, Section 2.8]. For example, the Arf
invariant of a classical knot corresponds to pass moves [19, 20]. It is important tostudy such correspondence because it reveals a relationship between algebraic andgeometric structures in classical knot theory.
From this point of view, there are many problems according to which family ofknots, which invariant of knots, and which local moves for knots we choose. For
example, the delta move, pass move, and sharp move are known to be unknotting

operations for welded knots [40], but not unknotting operations for virtual knots[41].

\tilde{I^\backsla h}\gam a_{)\nearow}rightarow/\backsla h\frac{1} {\prime_{\backsla h}delta moverightar owar ow^{\upar ow\upar ow 1 }arrowrightar owar ow^{|11\upar ow}

arrow| \downarrow 1

sharp move

pass move

Problem 2.1. Find invariants of a \mu ‐component virtual link (\mu\geq 1) corresponding
to the delta move.

Problem 2.2. Find invariants of a \mu ‐component virtual link (\mu\geq 1) corresponding
to the pass move.
Problem 2.3. Find invariants of a \mu ‐component virtual link (\mu\geq 1) corresponding
to the sharp move.
Problem 2.4. Find invariants of a \mu ‐component welded link (\mu\geq 2) corresponding
to the delta move.

Problem 2.5. Find invariants of a \mu ‐component welded link (\mu\geq 2) corresponding
to the pass move.
Problem 2.6. Find invariants of a \mu ‐component welded link (\mu\geq 2) corresponding
to the sharp move.
In virtual knot theory, there are several invariants such as the n ‐writhe (n\neq 0) ,the writhe polynomial, the odd writhe, the r ‐covering (r\geq 0, r\neq 1)[29] , and theJones polynomial.
3Department of Mathematics, Kobe University, Rokkodai‐cho 1‐1, Nada‐ku, Kobe 657‐8501, Japan
Email address: shin@math.kobe‐u.ac.jp5

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Problem 2.7. Find local moves for a virtual knot corresponding to the n ‐writhe(n\neq 0).

Problem 2.8. Find local moves for a virtual knot corresponding to the r ‐covering(r\geq 0, r\neq 1).

Problem 2.9. Find local moves for a \mu ‐component virtual link (\mu\geq 1) correspond‐
ing to the Jones polynomial.
It is known that the odd writhe of a virtual knot corresponds to a local movecalled the \Xi ‐move [41] and the writhe polynomial corresponds to a local move called
the shell move (given in our talk of this conference). We find several invariants
corresponding to the shell move in the case of a 2‐component virtual link [30]. In
the figure, the real crossings with the same label have the same crossing information.

rightarrow--- ‐move

Problem 2.10. Find invariants for a \mu ‐component virtual link (\mu\geq 2) correspond‐
ing to the :‐move.
Problem 2.11. Find invariants for a \mu ‐component virtual link (\mu\geq 3) correspond‐
ing to the shell move.
There is known no skein relation for the odd writhe and writhe polynomial of avirtual knot.

Problem 2.12. Find a skein relation for the odd writhe of a virtual knot.

Problem 2.13. Find a skein relation for the writhe polynomial of a virtual knot.

3

Rectilinear spatial complete graphs(Ryo Nikkuni)4
An embedding f of a finite graph G into \mathbb{R}^{3} is called a spatial embedding of G,
and the image f(G) is called a spatial graph of G . We call a subgraph \gamma of G
homeomorphic to the circle a cycle of G , and also call a k ‐cycle if it contains exactly
k edges. We denote the set of all k ‐cycles of G by \Gamma_{k}(G) , and the set of all pairs of
two disjoint cycles of G consisting of a k ‐cycle and an l ‐cycle by \Gamma_{k,l}(G) . For a cycle\gamma (resp. a pair of disjoint cycles \lambda ) and a spatial embedding f of G, f(\gamma) (resp.

f(\lambda)) is none other than a knot (resp. a 2‐component link) in f(G) . For a cycle \gamma

of G containing all vertices of G , we call f(\gamma) a Hamiltonian knot in f(G) .

67-8585,Japan4
Suginami-ku,
fMa.

jppukuji,Department otwcuTokyo
tahematil cs,School o
Email:nick@lab.

c.

fArts

and Sciences, Tokyo Woman’s Christian University, 2‐6‐1 Zem‐
6

123
Let K_{n} be the complete graph on n vertices, that is the graph consisting of nvertices such that each pair of its distinct vertices is connected by exactly one edge.
A spatial embedding f_{r} of K_{n} is said to be rectilinear if for any edge e of K_{n}, f_{r}(e)is a straight line segment in \mathb {R}^{3} . Such an embedding can be constructed by taking nvertices of K_{n} on the moment curve (t, t^{2}, t^{3}) in \mathbb{R}^{3} and connecting every pair of two

distinct vertices by a straight line segment, see Figure 4 for n=6,7 (we say such a
rectilinear spatial graph of K_{n} is standard). As a consequence of generalizations of
the Conway‐Gordon theorems [8], Morishita‐Nikkuni showed the following formula.
Theorem ([26]). Let n\geq 6 be an integer. For any rectilinear spatial embedding f_{r}of K_{n} , we have\sum_{\gamma\in\Gamma_{n}(K_{n}) a_{2}(f_{r}(\gamma) =\frac{(n-5)!}{2} ( \sum_{\lambda\in\Gam a_{3, }(K_{n}) lk (f_{r}(\lambda))^{2}- (\begin{ar y}{l n -1 5 \end{ar y}) ),where lk denotes the linking number, and a_{2} denotes the second coefficient of the
Conway polynomial.

fr(K_{6}) f_{r}(K_{7})Figure 4:Standard rectilinear spatial graphs of K_{n}(n=6,7)Note that every polygonal 2‐component link with exactly six sticks is either atrivial link or a Hopf link. Thus \sum_{\lambda\in\Gamma_{3,3}(K_{n})} lk (f_{r}(\lambda))^{2} coincides with the numberof “triangle‐triangle” Hopf links in f_{r}(K_{n}) . The original Conway‐Gordon theorem
for K_{6} implies that \sum_{\lambda\in\Gamma_{3,3}(K_{n})} lk (f_{r}(\lambda))^{2} is greater than or equal to the number ofsubgraphs of K_{n} isomorphic to K_{6} , that is equal to (\begin{ar y}{l n 6 \end{ar y}) . On the other hand, it is
known that every rectilinear spatial graph of K_{6} contains at most three Hopf links[17, 16, 31]. This implies that \sum_{\lambda\in\Gamma_{33}(K_{n})} lk (f_{r}(\lambda))^{2} is less than or equal to 3 (\begin{ar y}{l n 6 \end{ar y}) .
Thus by the theorem, we have the folíowing evaluations of the “algebraic” number
of Hamiltonian knots in every rectilinear spatial graph of K_{n}.

Corollary ([26]). Let n\geq 6 be an integer. For any rectilinear spatial embedding f_{r}of K_{n} , we have\frac{(n-5)(n-6)(n-1)!}{2\cdot 6!}\leq\sum_{\gamma\in\Gamma_{n}(K_{n})}a_{2} (f_{r}(\gamma) \leq\frac{3(n-2)(n-5)(n-1)!}{2\cdot 6!}.
7

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The lower bound in the corollary is sharp for arbitrary n\geq 6[26] . Actually thestandard rectilinear spatial graph of K_{n} realizes the sharp lower bound. In the caseof n=6 , the upper bound 1 is also sharp. On the other hand, the upper bound in

the case of n=7 is 15, but according to a computer search in [18], there seems to
be no rectilinear spatial embedding f_{r} of K_{7} such that \sum_{\gamma\in\Gamma_{7}(K_{7})}a_{2}(f_{r}(\gamma))=13,15.
This strongly suggests that the upper bound in the corollary is not sharp.

Problem 3.1 (R. Nikkuni). Determine the sharp upper bound of \sum_{\gamma\in\Gamma_{n}(K_{n})}a_{2}(f_{r}(\gamma))

for all rectilinear spatial embeddings f_{r} of K_{n} for each n\geq 7.

By the above mentioned theorem, Problem 3.1 is equivalent to the following
problem.

Problem 3.2 (R. Nikkuni). Determine the maximum number of triangle‐triangle
Hopf links in f_{r}(K_{n}) for all rectilinear spatial embeddings f_{r} of K_{n} for each n\geq 7.

4Instanton Floer theory for 3‐manifolds and the homology
cobordism group of integral homology 3‐spheres(Yuta Nozaki, Kouki Sato, Masaki Taniguchi)
Instanton Floer theory

The instanton Floer homology group I_{*}(Y) is an invariant of an oriented integral

homology 3‐sphere Y introduced by Floer [13]. The group I_{*}(Y) is an analog of

infinite dimensional Morse homology with respect to the Chern‐Simons functional.
We denote by \Omega^{1}(Y)\otimes \mathfrak{s}u(2) the set of \mathfrak{s}u(2) ‐valued 1‐forms. The Chern‐Simons
functional cs(a) is given by

cs(a):= \frac{1}{8\pi^{2} \int_{Y} (a \wedge da+\frac{2}{3}a\wedge a\wedge a)Tr.

If we fix a Riemann metric g on Y , one can consider the formal gradient of cs withrespect to an L^{2} ‐metric. There is a large symmetry on \Omega^{1}(Y)\otimes su(2) which is called
null‐homotopic gauge symmetry defined by\mathcal{G}_{Y} :=\{g\in Map(Y, SU(2))|\deg(g)=0\},
where the degree is the mapping degree. The action is given by a\cdot g :=g^{-1}dg+g^{-1}ag.
One can see the map cs descends to the map
cs:\mathcal{B}_{Y}:=(\Omega^{1}(Y)\otimes \mathfrak{s}u(2) /\mathcal{G}_{y}arrow \mathbb{R}.

The set of solution to F(a)=0 in \mathcal{B}_{y} is denoted by R_{Y} . Some parts of R_{Y} correspondto critical values of cs. In a good situation, the chains are generated by some partof R_{Y} . The differential is defined by counting the solution to the gradient flow of
cs. The gradient flows correspond to solutions to ASD‐equation on Y\cross \mathbb{R}.
Although the group I_{*}(Y) is the first example of Floer homology groups for 3‐
manifolds, even the following fundamental problem is still open.
8

125Problem 4.1. Construct a well‐defined equivariant instanton Floer homology for
SU(2) ‐bundles on all 3‐manifolds.
The main problems are to deal with the reducible solutions and the dependenceof perturbations. For example, the dependence of perturbations made in [2] is still
open. We also mention a problem related to Floer homotopy types introduced in [7].

It is known that several Floer theoretical invariants of 3 or 4‐manifolds are obtained

as the singular homology of some topological objects, and the stable homotopy typesof the topological objects themselves are invariants of 3 or 4‐manifolds. Thus, thehomotopy type is called the Floer homotopy type ([24, 22]). For the group I_{*}(Y) , its
Floer homotopy type has been unknown.

Problem 4.2. Construct a Floer homotopy type of I_{*}(Y) .
The main problems to define an instanton Floer homotopy type are related to the
bubble phenomena and the existence of structures of manifolds with corners on thecompactification of moduli spaces of trajectories and the framings. If the problem
is solved, we can apply a generalized cohomology theory and obtain a family ofinvariants.

Homology cobordism group

Two oriented integral homology 3‐spheres Y_{1}, Y_{2} are homology cobordant if there
exists a cobordism W from Y_{1} to Y_{2} with

H_{*}(W;\mathbb{Z})\cong H_{*}(S^{3}\cross I;\mathbb{Z}) .

This is anequivalence relation on the set of oriented integral homology 3‐spheres, and thequotient set \Theta^{3} equipped with the connected sum operation is an abelian groupcalled the homology cobordism group. It is known [12, 14] that \Theta^{3} contains a \mathbb{Z}^{\infty}

subgroup, which is generated by Seifert homology 3‐spheres. The group \Theta^{3} has
further been studied since various Floer theory for 3‐manifolds were established,
while we still have several elementary open problems. For instance, the following
question is open.

Question 4.3. Denote by \Theta_{S}^{3} the subgroup of \Theta^{3} generated by Seifert homology
3‐spheres. Then, is the quotient group \Theta^{3}/\Theta_{S}^{3} non‐trivial!?
Here we mention that the above question is related to our invariant r_{+}:\Theta^{3}arrow\mathbb{R}_{\geq 0}\cup\{\infty\} ; for details of r+ , see [32]. In fact, the value r_{+}(Y) is contained in cs(R_{Y}) ,and if Y is a linear combination of Seifert homology 3‐spheres, then cs(R_{Y})\subset \mathbb{Q}.

These imply that if a homology 3‐sphere Y has irrational r+ , then its homology
cobordism class [Y] is not contained in \Theta_{S}^{3} . On the other hand, by Mathematica,
the authors estimated the value r_{+}(S_{1/2}^{3}(5_{2}^{*})) with an error of at most 10^{-46} , whereS_{1/2}^{3}(5_{2}^{*}) denotes the 3‐manifold obtained by 1/2‐surgery on the mirror of the knot
S_{1/2}^{3}(5_{2}^{*}) is a hyperbolic 3‐manifold (see [5]). The result seems to
imply that r_{+}(S_{1/2}^{3}(5_{2}^{*})) is irrational. If the value r_{+}(S_{1/2}^{3}(5_{2}^{*})) is truly irrational,
then we can conclude that
[S_{1/2}^{3}(5_{2}^{*})]\not\in\Theta_{S}^{3}.
Question 4.4 (Y. Nozaki, K. Sato, M. Taniguchi). Is the value r_{+}(S_{1/2}^{3}(5_{2}^{*})) irra‐
5_{2} , noting thattional;?

9

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The method of our computation is based on Kirk and Klassen’s formula of cs givenby the integration along a path in the space of irreducible SL(2, \mathbb{C}) ‐representations.
To obtain the approximate value of r+ , we use a description of the space of SL(2, \mathbb{C}) ‐representations of \pi_{1}(S^{3}\backslash 5_{2}) , as in [36], in terms of a Riley polynomial \phi(t, u)\in\mathbb{Z}[t^{\pm 1}, u] with \deg_{u}\phi=3 . Then we can explicitly solve the equation \phi(u, t)=0

with respect to u and use the solutions to compute r+\cdot However, Riley polynomials\phi(t, u) of 2‐bridge knots K might be of degree larger than 4. In this case, one cannot
solve \phi(t, u)=0 in general.

Problem 4.5 (Y. Nozaki, K. Sato, M. Taniguchi). In the case \deg_{u}\phi>4 , give amethod to compute an approximate value of r_{+}(S_{1/n}^{3}(K)) .

Note that, in principle, we can compute approximate values by dividing a path into
shorter paths.

5

The AMU Conjecture for self‐homeomorphisms of sur‐faces and the volume conjecture for 3‐manifolds(Tian Yang)
According to Nielsen‐Thurston’s classification of the elements of the mappingclass group of surfaces, every irreducible orientation preserving self‐homeomorphismof a surface of finite type is either periodic (of finite order) or pseudo‐Anosov (pre‐serving two transverse measure laminations). Here a self‐homeomorphism being
irreducible means that it does not restrict of a proper subsurface. In [1], Andersen‐
Masbaum‐Ueno made the following

Conjecture 5.1 (J. E. Andersen, G. Masbaum, K. Ueno [1]). Let \Sigma be a orientablesurface of finite type, let \phi be a pseudo‐Anosov self‐homeomorphism of \Sigma , and let\{\rho_{r}\}_{r} be the sequence of the Turaev‐ Viro representations of the mapping class groupof \Sigma . Then for r sufficiently large, \rho_{r}([\phi]) is a linear transformation of infinite order.
Combined with the fact that the image of a finite order element under any grouprepresentation is of finite order, the AMU Conjecture essentially claims that thesequence of Turaev‐Viro representations of the mapping class groups respects theNielsen‐Thurston classification. The similar conjecture can be made for the Reshetikhin‐
Turaev representations, which are a sequence of projective representations of map‐ping class group of surfaces. The AMU conjecture is known to be true for punctured

spheres [1, 11] and the once‐punctured torus [38]. Recently, Marché‐Santharoubane [25]related the Turaev‐Viro representations to representations of the fundamental groupof surfaces, and provide an efficient algorithm of determining whether an element of
the fundamental group can be represented by a simple closed curve on the surface,assuming that the AMU Conjecture is true.

Observed by Santharoubane [39] (see also Detcherry‐Kalfagianni [10]), the AMU

Conjecture is a consequence of the following a weaker version of the Volume Con‐jecture of Chen‐Yang [6].
10127Conjecture 5.2 (a weaker version of the volume conjecture of Q. Chen and T.
Yang [6]). Let M be a hyperbolic 3‐manifold with finite volume, and let TV_{r}(M;q)
be its r‐th Turaev‐ Viro invariant at the root of unity q . Then for r running over all
the odd integers,

1 \dot{ \imath} m\dot{ \imath} nf\frac{1}{r}\ln TV_{r}(M;e^{\frac{2\pi }{r} )r \mapsto\infty>0.

The relationship between the two conjectures mentioned above is given by the under‐
lying TQFTs. Roughly speaking, the mapping cylinder MC_{\phi} of \phi can be considered
as a cobordism from \Sigma to itself. Hence for each r , the Turaev‐Viro TQFT assigns
MC_{\phi} a linear map, which is exactly \rho_{r}([\phi]) by the construction of the Turaev‐Viro
representation. By the TQFT axioms, the trace of \rho_{r}([\phi]) equals to the Turaev‐
Viro invariant TV_{r}(M_{\phi}) of the mapping torus M_{\phi} of \phi . Since \phi is pseudo‐Anosov,
Thurston’s result shows that M_{\phi} is hyperbolic. Then Conjecture 5.2 implies that
TV_{r}(M) grows at least exponentially at particular roots of unity. On the other
hand, if \rho_{r}([\phi]) was of finite order, the each of its eigenvalues should be a root ofunity. As a consequence, the trace of \rho_{r}([\phi]) is at most the dimension of the TQFT
vector space of \Sigma , which by the Verlinde formula is only a polynomial in r . That isa contradiction.

In a recent work [9], Detcherry‐Kalfagianni showed that the behavior of theTuraev‐Viro invariant is “similar to” that of the hyperbolic volume, in the sensethat it does not increase under Dehn‐fillings. Therefore, if one could prove Conjec‐
ture 5.2 for a 3‐manifold M , then Conjecture 5.2 is automatically true for all the

3‐manifolds obtained from M by removing a link inside it. Recently, Ohtsuki [35]and Belletti‐Detcherry‐Kalfagianni‐Yang [3] proved the Volume Conjecture of Chen‐
Yang for infinite families of 3‐manifolds, including the closed hyperbolic ones ob‐
tained by doing integral Dehn‐fillings along the figure‐8 knot and the fundamental
shadow link complements. Therefore, Conjecture 5.2 hold for all the 3‐manifolds
obtained from the examples mentioned above by remove a link inside them, and the
AMU Conjecture holds for the fibered ones obtained from those examples by doing
the same operation. From the discussions above, one sees that a solution to thefollow problem will give a final solution to the AMU Conjecture, at least for all the
punctured surfaces.

Problem 5.3 (T. Yang). Find a family of 3‐manifolds for which Conjecture 5.2
holds, and by removing links from which one gets all the pseudo‐Anosov mapping
torus of all punctured surfaces.

6

The mapping class group of a surface and the quantum
invariants of integral homology 3‐spheres(Shunsuke Tsuji)
Let \Sigma_{g,1} be a surface of genus 1 with a connected non‐empty boundary. We con‐sider the lower central series \{F^{n}\pi_{1}(\Sigma_{g,1}, *)\}_{n\geq 1} of \pi_{1}(\Sigma_{g,1}, *) where *\in\partial\Sigma_{g,1} , de‐fined by F^{1}\pi_{1}(\Sigma_{g,1}, *)^{def}=\pi_{1}(\Sigma_{g,1}, *) and F^{n+1}\pi_{1}(\Sigma_{g,1}, *)=def[\pi_{1}(\Sigma_{g,1}, *), F^{n}\pi_{1} (\Sigma_{g,1}, *)].
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We denote by \mathcal{M}(\Sigma_{g,1}) the mapping class group of \Sigma_{g,1} and by \mathcal{I}(\Sigma_{g,1}) the Torelligroup, which is the kernel of the action of \mathcal{M}(\Sigma_{g,1}) on the homology group of\Sigma_{g,1} . We can define two filtrations \{\mathcal{I}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} and \{\mathcal{M}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} . The first\{\mathcal{I}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} is the lower central series, defined by \mathcal{I}^{(1)}(\Sigma_{g,1})def=\mathcal{I}(\Sigma_{g,1}) and\mathcal{I}^{(n+1)}(\Sigma_{g,1})=def[\mathcal{I}(\Sigma_{g,1}),\mathcal{I} ^{(n)}(\Sigma_{g,1})] . The second \{\mathcal{M}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} is the Johnson fil‐tration, satisfying \mathcal{M}^{(n)}(\Sigma_{g,1}) is the kernel of the action of \mathcal{M}(\Sigma_{g,1}) on
F^{1}\pi_{1}(\Sigma, *)/F^{n+1}\pi_{1}(\Sigma, *).

We denote byz^{s1_{2}}(M)=1+z_{1}^{s1_{2}}(M)(q-1)+z_{2}^{s1_{2}}(M)(q-1)^{2}+\cdots
the invariant of an integral homology 3‐sphere M defined by T. Ohtsuki [33]. We fix
a Heegaard splitting of S^{3}=H_{g}^{+} \bigcup_{\iota}H_{g}^{-} , where H_{g}^{+} and H_{g}^{-} are handle bodies of genus

is a diffeomorphism from \partial H_{g}^{+} to \partial H_{g}^{-} . We denote M( \psi)def=H_{g}^{+}\bigcup_{\psi\circ\iota}H_{g}^{-}
for \psi\in \mathcal{M}(\Sigma_{g,1}) , where we consider \Sigma_{g,1} as a submanifold of \partial H_{g}^{+}.
g and

\iota

Then we obtain z_{i}^{s1_{2}}(M(\psi))=0 if \psi\in \mathcal{I}^{(2i+1)}(\Sigma_{g,1}) for any i . In the caseof the Johnson filtration \{\mathcal{M}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} , there exists \psi\in \mathcal{M}^{(3)}(\Sigma_{g,1}) satisfyingz_{1}^{s1_{2}}(M(\psi))\neq 0 . S. Morita [27] constructs the core of the Casson invariant d :\mathcal{M}^{(2)}(\Sigma_{g,1})arrow \mathbb{Z} where z_{1}^{s1_{2}}(M(\psi))=0 if \psi\in \mathcal{I}^{(3)}(\Sigma_{g,1})\cap kerd . In other words,
we can define z_{1}^{s1_{2} using the Johnson homomorphisms and the core of the Casson
invariant.

Conjecture 6.1 (S. Morita). For any i\in \mathbb{Z}_{\geq 1}, z_{i}^{s{\imath}_{2}}(M(\psi))=0if\psi\in \mathcal{M}^{(2i+1)}(\Sigma_{g,1}) \capkerd.

By definition, if i=1 , the conjecture is true.

Morita-Sakasai- Suzuki [ 28] prove thatthe conjecture is true if i=2,3.
We can also definez^{s1_{N}}(M)=1+z_{1}^{s1_{N}}(M)(q-1)+z_{2}^{s1_{N}}(M)(q-1)^{2}+\cdots
using the s1_{N} ‐quantum group in [21].
Conjecture 6.2 (S. Morita, S. Tsuji). Fix an integer N larger than 2. For any
i\in \mathbb{Z}_{\geq 1}, z_{i}^{s1_{N}}(M(\psi))=0 if \psi\in \mathcal{M}^{(2i+1)}(\Sigma_{g,1})\cap kerd.
By definition, if i=1 , the conjecture is true. Morita‐Sakasai‐Suzuki [28] also provethat the conjecture is true if i=2,3.
We introduce an approach of the conjectures using skein algebras. Let\{\mathcal{M}_{Kauffman}^{(n)}(\Sigma_{g,1})\}_{n\geq 1} be a filtration of the Torelli group defined using the Kauff‐man bracket skein algebra. For any i\in \mathbb{Z}_{\geq 1} , we have z_{i}^{s1_{2}}(M(\psi))=0 if \psi\in\mathcal{M}_{Kauffman}^{(2i+1)}(\Sigma_{g,1}) . If \mathcal{M}^{(i)}(\Sigma_{g,1})\cap kerd\subset \mathcal{M}_{Kauffman}^{(i)} (\Sigma_{g,1}) for any i , the first con‐jecture is true. Let \{\mathcal{M}_{HOMFLy-PT}^{()}(\Sigma_{g,1})\}_{n\geq 1} be a filtration of the Torelli groupdefined using the HOMFLY‐PT skein algebra. For any N and any i\in \mathbb{Z}_{\geq 1} , we havez_{i}^{s1_{N}}(M(\psi))=0 if \psi\in \mathcal{M}_{HOMFLY-PT}^{(2x+1)}(\Sigma_{g,1}) . We remark that \mathcal{M}^{(i)}(\Sigma_{g,1})\cap kerd\supset\mathcal{M}_{HOMFLY-PT}^{(i)}(\Sigma_{g,1}) . If \mathcal{M}^{(i)}(\Sigma_{g,1})\cap kerd=\mathcal{M}_{HOMFLY-PT}^{(i)} (\Sigma_{g,1}) for any i , the second

conjecture is true for any N.

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7

Positive flow‐spines and contact 3‐manifolds(Ippei Ishii, Masaharu Ishikawa, Yuya Koda, Hironobu Naoe)
In this section,

M always denotes a closed, oriented, smooth 3‐manifold.

(positive) contact structure on M is a transversely orientable 2‐plane fieldon M , given as the kernel of a 1‐form (called a contact form) \alpha on M , where asatisfies \alpha\wedge d\alpha>0 . The pair (M, \xi) is called a contact 3‐manifold. Two contact
A

structures \xi_{0} and \xi_{1} are said to be isotopic if there exists a 1‐parameter family of
contact structures connecting them. For a contact form \alpha , the Reeb vector field R_{\alpha}is defined by d\alpha(R_{\alpha}, \cdot)=0 and \alpha(R_{\alpha})=1 . We also call R_{\alpha} a Reeb vector field of
the contact structure \xi=ker\alpha . The flow generated by R_{\alpha} is called the Reeb flowof \alpha (or a Reeb flow of \xi ). A contact structure \xi is said to be overtwisted if there
exists a disk D embedded in M such that \partial D is everywhere tangent to \xi and theframing of D along \partial D coincides with that of \xi . Otherwise \xi is said to be tight.
A 2‐dimensional polyhedron P in M is called a flow‐spine if(1)

P is a spine, that is,M\backslash P is an open 3‐ball; and(2) there exists a non‐singular flow \Phi=\{\varphi_{t}\}_{t\in \mathbb{R} on M such that for each pointof P , there exists a positive chart (U;x, y, z) of M around the point such that
(U, U\cap P) is diffeomorphic (by an orientation‐preserving diffeomorphism) to
one of the four models shown in Figure 5, where the flow \Phi on U is generated
by the vector field \partial/\partial z.
Further, a flow‐spine P is said to be positive if P has at least one point of the modelof Figure 5 (iii) and has no point of the model of Figure 5 (iv). In the above setting,

we say that the flow \Phi is carried by P . A contact structure \xi on
supported by a flow‐spine P if a Reeb flow of \xi is carried by P.

M is said to bez_{L_{ar ow}^{y}

x

(i)

(ii)

(iii)

(iv)

Figure 5: The ıocal models of a flow‐spine.

Theorem (I. Ishii, M. Ishikawa, Y.Koda, H. Naoe). The map{positive flow‐spines of M}/isotopy

arrow{contact structures on M}/isotopythat takes a positive flow‐spine P (up to isotopy) to a contact structure \xi (up to
isotopy) whose Reeb flow is carried by P is a well‐defined surjective map.

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Problem 7.1 (I. Ishii, M. Ishikawa, Y.Koda, H. Naoe). Find moves for positive
flow‐spines so that the map{positive flow‐spines of M } /movesarrow {contact structures on M}/isotopy
induced from the surjection in the theorem is a bijection.

Apparently, an answer to the above problem completes to give a counterpart of thefamous Giroux correspondence [15]. In the Giroux correspondence, it is known thata contact 3‐manifold (M, \xi) is Stein fillable if and only if (M, \xi) admits a supporting
open book decomposition whose monodromy is a product of right‐handed Dehn
twists. In particular, \xi is tight in this case.

Problem 7.2 (I. Ishii, M. Ishikawa, Y.Koda, H. Naoe). Give a criterion for thetightness or Stein fillability of contact structures in terms of supporting positive
flow‐spines.
It is known that for any non‐singular flow \Phi on M , there exists a flow‐spine
carrying \Phi . Further, by the above mentioned theorem, a certain Reeb flow of any
contact manifold (M, \xi) is carried by a positive flow‐spine.

Question 7.3 (I. Ishii, M. Ishikawa, Y.Koda, H. Naoe). Is any Reeb flow of any
contact manifold (M, \xi) carried by a positive flow‐spine /?
A point of a flow‐spine

P whose neighborhood is shaped on the model(iii) inFigure 5 is called a vertex of P . The complexity c(M, \xi) of a contact 3‐manifold(M, \xi) is defined to be the minimum number of vertices of any positive flow‐spine
supporting \xi . Note that c is finite‐to‐one. The classification of contact 3‐manifolds
of complexity up to 3 is now in progress.

Problem 7.4 (I. Ishii, M. Ishikawa, Y.Koda, H. Naoe). ClassOfy the contact 3‐
manifolds of complexity 4.
In our classification, it seems that any positive flow‐spine with at most 3 vertices sup‐ports a tight contact structure. On the other hand, there exists a positive flow‐spineof S^{3} with 5 vertices supporting an overtwisted contact structure. It is interesting
to determine whether there is a positive flow‐spine with 4 vertices supporting an
overtwisted contact structure or not.

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