Todor Mitev, Georgi Popov
A Gevrey symplectic normal form of an analytic and more generally Gevrey smooth Hamiltonian near a Lagrangian invariant torus with a Diophantine vector of rotation is obtained. The normal form implies effective stability of the quasi-periodic motion near the torus.
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We consider Gevrey perturbations $H$ of a completely integrable Gevrey Hamiltonian $H_0$. Given a Cantor set $Ω_κ$ defined by a Diophantine condition, we find a family of KAM invariant tori of $H$ with frequencies $ω\in Ω_κ$ which is Gevrey smooth in a Whitney sense. Moreover, we obtain a symplectic Gevrey normal form of the Hamiltonian in a neighborhood of the union $Λ$ of the invariant tori. This leads to effective stability of the quasiperiodic motion near $Λ$.
In this short note, we prove that a quasi-periodic torus, with a non-resonant frequency (that can be Diophantine or Liouville) and which is invariant by a sufficiently regular Hamiltonian flow, is KAM stable provided it is Kolmogorov non-degenerate. When the Hamiltonian is smooth (respectively Gevrey-smooth, respectively real-analytic), the in-variant tori are smooth (respectively Gevrey-smooth, respectively real-analytic). This answers a question raised in a recent work by Eliasson, Fayad and Krikorian ([EFK]). We also take the opportunity to ask other questions concerning the stability of no…
We consider standard-like/Froeschlé maps with a dissipation and nonlinear perturbation. That is \[ T_\varepsilon(p,q) = \left( (1 - γ\varepsilon^3) p + μ+ \varepsilon V'(q), q + (1 - γ\varepsilon^3) p + μ+ \varepsilon V'(q) \mod 2 π\right) \] where $p \in \mathbb{R}^D$, $q \in 2 π\mathbb{T}^D$ are the dynamical variables. The $μ\in \mathbb{R}^D, γ\in \mathbb{R}$ are parameters of the model. We assume that the potential $V$ is a trigonometric polynomial. Note that when $γ\ne 0$, the perturbation parameter $\varepsilon$ creates dissipation, which has a drastic effect on the existence of quasi-pe…
When a Gevrey smooth perturbation is applied to a quasi-convex integrable Hamiltonian, it is known that the KAM invariant tori that survive are sticky, that is, doubly exponentially stable. We show by examples the optimality of this effective stability.
In this paper, we give a new construction of resonant normal forms with a small remainder for near-integrable Hamiltonians at a quasi-periodic frequency. The construction is based on the special case of a periodic frequency, a Diophantine result concerning the approximation of a vector by independent periodic vectors and a technique of composition of periodic averaging. It enables us to deal with non-analytic Hamiltonians, and in this first part we will focus on Gevrey Hamiltonians and derive normal forms with an exponentially small remainder. This extends a result which was known for analytic…
We consider a singular perturbation for a family of analytic symplectic maps of the annulus possessing a KAM torus. The perturbation introduces dissipation and contains an adjustable parameter. By choosing the adjustable parameter, one can ensure that the torus persists under perturbation. Such models are common in celestial mechanics. In field theory, the adjustable parameter is called the counterterm and in celestial mechanics, the drift. It is known that there are formal expansions in powers of the perturbation both for the quasi-periodic solution and the counterterm. We prove that the asym…
For an integrable Tonelli Hamiltonian with $d\ (d\geq 2)$ degrees of freedom, we show that all of the Lagrangian tori can be destroyed by analytic perturbations which are arbitrarily small in the $C^{d-δ}$ topology.
Long time stability for Lagrangian tori in infinite dimensional lattice systems
研究无限多个相互弱作用转子的力学系统，通过特定方法证明文献[CGP]中的无限维不变环面是拉格朗日的且长时间稳定。
This paper is a sequel to "Normal forms, stability and splitting of invariant manifolds I. Gevrey Hamiltonians", in which we gave a new construction of resonant normal forms with an exponentially small remainder for near-integrable Gevrey Hamiltonians at a quasi-periodic frequency, using a method of periodic approximations. In this second part we focus on finitely differentiable Hamiltonians, and we derive normal forms with a polynomially small remainder. As applications, we obtain a polynomially large upper bound on the stability time for the evolution of the action variables and a polynomial…
Consider a real--analytic nearly--integrable mechanical system with potential $f$, namely, a Hamiltonian system, having a real-analytic Hamiltonian $$ H(y,x)=\frac12 | y |^2 +\e f(x)\ , $$ $y,x$ being $n$--dimensional standard action--angle variables (and $|\cdot|$ the Euclidean norm). Then, for "general" potentials $f$'s and $\e$ small enough, the Liouville measure of the complementary of invariant tori is smaller than $\e|\ln \e|^a$ (for a suitable $a>0$).
We show that an analytic invariant torus $\cT_0$ with Diophantine frequency $ø_0$ is never isolated due to the following alternative. If the Birkhoff normal form of the Hamiltonian at $\cT_0$ satisfies a Rüssmann transversality condition, the torus $\cT_0$ is accumulated by KAM tori of positive total measure. If the Birkhoff normal form is degenerate, there exists a subvariety of dimension at least $d+1$ that is foliated by analytic invariant tori with frequency $ø_0$. For frequency vectors $ø_0$ having a finite uniform Diophantine exponent (this includes a residual set of Liouville vectors), …
In this paper we study families of Lagrangian tori that appear in a neighborhood of a resonance of a near-integrable Hamiltonian system. Such families disappear in the "integrable" limit $\varepsilon\to 0$. Dynamics on these tori is oscillatory in the direction of the resonance phases and rotating with respect to the other (non-resonant) phases. We also show that, if multiplicity of the resonance equals one, generically these tori occupy a set of large relative measure in the resonant domains in the sense that the relative measure of the remaining "chaotic" set is of order $\sqrt\varepsilon$. …
We study the dynamics of a symplectic twist map without conjugate points. We show that in a neighborhood of a totally periodic Lagrangian manifold, there exists a large family of invariant Lagrangian tori on which the twist map is conjugated to a translation of non-resonant vector.
In 2004, Féjoz [Démonstration du 'théoréme d'Arnold' sur la stabilité du système planétaire (d'après M. Herman). Ergod. Th. & Dynam. Sys. 24(5) (2004), 1521-1582], completing investigations of Herman's [Démonstration d'un théoréme de V.I. Arnold. Séminaire de Systémes Dynamiques et manuscripts, 1998], gave a complete proof of 'Arnold's Theorem' [V. I. Arnol'd. Small denominators and problems of stability of motion in classical and celestial mechanics. Uspekhi Mat. Nauk. 18(6(114)) (1963), 91-192] on the planetary many-body problem, establishing, in particular, the existence of a positive measu…
Asymptotically full measure sets of almost-periodic solutions for the NLS equation
该研究构造了圆周上NLS方程渐近满测度的小振幅几乎周期解，证明极大不变环面为Banach流形，并建立了椭圆不动点的Lyapunov统计稳定性，将经典KAM定理推广至无穷维。
Constructive QP-Time-dependent KAM Algorithm for Lagrangian Tori
本文提出一种计算准周期哈密顿系统中纤维式拉格朗日环面的构造性QP时间依赖KAM算法，其收敛性已获证明，并通过Tokamak模型和涡度缺陷模型展示了应用。
Lagrangian split tori in $S^2 \times S^2$ and billiards
本文证明 $S^2 \times S^2$ 中分裂拉格朗日环面的哈密顿同痕分类等价于矩形台球问题，并据此解决拉格朗日填充数、环面空间拓扑及辛球嵌入像等问题。
In this paper, we show the existence of non contractible periodic orbits in Hamiltonian systems defined on $T^*\T^n$ separating two Lagrangian tori under certain cone assumption. Our result answers a question of Polterovich in \cite{P} in a sharp way. As an application, we find periodic orbits of almost all the homotopy types on a dense set of energy level in Lorentzian type mechanical Hamiltonian systems defined on $T^*\T^2$. This solves a problem of Arnold in \cite{A}.
Pre-Lagrangian tori transverse to an Anosov flow
针对Anosov流横截嵌入环面是否在$\mathbb{R} \times M$中产生拉格朗日量的问题，研究发现存在拓扑障碍导致答案通常否定，仅当诱导叶状结构无平行紧叶时答案为肯定。
More counterexamples to Lagrangian Poincaré recurrence in dimension four
本文扩展了拉格朗日庞加莱回归的反例族，使其覆盖所有非单调环面辛四流形，补充了作者早前关于环面辛四流形反例的研究。
Given a smooth compact Riemannian manifold $M$ and a Hamiltonian $H$ on the cotangent space $T^*M$, strictly convex and superlinear in the momentum variables, we prove uniqueness of certain ergodic invariant Lagrangian graphs within a given homology or cohomology class. In particular, in the context of quasi-integrable Hamiltonian systems, our result implies global uniqueness of Lagrangian KAM tori with rotation vector $ρ$. This result extends generically to the $C^0$-closure of KAM tori.
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