arXiv subjects

Elena A. Kudryavtseva

Publications and source records attributed to Elena A. Kudryavtseva.

14 recordsLinked to original sources

arXiv2025

Symplectic classification for universal unfoldings of $A_n$ singularities in integrable systems

In the present paper, we obtain real-analytic symplectic normal forms for integrable Hamiltonian systems with $n$ degrees of freedom near singular points having the type ``universal unfolding of $A_n$ singularity'', $n\ge1$ (local singularities), as well as near compact orbits containing such singular points (semi-local singularities). We also obtain a classification, up to real-analytic symplectic equivalence, of real-analytic Lagrangian foliations in saturated neighborhoods of such singular orbits (semi-global classification). These singularities (local, semi-local and semi-global ones) are structurally stable. It turns out that all integrable systems are symplectically equivalent near their singular points of this type (thus, there are no local symplectic invariants). A complete semi-local (respectively, semi-global) symplectic invariant of the singularity is given by a tuple of $n-1$ (respectively $n-1+\ell$) real-analytic function germs in $n$ variables, where $\ell$ is the number of connected components of the complement of the singular orbit in the fiber. The case $n=1$ corresponds to non-degenerate singularities (of elliptic and hyperbolic types) of one-degree of freedom Hamiltonians; their symplectic classifications were known. The case $n=2$ corresponds to parabolic points, parabolic orbits and cuspidal tori, and the case $n\ge3$ -- to their higher-dimensional analogs.

math.SG↗

arXiv2025

Bifurcations of magnetic geodesic flows on surfaces of revolution

We study magnetic geodesic flows invariant under rotations on the 2-sphere. The dynamical system is given by a generic pair of functions $(f,Λ)$ in one variable. Topology of the Liouville fibration of the given integrable system near its singular orbits and singular fibers is described. Types of these singularities are computed. Topology of the Liouville fibration on regular 3-dimensional isoenergy manifolds is described by computing the Fomenko--Zieschang invariant. All possible bifurcation diagrams of the momentum maps of such integrable systems are described. It is shown that the bifurcation diagram consists of two curves in the $(h,k)$-plane. One of these curves is a line segment $h=0$, and the other lies in the half-plane $h\ge0$ and can be obtained from the curve $(a:-1:k) = (f:Λ:1)^*$ projectively dual to the curve $(f:Λ:1)$ by the transformation $(a:-1:k)\mapsto(a^2/2,k)=(h,k)$.

math.DS↗

arXiv2021

Hidden toric symmetry and structural stability of singularities in integrable systems

The goal of the paper is to develop a systematic approach to the study of (perhaps degenerate) singularities of integrable systems and their structural stability. As the main tool, we use "hidden" system-preserving torus actions near singular orbits. We give sufficient conditions for the existence of such actions and show that they are persistent under integrable perturbations. We find toric symmetries for several infinite series of singularities and prove, as an application, structural stability of Kalashnikov's parabolic orbits with resonances in the real-analytic case. We also classify all Hamiltonian $k$-torus actions near a singular orbit on a symplectic manifold $M^{2n}$ (or on its complexification) and prove that the normal forms of these actions are persistent under small perturbations. As a by-product, we prove an equivariant version of the Vey theorem (1978) about local symplectic normal form of nondegenerate singularities.

math.SG↗

arXiv2021

Topology of spaces of smooth functions and gradient-like flows with prescribed singularities on surfaces

By a gradient-like flow on a closed orientable surface $M$, we mean a closed 1-form $β$ defined on $M$ punctured at a finite set of points (sources and sinks of $β$) such that there exists a Morse function $f$ on $M$, called an energy function of $β$, whose critical points coincide with equilibria of $β$, and the pair $(f,β)$ has a canonical form near each critical point of $f$. Let $\mathcal{B}=\mathcal{B}(β_0)$ be the space of all gradient-like flows on $M$ having the same types of local singularities as a flow $β_0$, and $\mathcal{F}=\mathcal{F}(f_0)$ the space of all Morse functions on $M$ having the same types of local singularities as an energy function $f_0$ of $β_0$. We prove that the spaces $\mathcal{F}$ and $\mathcal{B}$, equipped with $C^\infty$ topologies, are homotopy equivalent to some manifold $\mathcal{M}_s$, moreover their decompositions into $\mathrm{Diff}^0(M)$-orbits are given by two transversal fibrations on $\mathcal{M}_s$. Similar results are proved for topological equivalence classes on $\mathcal{F}$ and $\mathcal{B}$, and for non-Morse singularities.

math.GT↗

arXiv2020

Relatively-periodic solutions of planetary systems with satellites and systems with slow and fast variables

The partial case of the planar $N+1$ body problem, $N\ge2$, of the type of planetary system with satellites is studied. One of the bodies (the Sun) is assumed to be much heavier than the other bodies ("planets" and "satellites"), moreover the planets are much heavier than the satellites, and the "years" are much longer than the "months". The existence of at least $2^{N-2}$ smooth 2-parameter families of symmetric periodic solutions in a rotating coordinate system is proved, such that the distances between each planet and its satellites are much shorter than the distances between the Sun and the planets. The existence of "gaps" in these families of solutions is proved, corresponding to $k:(k+1)$ resonances of angular frequencies of planets' revolution around the Sun. Generating symmetric periodic solutions are described. Sufficient conditions for some periodic solutions to be orbitally stable in linear approximation are given. The results are extended to a class of Hamiltonian systems with slow and fast variables close to the systems of semidirect product type.

math.DS↗

arXiv2020

Superintegrable Bertrand magnetic geodesic flows

The problem of description of superintegrable systems (i.e., systems with closed trajectories in a certain domain) in the class of rotationally symmetric natural mechanical systems goes back to Bertrand and Darboux. We describe all superintegrable (in a domain of slow motions) systems in the class of rotationally symmetric magnetic geodesic flows. We show that all sufficiently slow motions in a central magnetic field on a two-dimensional manifold of revolution are periodic if and only if the metric has a constant scalar curvature and the magnetic field is homogeneous, i.e. proportional to the area form.

math.DS↗

arXiv2016

Topology of the spaces of functions with prescribed singularities on surfaces

Let $M$ be a smooth connected orientable closed surface and $f_0\in C^\infty(M)$ a function having only critical points of the $A_μ$-types, $μ\in\mathbb N$. Let ${\mathcal F}={\mathcal F}(f_0)$ be the set of functions $f\in C^\infty(M)$ having the same types of local singularities as those of $f_0$. We describe the homotopy type of the space $\mathcal F$, endowed with the $C^\infty$-topology, and its decomposition into orbits of the action of the group of "left-right changings of coordinates".

math.GT↗

arXiv2015

Helicity is the only invariant of incompressible flows whose derivative is continuous in $C^1$-topology

Let $Q$ be a smooth compact orientable 3--manifold with smooth boundary $\partial Q$. Let $\mathcal{B}$ be the set of exact 2--forms $B\inΩ^2(Q)$ such that $j_{\partial Q}^*B=0$, where $j_{\partial Q}:{\partial Q}\to Q$ is the inclusion map. The group $\mathcal{D}=\mathrm{Diff}_0(Q)$ of self-diffeomorphisms of $Q$ isotopic to the identity acts on the set $\mathcal{B}$ by $\mathcal{D}\times\mathcal{B}\to\mathcal{B}$, $(h,B)\mapsto h^*B$. Let $\mathcal{B}^\circ$ be the set of 2--forms $B\in\mathcal{B}$ without zeros. We prove that every $\mathcal{D}$--invariant functional $I:\mathcal{B}^\circ\to\mathbb{R}$ having a regular and continuous derivative with respect to the $C^1$--topology can be locally (and, if $Q=M\times S^1$ with $\partial Q\ne\varnothing$, globally on the set of all 2--forms $B\in\mathcal{B}^\circ$ admitting a cross-section isotopic to $M\times\{*\}$) expressed in terms of the helicity.

math.DS↗

arXiv2012

Generalization of Bertrand's theorem to surfaces of revolution

The generalization of Bertrand's theorem to abstract surfaces of revolution without "equators" is proved. We prove a criterion for the existence on such a surface of exactly two central potentials (up to an additive and a multiplicative constants) all of whose bounded nonsingular orbits are closed and which admit a bounded nonsingular noncircular orbit. A criterion for the existence of a unique such potential is proved. The geometry and classification of the corresponding surfaces are described, with indicating either the pair of gravitational and oscillator) potentials or the unique (oscillator) potential. The absence of the required potentials on any surface which does not meet the above criteria is proved.

math.DS↗

arXiv2012

The Liouville-type theorem for integrable Hamiltonian systems with incomplete flows

For integrable Hamiltonian systems with two degrees of freedom whose Hamiltonian vector fields have incomplete flows, an analogue of the Liouville theorem is established. A canonical Liouville fibration is defined by means of an "exact" 2-parameter family of flat polygons equipped with certain pairing of sides. For the integrable Hamiltonian systems given by the vector field $v=(-\partial f/\partial w, \partial f/\partial z)$ on ${\mathbb C}^2$ where $f=f(z,w)$ is a complex polynomial in 2 variables, geometric properties of Liouville fibrations are described.

math.DG↗

arXiv2011

On intersections of closed curves on surfaces

The problem on the minimal number (with respect to deformation) of intersection points of two closed curves on a surface is solved. Following the Nielsen approach, we define classes of intersection points and essential classes of intersection points, which "are preserved under deformation" and whose total number is called the Nielsen number. If each Nielsen class consists of a unique point and has a non-vanishing index after a suitable deformation of the pair of curves, one says that {\it the Wecken property holds}. We compute the minimal number of intersection points in terms of the Nielsen numbers and the Reidemeister numbers. In particular, we prove that the Wecken property does not hold for some pairs of closed curves. Moreover, all the non-vanishing indices of the Nielsen classes equal $\pm1$, while the non-vanishing Jezierski semi-indices equal 1. Similar questions are studied for the self-intersection problem of a curve on a surface.

math.AT↗

arXiv2011

Integrable Hamiltonian systems with incomplete flows and Newton's polygons

We study the Hamiltonian vector field $v=(-\partial f/\partial w,\partial f/\partial z)$ on $\mathbb C^2$, where $f=f(z,w)$ is a polynomial in two complex variables, which is non-degenerate with respect to its Newton's polygon. We introduce coordinates in four-dimensional neighbourhoods of the "points at infinity", in which the function $f(z,w)$ and the 2-form $dz\wedge dw$ have a canonical form. A compactification of a four-dimensional neighbourhood of the non-singular level set $T_0=f^{-1}(0)$ of $f$ is constructed. The singularity types of the vector field $v|_{T_0}$ at the "points at infinity" in terms of Newton's polygon are determined.

math.DG↗

arXiv2011

Connected components of spaces of Morse functions with fixed critical points

Let $M$ be a smooth closed orientable surface and $F=F_{p,q,r}$ be the space of Morse functions on $M$ having exactly $p$ critical points of local minima, $q\ge1$ saddle critical points, and $r$ critical points of local maxima, moreover all the points are fixed. Let $F_f$ be the connected component of a function $f\in F$ in $F$. By means of the winding number introduced by Reinhart (1960), a surjection $π_0(F)\to{\mathbb Z}^{p+r-1}$ is constructed. In particular, $|π_0(F)|=\infty$, and the Dehn twist about the boundary of any disk containing exactly two critical points, exactly one of which is a saddle point, does not preserve $F_f$. Let $\mathscr D$ be the group of orientation preserving diffeomorphisms of $M$ leaving fixed the critical points, ${\mathscr D}^0$ be the connected component of ${\rm id}_M$ in $\mathscr D$, and ${\mathscr D}_f\subset{\mathscr D}$ the set of diffeomorphisms preserving $F_f$. Let ${\mathscr H}_f$ be the subgroup of ${\mathscr D}_f$ generated by ${\mathscr D}^0$ and all diffeomorphisms $h\in{\mathscr D}$ which preserve some functions $f_1\in F_f$, and let ${\mathscr H}_f^{\rm abs}$ be its subgroup generated ${\mathscr D}^0$ and the Dehn twists about the components of level curves of functions $f_1\in F_f$. We prove that ${\mathscr H}_f^{\rm abs}\subsetneq{\mathscr D}_f$ if $q\ge2$, and construct an epimorphism ${\mathscr D}_f/{\mathscr H}_f^{\rm abs}\to{\mathbb Z}_2^{q-1}$, by means of the winding number. A finite polyhedral complex $K=K_{p,q,r}$ associated to the space $F$ is defined. An epimorphism $μ:π_1(K)\to{\mathscr D}_f/{\mathscr H}_f$ and finite generating sets for the groups ${\mathscr D}_f/{\mathscr D}^0$ and ${\mathscr D}_f/{\mathscr H}_f$ in terms of the 2-skeleton of the complex $K$ are constructed.

math.GT↗

arXiv2011

Special framed Morse functions on surfaces

Let $M$ be a smooth closed orientable surface. Let $F$ be the space of Morse functions on $M$, and $\mathbb{F}^1$ the space of framed Morse functions, both endowed with $C^\infty$-topology. The space $\mathbb{F}^0$ of special framed Morse functions is defined. We prove that the inclusion mapping $\mathbb{F}^0\hookrightarrow\mathbb{F}^1$ is a homotopy equivalence. In the case when at least $χ(M)+1$ critical points of each function of $F$ are labeled, homotopy equivalences $\mathbb{\widetilde K}\sim\widetilde{\cal M}$ and $F\sim\mathbb{F}^0\sim{\mathscr D}^0\times\mathbb{\widetilde K}$ are proved, where $\mathbb{\widetilde K}$ is the complex of framed Morse functions, $\widetilde{\cal M}\approx\mathbb{F}^1/{\mathscr D}^0$ is the universal moduli space of framed Morse functions, ${\mathscr D}^0$ is the group of self-diffeomorphisms of $M$ homotopic to the identity.

math.GT↗