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Eiji Ogasa

Publications and source records attributed to Eiji Ogasa.

At least 19 recordsLinked to original sources

Exotic 4-manifolds and Khovanov-Lipshitz-Sarkar homotopy type

We introduce a new diffeomorphism invariant of smooth compact oriented 4-manifolds $X$ with a framed oriented 1-link $L$ in the boundary, where $L$ may be the empty set, and call it {\it Khovanov-Lipshitz-Sarkar skein lasagna homotopy type} or {\it KLS lasagna homotopy type} $\mathcal E^{LS}_0(X,L)$. Our invariant assigns to a smooth structure a stable homotopy type of a CW complex. Our new invariant is not weaker than KR lasagna module, which were defined by Morrison, Walker and Wedrich. For a pair $(X,L)$ such that $L\neq\emptyset$, our new invariant, KLS lasagna homotopy type, is stronger than the Khovanov-Rozansky $\mathfrak{gl}_2$ skein lasagna modules or KR lasagna modules.

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New invariants for virtual knots via spanning surfaces

We define three different types of spanning surfaces for knots in thickened surfaces. We use these to introduce new Seifert matrices, Alexander-type polynomials, genera, and a signature invariant. One of these Alexander polynomials extends to virtual knots and can obstruct a virtual knot from being classical. Furthermore, it can distinguish a knot in a thickened surface from its mirror up to isotopy. We also propose several constructions of Heegaard Floer homology for knots in thickened surfaces, and give examples why they are not stabilization invariant. However, we can define Floer homology for virtual knots by taking a minimal genus representative. Finally, we use the Behrens-Golla $δ$-invariant to obstruct a knot from being a stabilization of another.

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Quantum Invariants of Links and 3-Manifolds with Boundary defined via Virtual Links

We introduce new topological quantum invariants of compact oriented 3-manifolds with boundary where the boundary is a disjoint union of two identical surfaces. The invariants are constructed via surgery on manifolds of the form $F \times I$ where $I$ denotes the unit interval. Since virtual knots and links are represented as links in such thickened surfaces, we are able also to construct invariants in terms of virtual link diagrams (planar diagrams with virtual crossings). These invariants are the first meaningful, nontrivial, and calculable examples of quantum invariants of 3-manifolds with non-vacuous boundary. We give a new invariant of classical links in the 3-sphere in the following sense: Consider a link $L$ in $S^3$ of two components. The complement of a tubular neighborhood of $L$ is a manifold whose boundary consists in two copies of a torus. Our invariants apply to this case of bounded manifold and give new invariants of the given link of two components. Invariants of knots are also obtained.

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Quantum Invariants of Links and 3-Manifolds with Boundary defined via Virtual Links: Calculation of some examples

In the prequel of this paper, Kauffman and Ogasa introduced new topological quantum invariants of compact oriented 3-manifolds with boundary where the boundary is a disjoint union of two identical surfaces. The invariants are constructed via surgery on manifolds of the form $F \times I$ where $I$ denotes the unit interval. Since virtual knots and links are represented as links in such thickened surfaces, we are able also to construct invariants in terms of virtual link diagrams (planar diagrams with virtual crossings). These invariants are new, nontrivial, and calculable examples of quantum invariants of 3-manifolds with non-vacuous boundary. Since virtual knots and links are represented by embeddings of circles in thickened surfaces, we refer to embeddings of circles in the 3-sphere as {\it classical links}. Classical links are the same as virtual links that can be represented in a thickened 2-sphere and it is a fact that classical links, up to isotopy, embed in the collection of virtual links taken up to isotopy. We give a new invariant of classical links in the 3-sphere in the following sense: Consider a link $L$ in $S^3$ of two components. The complement of a tubular neighborhood of $L$ is a manifold whose boundary consists in two copies of a torus. Our invariants apply to this case of bounded manifold and give new invariants of the given link of two components. Invariants of knots are also obtained. In this paper we calculate the topological quantum invariants of some examples explicitly. We conclude from our examples that our invariant is new and strong enough to distinguish some classical knots from one another. We also explain how different Our topological quantum invariants of 3-manifolds with boundary and the Reshetikhin-Turaev invariants are. (See the body for detail).

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Khovanov-Lipshitz-Sarkar homotopy type for links in thickened higher genus surfaces

We discuss links in thickened surfaces. We define the Khovanov-Lipshitz-Sarkar stable homotopy type and the Steenrod square for the homotopical Khovanov homology of links in thickened surfaces with genus$>1$. A surface means a closed oriented surface unless otherwise stated. Of course, a surface may or may not be the sphere. A thickened surface means a product manifold of a surface and the interval. A link in a thickened surface (respectively, a 3-manifold) means a submanifold of a thickened surface (respectively, a 3-manifold) which is diffeomorphic to a disjoint collection of circles. Our Khovanov-Lipshitz-Sarkar stable homotopy type and our Steenrod square of links in thickened surfaces with genus$>1$ are stronger than the homotopical Khovanov homology of links in thickened surfaces with genus$>1$. It is the first meaningful Khovanov-Lipshitz-Sarkar stable homotopy type of links in 3-manifolds other than the 3-sphere. We point out that our theory has a different feature in the torus case.

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Make your Boy surface

This is an introductory article about the Boy surface. Boy found 1901 that $\mathbb{R}P^2$ can be immersed into $\mathbb{R}^3$, and published it. (The image of) the immersion is called the Boy surface after Boy's discovery. We have created a way to construct the Boy surface by using a pair of scissors, a piece of paper, and a strip of scotch tape. In this article we introduce the way. Furthermore, we make a movie to show the paper-craft actually, and put it in a website. One can find the website by typing in the author's name or the title of this article in the search engine.

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A spinning construction for virtual 1-knots and 2-knots, and the fiberwise and welded equivalence of virtual 1-knots

We succeed to generalize spun knots of classical 1-knots to the virtual 1-knot case by using the `spinning construction'. That, is, we prove the following: Let $Q$ be a spun knot of a virtual 1-knot $K$ by our method. The embedding type $Q$ in $S^4$ depends only on $K$. Furthermore we prove the following: The submanifolds, $Q$ and the embedded torus made from $K,$ defined by Satoh's method, in $S^4$ are isotopic. We succeed to generalize the above construction to the virtual 2-knot case. Note that Satoh's method says nothing about the virtual 2-knot case. Rourke's interpretation of Satoh's method is that one puts `fiber-circles' on each point of each virtual 1-knot diagram. If there is no virtual branch point in a virtual 2-knot diagram, our way gives such fiber-circles to each point of the virtual 2-knot diagram. We prove the following: If a virtual 2-knot diagram $α$ has a virtual branch point, $α$ cannot be covered by such fiber-circles. We obtain a new equivalence relation, the $\mathcal E$-equivalence relation of the set of virtual 2-knot diagrams, by using our spinning construction. We prove that there are virtual 2-knot diagrams that are virtually nonequivalent but are $\mathcal E$-equivalent. Although Rourke claimed that two virtual 1-knot diagrams $α$ and $β$ are fiberwise equivalent if and only if $α$ and $β$ are welded equivalent, we state that this claim is wrong. We prove that two virtual 1-knot diagrams $α$ and $β$ are fiberwise equivalent if and only if $α$ and $β$ are rotational welded equivalent.

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Brieskorn submanifolds, Local moves on knots, and knot products

We prove the following: Let $2p + 1$ be no less than 5 and $p$ be a natural number. Let $K$ and $J$ be closed, oriented, $(2p+1)$-dimensional connected, $(p-1)$-connected, simple submanifolds of the standard $(2p+3)$-sphere. Then $K$ is equivalent to $J$ if and only if a Seifert matrix associated with a simple Seifert hypersurface for $K$ is $(-1)^p$-$S$-equivalent to that for $J$. We also discuss the $2p+1=3$ case. This result implies one of our main results: Let $μ$ be a natural number. A 1-link $A$ is pass-move equivalent to a 1-link $B$ if and only if the knot product of $A$ and $μ$ copies of the Hopf link is $(2μ+1, 2μ+1)$-pass-move equivalent to that of B and $μ$ copies of the Hopf link. It also implies the other of them: Two-fold cyclic suspension commutes with the performance of the twist move for spherical $(2k+1)$-knots ($2k+1>4$). Furthemroe we prove the following: Let $2p+1$ be no less than 5 and p be a natural number. Let $K$ be a closed oriented $(2p+1)$-dimensionalsubmanifold of the standard $(2p+3)$-sphere. Then $K$ is a Brieskorn submanifold if and only if $K$ is connected, $(p-1)$-connected, simple and has a $(p+1)$-Seifert matrix associated with a simple Seifert hypersurface that is $(-1)^p$-$S$-equivalent to a Kauffman-Neumann-type, or a KN-type (See the body of the paper for a definition.) We also discuss the $2p+1=3$ case.

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Intersectional pairs of $n$-knots, local moves of $n$-knots, and their associated invariants of $n$-knots

Let $n$ be an integer$\geqq0$. Let $S^{n+2}_1$ (respectively, $S^{n+2}_2$) be the $(n+2)$-sphere embedded in the $(n+4)$-sphere $S^{n+4}$. Let $S^{n+2}_1$ and $S^{n+2}_2$ intersect transversely. Suppose that the smooth submanifold, $S^{n+2}_1 \cap S^{n+2}_2$ in $S^{n+2}_i$ is PL homeomophic to the $n$-sphere. Then $S^{n+2}_1$ and $S^{n+2}_2$ in $S^{n+2}_i$ is an $n$-knot $K_i$. We say that the pair $(K_1,K_2)$ of n-knots is realizable. We consider the following problem in this paper. Let $A_1$ and $A_2$ be n-knots. Is the pair $(A_1,A_2)$ of $n$-knots realizable? We give a complete characterization.

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The intersection of three spheres in a sphere and a new application of the Sato-Levine invariant

Take transverse immersions f from a disjoint unin of the three 4-spheres $S^4_1$, $S^4_2$, and $S^4_3$ into $S^6$ with the following properties: (1) The restriction of $f$ to $S^4_i$ is an embedding, (2) The intersection of $f(S^4_i)$ and $f(S^4_j)$ is not empty and connected, (3)The intersection among $f(S^4_1)$, $f(S^4_2)$, and $f(S^4_3)$ is not empty. Then we obtain three surface-links $L_i=(S^4_i\cap S^4_j, S^4_i\cap S^4_k)$ in $S^4_i$, where $(i,j,k)=(1,2,3), (2,3,1), (3,1,2).$ We prove that, we have the equality $β(L_1)+β(L_2)+β(L_3)=0$, where $β(L_i)$ is the Sato-Levine invariant of $L_i$, if all $L_i$ are semi-boundary links.

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Introduction to high dimensional knots

This is an introductory article on high dimensional knots for the beginners. High dimensional knot theory is an exciting field. It is a field of knot theory, which is one of topology and is connected with many ones. In this article we use few literal expressions, equations, functions, etc. We barely suppose that the readers have studied manifolds, homology theory, or topics beyond them. Is there a nontrivial high dimensional knot? We first answer this question. After that, we explain local moves on high dimensional knots and the projections of high dimensional knots.

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Local moves on knots and products of knots II

We use the terms, knot product and local move, as defined in the text of the paper. Let $n$ be an integer$\geqq3$. Let $\mathcal S_n$ be the set of simple spherical $n$-knots in $S^{n+2}$. Let $m$ be an integer$\geqq4$. We prove that the map $j:\mathcal S_{2m}\to\mathcal S_{2m+4}$ is bijective, where $j(K)=K\otimes$Hopf, and Hopf denotes the Hopf link. Let $J$ and $K$ be 1-links in $S^3$. Suppose that $J$ is obtained from $K$ by a single pass-move, which is a local-move on 1-links. Let $k$ be a positive integer. Let $P\otimes^kQ$ denote the knot product $P\otimes\underbrace{Q\otimes...\otimes Q}_k$. We prove the following: The $(4k+1)$-dimensional submanifold $J\otimes^k{\rm Hopf}$ $\subset S^{4k+3}$ is obtained from $K\otimes^k{\rm Hopf}$ by a single $(2k+1,2k+1)$-pass-move, which is a local-move on $(4k+1)$-submanifolds contained in $S^{4k+3}$. See the body of the paper for the definitions of all local moves in this abstract. We prove the following: Let $a,b,a',b'$ and $k$ be positive integers. If the $(a,b)$ torus link is pass-move equivalent to the $(a',b')$ torus link, then the Brieskorn manifold $Σ(a,b,\underbrace{2,...,2}_{2k})$ is diffeomorphic to $Σ(a',b',\underbrace{2,...,2}_{2k})$ as abstract manifolds. Let $J$ and $K$ be (not necessarily connected or spherical) 2-dimensional closed oriented submanifolds in $S^4$. Suppose that $J$ is obtained from $K$ by a single ribbon-move, which is a local-move on 2-dimensional submanifolds contained in $S^4$. Let $k$ be an integer$\geq2$. We prove the following: The $(4k+2)$-submanifold $J\otimes^k{\rm Hopf}$ $\subset S^{4k+4}$ is obtained from $K\otimes^k{\rm Hopf}$ by a single $(2k+1,2k+2)$-pass-move, which is a local-move on $(4k+2)$-dimensional submanifolds contained in $S^{4k+4}$.

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Singularities of the projections of $n$-dimensional knots

Let n be aninteger>4. There is a smoothly knotted n-dimensional sphere in (n+2)-space such that the singular point set of its projection in (n+1)-space consists of double points and that the components of the singular point set are two. (The sphere is knotted in the sense that it does not bound any embedded (n+1)-ball in (n+2)-space.) Furthermore, the projection is not the projection of any unknotted sphere in the (n+2)-space. There are two inequivalent embeddings of an n-manifold in the (n+2)-space such that the projection of one of these in (n+1)-space has no double points and the projection of the other has a connected embedded double point set.

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Link cobordism and the intersection of slice discs

It is well-known that all 2-knots are slice. Are all 2-links slice? This is an outstanding open question. In this paper we prove the following: For any 2-component 2-link (J,K)in the 4-sphere which bounds the 5-ball B^5, there is an embedded disc 2-disc D^2_J (respectively, D^2_K) in B^5 with the following properties: J (respectively K) bounds D^2_J (respectively, D^2_K). D^2_J and D^2_K intersect transversely. the intersection of D^2_J and D^2_K in D^2_J (respectively, D^2_K) is a trivial 1-knot.

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