Mikhail Kogan
Let $M$ be a compact oriented simply-connected manifold of dimension at least 8. Assume $M$ is equipped with a torsion-free semi-free circle action with isolated fixed points. We prove $M$ has a perfect invariant Morse-Smale function. The major ingredient in the proof is a new cancellation theorem for the invariant Morse theory.
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Murasugi sums can be defined as readily for Morse maps to the circle of (arbitrary) link complements in the 3-sphere as for fibrations over the circle of (fibered) link complements in the 3-sphere. As one application, I show that if a knot K has free genus m, then there is a Morse map from its complement to the circle (representing the relative homology class of a Seifert surface for K) with no more than 4m critical points.
We classify the path-components of the space of circle-valued Morse functions on compact surfaces: two Morse functions $f, g: M\to S^1$ belong to same path-component of this space if and only if they are homotopic and have equal numbers of critical points at each index.
We show that the Morse boundary of a right-angled Coxeter group may contain embedded circles that do not arise as the boundary of a Morse Fuchsian subgroup visible in the defining graph.
Non-singular extensions of circle-valued Morse functions
研究闭合定向曲面上的圈值Morse函数非奇点扩展条件，给出在 collar 邻域存在子浸入时的必要充分条件。
Perfect circle-valued Morse functions on hyperbolic 6-manifolds
本文首次构造了具有完美圆值Morse函数的双曲6流形，并由此得到双曲群中一个类型为F2而非F3的子群新例子。
Let A be an essential complex hyperplane arrangement in an n-dimensional complex vector space V. Let H denote the union of the hyperplanes, and M denote the complement to H in V. We develop the real-valued and circle-valued Morse theory for M and prove, in particular, that M has the homotopy type of a space obtained from a manifold fibered over a circle, by attaching cells of dimension n. We compute the Novikov homology of M for a large class of homomorphisms of the fundamental group of M to R.
Let N be a closed oriented k-dimensional submanifold of the (k+2)-dimensional sphere; denote its complement by C(N). Denote by x the 1-dimensional cohomology class in C(N), dual to N. The Morse-Novikov number of C(N) is by definition the minimal possible number of critical points of a regular Morse map f from C(N) to a circle, such that f belongs to x. In the first part of this paper we study the case when N is the twist frame spun knot associated to an m-knot K. We obtain a formula which relates the Morse-Novikov numbers of N and K and generalizes the classical results of D. Roseman and E.C. …
We show that an appropriate generalization of the oriented area function is a perfect Morse function on the space of three-dimensional configurations of an equilateral polygonal linkage with odd number of edges. Therefore cyclic equilateral polygons (which appear as Morse points) are interpreted as independent generators of the homology groups of the (decorated) configuration space.
Hyperbolic 4-manifolds with perfect circle-valued Morse functions
本文构造了具有完美圆值Morse函数的有限体积双曲4-流形，证明了存在无限多个此类流形，其具有有界数量的1-和3-把手分解及有界的Betti数。
Arrangements of small circles for Morse-Bott functions
本文提出一种通过归纳添加小圆构造圆排列的系统方法，将其与Morse-Bott函数及Reeb图联系起来，研究排列中区域坍缩图的局部变化。
The main theorem of the paper shows that a smooth manifold which is homeomorphic to S^2xS^2 and has nonvanishing Ozsvath-Szabo invariant does not admit a perfect Morse function. I am withdrawing the paper because it is unclear to me if such a manifold exists.
Let $M$ be a smooth connected orientable compact surface. Denote by $F(M,S^1)$ the space of all Morse functions $f:M\to S^1$ having no critical points on the boundary of $M$ and such that for every boundary component $V$ of $M$ the restriction $f|_{V}:V\to S^1$ is either a constant map or a covering map. Endow $F(M,S^1)$ with the $C^{\infty}$-topology. In this note the connected components of $F(M,S^1)$ are classified. This result extends the results of S. V. Matveev, V. V. Sharko, and the author for the case of Morse functions being locally constant on the boundary of $M$.
The Morse-Novikov number MN(L) of a smooth link L in the three-dimensional sphere is by definition the minimal possible number of critical points of a regular circle-valued Morse function on the link complement (the term regular means that the Morse function must have nice behaviour in a tubular neighbourhood of L). Novikov homology provides lower bounds for MN(L). In the present paper we introduce the notion of twisted Novikov homology, which allows to obtain better lower bounds for MN(L) than the usual Novikov homology. Our twisted Novikov homology is a module over the Novikov ring Z((t)) bu…
Characterizing $3$-dimensional manifolds represented as connected sums of Lens spaces, $S^2 \times S^1$, and torus bundles over the circle by certain Morse-Bott functions
本文用特定 Morse-Bott 函数刻画表示为 Lens 空间、$S^2 \ imes S^1$ 和环面在圆上的丛的连通和的 $3$ 维流形，强化并明确了 Saeki 2006 年的相关结果。
In 1967, Chillingworth proved that all convex simplicial 3-balls are collapsible. Using the classical notion of tightness, we generalize this to arbitrary manifolds: We show that all tight simplicial 3-manifolds admit some perfect discrete Morse function. We also strengthen Chillingworth's theorem by proving that all convex simplicial 3-balls are non-evasive. In contrast, we show that many non-evasive 3-balls are not convex.
On Uniformly Perfect Morse Boundaries
本文研究了proper geodesic metric spaces中均匀完美Morse边界的概念，并证明了非平凡群的Morse边界在非空时的均匀完美性，同时建立了相关边界的同胚刚性定理。
We study the coarse geometry of the moduli space of dilation tori with two singularities and the dynamical properties of the action of the Teichmuller flow on this moduli space. This leads to a proof that the vertical foliation of a dilation torus is almost always Morse-Smale. As a corollary, we get that the generic piecewise affine circle homeomorphism with two break points -with respect to the Lebesgue measure- is Morse-Smale.
Uniform Perfectness and Centers in Sublinearly Morse Boundaries
研究次线性Morse边界中均匀完美性何时检测中心穷竭性，通过局部有限树和一般测地空间给出等价条件与度量变换刻画。
Let $M$ be a compact surface and $P$ be a one dimensional manifold without boundary, that is the line $\mathbb{R}^1$ or a circle $S^1$. The classification of path-components of the space of Morse maps from $M$ into $P$ was recently obtained by S. V. Matveev and V. V. Sharko for the case $P=\mathbb{R}$. For $P=S^1$ the classification was obtained by the author. All this results can be reformulated as one theorem: "Two Morse maps $f,g:M \to P$ belong to the same path component of a space of Morse mappings from $M$ into $P$ if and only if they are homotopic and have the same number of crutucal po…
Let E be a circle bundle over a Riemann surface that supports a contact structure transverse to the fibers. This paper presents a combinatorial definition of a differential graded algebra (DGA) that is an invariant of Legendrian knots in E. The invariant generalizes Chekanov's combinatorial DGA invariant of Legendrian knots in the standard contact 3-space using ideas from Eliashberg, Givental, and Hofer's contact homology. The main difficulty lies in dealing with what are ostensibly 1-parameter families of generators for the DGA; these are solved using ``Morse-Bott'' techniques. As an applicat…
The works of Donaldson and Mark make the structure of the Seiberg-Witten invariant of 3-manifolds clear. It corresponds to certain torsion type invariants counting flow lines and closed orbits of a gradient flow of a circle-valued Morse map on a 3-manifold. We study these invariants using the Morse-Novikov theory and Heegaard splitting for sutured manifolds, and make detailed computations for knot complements.
Normal forms of functions with degenerate singularities on surfaces equipped with semi-free circle actions
本文研究了特定曲面上无鞍点Morse-Bott函数的推广类，证明了此类光滑圆周值函数可表示为由最简单Morse函数、微分同胚及光滑函数复合而成的规范型。
Given a circle-valued Morse function of a closed oriented manifold, we prove 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 paper gives a generalization of the result of Hutchings and Lee on abelian coefficients to the case of skew fields. As a consequence we obtain a Morse theoretical and dynamical description of the higher-order Reidemeister torsion.
Morse-Novikov theory for links
研究S^3中链环补的Thurston多面体的纤维面，利用非交换Novikov同调证明二桥链环的纤维化判据，并计算多数低交叉数素链环的Morse-Novikov数。
Let $ω$ be a Morse form on a manifold $M$. Let $p:\hat M\to M$ be a regular covering with structure group $G$, such that $p^*([ω])=0$. Let $ξ:G\to\mathbf{R}$ be the corresponding period homomorphism. Denote by ${\hat Λ}_ξ$ the Novikov completion of the group ring $\mathbf{Z} G$. Choose a transverse $ω$-gradient $v$. Counting the flow lines of $v$ one defines the Novikov complex $\mathcal{N}_*$ freely generated over ${\hat Λ}_ξ$ by the set of zeroes of $ω$. In this paper we introduce a refinement of this construction. We define a subring $\hatΛ_Γ$ of ${\hat Λ}_ξ$ and show that the Novikov compl…
Homotopy type of stabilizers of circle-valued functions with non-isolated singularities on surfaces
本文研究了有向曲面上光滑函数稳定子的同伦性质，完整描述了一类Morse-Bott函数推广的光滑函数稳定子恒等映射连通分量的同伦类型。
Homotopy types of diffeomorphisms groups of simplest Morse-Bott foliations on lens spaces, 2
本文证明透镜空间上最简单 Morse-Bott 叶状结构的保叶微分同胚群到不交换奇异圆的叶状微分同胚群的包含映射是同伦等价。
Virtual Morse-Bott index, moduli spaces of pairs, and applications to topology of smooth four-manifolds
本文研究了圈作用下哈密顿函数的虚拟Morse-Bott指数，证明其与经典Morse-Bott指数一致，并利用Hirzebruch-Riemann-Roch定理计算了所有临界层的虚拟指数，验证了四维光滑流形的Bogomolov-Miyaoka-Yau不等式猜想。
We obtain rigidity and gluing results for the Morse complex of a real-valued Morse function as well as for the Novikov complex of a circle-valued Morse function. A rigidity result is also proved for the Floer complex of a hamiltonian defined on a closed symplectic manifold $(M,ω)$ with $c_{1}|_{π_{2}(M)}=[ω]|_{π_{2}(M)}=0$. The rigidity results for these complexes show that the complex of a fixed generic function/hamiltonian is a retract of the Morse (respectively Novikov or Floer) complex of any other sufficiently $C^{0}$ close generic function/hamiltonian. The gluing result is a type of Maye…
In various situations in Floer theory, one extracts homological invariants from "Morse-Bott" data in which the "critical set" is a union of manifolds, and the moduli spaces of "flow lines" have evaluation maps taking values in the critical set. This requires a mix of analytic arguments (establishing properties of the moduli spaces and evaluation maps) and formal arguments (defining or computing invariants from the analytic data). The goal of this paper is to isolate the formal arguments, in the case when the critical set is a union of circles. Namely, we state axioms for moduli spaces and eval…
Extremal Area of Polygons, sliding along a Circle
本文研究了顶点在圆或椭圆上的多边形面积函数的临界构型，计算了孤立临界点的莫尔斯指数，并将退化点与特征值问题关联，揭示了偶数维中的非孤立奇点结构。
Let $f$ be a real- or circle-valued Morse function on a compact surface M having exactly $n>0$ critical points. Denote by $O$ the orbit of $f$ with respect to the right action of the group of diffeomorphisms of $M$. We show that the connected components of $O$ have the homotopy type of a finite-dimensional CW-complex. Actually, these connected components are homotopy equivalent to a certain covering space of the $n$-th configuration space of the interior of $M$. As a consequence we obtain that the fundamental group of $O$ is a subgroup of the $n$-th braid group of $M$.
This paper was motivated by work of Arnold where he explains how to count "snakes", i.e. Morse functions on the real axis with prescribed behavior at infinity. This leads immediately to a count of excellent Morse functions on the circle, where following Thom's terminology, excellent means that no two critical points lie on the same level set. We explain how to count equivalence classes of excellent Morse functions on the 2-sphere. We consider two equivalence relations. The geometric relation (two functions are equivalent if one can be obtained from the other via compositions with an orientatio…
The oriented area function $A$ is (generically) a Morse function on the space of planar configurations of a polygonal linkage. We are lucky to have an easy description of its critical points as cyclic polygons and a simple formula for the Morse index of a critical point. However, for planar polygons, the function $A$ in many cases is not a perfect Morse function. In particular, for an equilateral pentagonal linkage it has one extra local maximum (except for the global maximum) and one extra local minimum. In the present paper we consider the space of 3D configurations of a polygonal linkage. F…
We make a detailed study of various (quadratic and linear) Morse-Bott trace functions on the orthogonal groups $O(n)$. We describe the critical loci of the quadratic trace function Tr$(AXBX^T)$ and determine their indices via perfect fillings of tables associated with the multiplicities of the eigenvalues of $A$ and $B$. We give a simplified treatment of T. Frankel's analysis of the linear trace function on $SO(n)$, as well as a combinatorial explanation of the relationship between the mod $2$ Betti numbers of $SO(n)$ and those of the Grassmannians $\mathbb{G}(2k,n)$ obtained from this analysi…
Almost Hermitian structures on moduli spaces of non-Abelian monopoles and applications to the topology of symplectic four-manifolds
本文通过Morse理论研究非阿贝尔单极模空间的几乎正交结构，证明了辛四维流形上Bogomolov-Miyaoka-Yau不等式成立。
Morse functions with regular level sets consisting of $2$-dimensional spheres, $2$-dimensional tori, or Klein Bottles
研究3维闭 manifold 上由球面、环面或克莱因瓶构成的正则水平集的莫尔斯函数，扩展了Saeki 2006年的可定向情况，并分类了具有给定正则水平集的莫尔斯函数。
Homotopy types of diffeomorphism groups of polar Morse-Bott foliations on lens spaces, 1
本文研究实心环体及粘合所得透镜空间上的极 Morse-Bott 叶状结构，证明边界固定且保叶微分同胚群可缩，并计算透镜空间上相应保叶微分同胚群的同伦型。
Reeb graph invariants of Morse functions and $3$-manifold groups
本文研究闭流形上具有非平凡 Reeb 图的 Morse 函数，针对 $3$-流形给出最少临界点刻画，并引入流形群新不变量，借助 Heegaard 分裂与 Freiheitssatz 判定无序 Morse 函数。
Diffeomorphism groups of Morse-Bott foliation on the solid Klein bottle by Klein bottles parallel to the boundary
本文研究实心 Klein 瓶及其扭曲丛上的 Morse–Bott Klein 瓶叶状结构，并确定相关叶状保持与逐叶保持微分同胚群的同伦型。
Depth-one foliations, pseudo-Anosov flows and universal circles
本文证明在闭无环面三维流形中，拉紧深度一叶状结构相关的万有圆同构于无完美拟合伪Anosov流的理想边界，并推论该横截伪Anosov流在轨道等价下至多唯一。
Quasisections of circle bundles and Euler class
本文研究定向闭曲面上圆丛的拟截面，推导出用拟截面奇点权之和表示欧拉数的局部公式，并证明其唯一性，建立了与 Kazarian 关于 Morse 分岔公式的联系。
The diameter function is a topological Morse function
本文证明了Teichmüller空间上的直径函数是拓扑Morse函数，作为映射类群等变拓扑Morse函数，其临界点与模空间的同调相关。
Let $M$ be a smooth compact surface, orientable or not, with boundary or without it, $P$ either the real line $R^1$ or the circle $S^1$, and $Diff(M)$ the group of diffeomorphisms of $M$ acting on $C^{\infty}(M,P)$ by the rule $h\cdot f\mapsto f \circ h^{-1}$, where $h\in Diff(M)$ and $f \in C^{\infty}(M,P)$. Let $f:M \to P$ be a Morse function and $O(f)$ be the orbit of $f$ under this action. We prove that $π_k O(f)=π_k M$ for $k\geq 3$, and $π_2 O(f)=0$ except for few cases. In particular, $O(f)$ is aspherical, provided so is $M$. Moreover, $π_1 O(f)$ is an extension of a finitely generated …
Boundedness of bundle diffeomorphism groups over a circle
本文研究圆周上丛微分同胚群的有界性，通过构造拟同态、引入整数k，刻画了群的一致完满性与有界性的判定条件，并结合映射环面粘贴映射给出具体实例。
Let M be a smooth connected compact surface, P be either the real line R^1 or the circle S^1, and f:M-->P be a smooth mapping. In a previous series of papers for the case when f is a Morse map the author calculated the homotopy types of stabilizers and orbits of f with respect to the right action of the diffeomorphisms group of M. The present paper extends those calculations to a large class of maps M-->P with degenerate singularities satisfying certain set of axioms.
Let $M$ be a connected compact orientable surface, $f:M\to \mathbb{R}$ be a Morse function, and $h:M\to M$ be a diffeomorphism which preserves $f$ in the sense that $f\circ h = f$. We will show that if $h$ leaves invariant each regular component of each level set of $f$ and reverses its orientation, then $h^2$ is isotopic to the identity map of $M$ via $f$-preserving isotopy. This statement can be regarded as a foliated and a homotopy analogue of a well known observation that every reversing orientation orthogonal isomorphism of a plane has order $2$, i.e. is a mirror symmetry with respect to …
Let M be a smooth connected compact surface, P be either the real line R^1 or the circle S^1. For a subset X of M denote by D(M,X) the group of diffeomorphisms of M fixed on X. In this note we consider a special class F of smooth maps f:M\to P with isolated singularities which includes all Morse maps. For each such map f from F we consider certain submanifolds X of M that are "adopted" with f in a natural sense, and study the right action of the group D(M,X) on C^{\infty}(M,P). The main result describes the homotopy types of the connected components of the stabilizers S(f) and orbits O(f) for …
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