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Dario Bambusi

Publications and source records attributed to Dario Bambusi.

At least 19 recordsLinked to original sources
arXiv2026

On the integrability of the Kirchhoff-Pohozaev equation on tori

In this paper we study the Kirchhoff-Pohozaev equation introduced in \cite{P2} and its constants of motion (see \cite{BoitiManfrin2025}, \cite{BoitiManfrin2026}) on $n$ dimensional tori. We show that these Hamiltonians are all in involution and we prove that they are generated by an infinite list of constants of motion which are all defined and in involution on a fixed phase space. Then we study the Kirchhoff-Pohozaev equation restricted to a finite Fourier support. In dimension $n=1$ we show that such finite dimensional reduction is always completely integrable and provide an analytic Brikhoff normal form in a neighborhood of the origin. We also give sufficient conditions for integrability for $n>1$. We finally show that the formal Birkhoff Normal form of the Kirchhoff-Pohozaev equation is integrable for $n=1$.

math.DS↗
arXiv2026

Nekhoroshev Theorem for time quasiperiodic perturbations of P-Steep systems

We prove a Nekhoroshev type result for a time quasiperiodic perturbation of an integrable Hamiltonian system. More precisely, we assume that the integrable part is analytic and fulfills a generic nondegeneracy condition introduced by Nekhoroshev and called P-Steepness. We add a small perturbation which depends in a quasiperiodic way on time (with Diophantine frequency) and prove that -- for times exponentially long with the inverse of the size $\varepsilon$ of the perturbation -- the actions of the unperturbed system remain approximately constant. The proof is based on an extension to the time dependent case of the proof {of classical Nekhoroshev's theorem} given by Guzzo, Chierchia and Benettin, which however requires new ideas in order to deal with the more complex geometry of resonances of the time dependent case.

math.DS↗
arXiv2026

A survey on rigorous results for the dynamics of periodic FPU chains

In this paper we review some analytic results on the dynamics of the FPU system. In the first part of the paper, having in mind that the FPU Hamiltonian and the Toda Hamiltonian are close each other, we present some results on the action angle variables of the Toda system and deduce some stability properties for the dynamics of the FPU system. We first focus on the case of finitely many particles and then we study the limit $N\to\infty$. We present also some results on the continous limit of the Toda chain showing that it is well described by a couple of KdV equations. Then we study directly the dynamics of the function interpolating the FPU system and show that the dynamics is Hamiltonian and that the Hamiltonian is very close to a function of the first three Hamiltonians of the KdV hierarchy. In the second part of the paper we present some results valid in the thermodynamic limit, according to which the time autocorrelation functions of some suitably constructed observables decay slowly implying lower bounds on the thermalization times of the system.

math-ph↗
arXiv2025

Non relativistic limit of the nonlinear Klein-Gordon equation: Uniform in time approximation of KAM solutions

We study the non relativistic limit of the solutions of the cubic nonlinear Klein--Gordon (KG) equation with periodic boundary conditions on an interval and we construct a family of time quasi periodic solutions which, after a Gauge transformation, converge globally uniformly in time to quasi periodic solutions of the cubic NLS. The proof is based on KAM theory. We emphasize that, regardless of the spatial domain, all the previous results concern approximations valid over compact time intervals.

math-ph↗
arXiv2025

Almost global existence for Hamiltonian PDEs on compact manifolds

We prove an abstract result of almost global existence of small solutions to semi-linear Hamiltonian partial differential equations satisfying very weak non resonance conditions and basic multilinear estimates. Thanks to works by Delort--Szeftel, these assumptions turn out to typically hold for Hamiltonian PDEs on any smooth compact boundaryless Riemannian manifold. As a main application, we prove the almost global existence of small solutions to nonlinear Klein--Gordon equations on such manifolds: for almost all mass, any arbitrarily large $r$ and sufficiently large $s$, solutions with initial data of sufficiently small size $\varepsilon \ll 1$ in the Sobolev space $H^s \times H^{s-1}$ exist and remain in $H^s \times H^{s-1}$ for polynomial times $|t| \leq \varepsilon^{-r}$. This is the first result of almost global existence without specific assumptions on the compact manifold. We also apply this abstract result to nonlinear Schr{ö}dinger equations close to ground states and nonlinear Klein--Gordon equations on $\mathbb{R}^d$ with positive quadratic potentials.

math.AP↗
arXiv2025

Longtime dynamics for the Landau Hamiltonian with a time dependent magnetic field

We consider a modulated magnetic field, $B(t) = B_0 +\varepsilon f(ωt)$, perpendicular to a fixed plane, where $B_0$ is constant, $\varepsilon>0$ and $f$ a periodic function on the torus ${\mathbb T}^n$. Our aim is to study classical and quantum dynamics for the corresponding Landau Hamiltonian. It turns out that the results depend strongly on the chosen gauge. For the Landau gauge the position observable is unbounded for "almost all" non resonant frequencies $ω$. On the contrary, for the symmetric gauge we obtain that, for "almost all" non resonant frequencies $ω$, the Landau Hamiltonian is reducible to a two dimensional harmonic oscillator and thus gives rise to bounded dynamics. The proofs use KAM algorithms for the classical dynamics. Quantum applications are given. In particular, the Floquet spectrum is absolutely continuous in the Landau gauge while it is discrete, of finite multiplicity, in symmetric gauge.

math.AP↗
arXiv2024

Growth of Sobolev norms in quasi integrable quantum systems

We prove an abstract result giving a $\langle t \rangle^\varepsilon$ upper bound on the growth of the Sobolev norms of a time-dependent Schrödinger equation of the form ${i} \dot ψ= H_0 ψ+ V (t)ψ$. Here $H_0$ is assumed to be the Hamiltonian of a steep quantum integrable system and to be a pseudodifferential operator of order ${\tt d} > 1$; $V (t)$ is a time-dependent family of pseudodifferential operators, unbounded, but of order ${\tt b} < {\tt d}$. The abstract theorem is then applied to perturbations of the quantum anharmonic oscillators in dimension 2 and to perturbations of the Laplacian on a manifold with integrable geodesic flow, and in particular Zoll manifolds, rotation invariant surfaces and Lie groups. The proof is based on a quantum version of the proof of the classical Nekhoroshev theorem.

math.AP↗
arXiv2024

Globally integrable quantum systems and their perturbations

In this paper we present the notion of globally integrable quantum system that we introduced in [BL22]: we motivate it using the spectral theory of pseudodifferential operators and then we give some results on linear and nonlinear perturbations of a globally integrable quantum system. In particular, we give a spectral result ensuring stability of most of its eigenvalues under relatively bounded perturbations, and two results controlling the growth of Sobolev norms when it is subject either to linear unbounded time dependent perturbations or a small nonlinear Hamiltonian nonlinear perturbation.

math.AP↗
arXiv2024

Almost global existence for some Hamiltonian PDEs on manifolds with globally integrable geodesic flow

In this paper we prove an abstract result of almost global existence for small and smooth solutions of some semilinear PDEs on Riemannian manifolds with globally integrable geodesic flow. Some examples of such manifolds are Lie groups (including flat tori), homogeneous spaces and rotational invariant surfaces. As applications of the abstract result we prove almost global existence for a nonlinear Schrödinger equation with a convolution potential and for a nonlinear beam equation. We also prove $H^s$ stability of the ground state in NLS equation. The proof is based on a normal form procedure.

math.AP↗
arXiv2024

A global Nekhoroshev theorem for particles on the torus with time dependent Hamiltonian

We prove a $C^\infty$ global version of Nekhoroshev theorem for time dependent Hamiltonians in $R^d\times T^d$. Precisely, we prove a result showing that for all times the actions of the unperturbed systems are bounded by a constant times $ \langle t\rangle^ε$. We apply the result to the dynamics of a charged particle in $T^d$ subject to a time dependent electromagnetic field.

math-ph↗
arXiv2023

A Nekhoroshev theorem for some perturbations of the Benjamin-Ono equation with initial data close to finite gap tori

We consider a perturbation of the Benjamin Ono equation with periodic boundary conditions on a segment. We consider the case where the perturbation is Hamiltonian and the corresponding Hamiltonian vector field is analytic as a map form energy space to itself. Let $ε$ be the size of the perturbation. We prove that for initial data close in energy norm to an $N$-gap state of the unperturbed equation all the actions of the Benjamin Ono equation remain $\cO(ε^{\frac{1}{2(N+1)}})$ close to their initial value for times exponentially long with $ε^{-\frac{1}{2(N+1)}}$.

math.AP↗
arXiv2022

Almost global existence for some Hamiltonian PDEs with small Cauchy data on general tori

In this paper we prove a result of almost global existence for some abstract nonlinear PDEs on flat tori and apply it to some concrete equations, namely a nonlinear Schrödinger equation with a convolution potential, a beam equation and a quantum hydrodinamical equation. We also apply it to the stability of plane waves in NLS. The main point is that the abstract result is based on a nonresonance condition much weaker than the usual ones, which rely on the celebrated Bourgain's Lemma which provides a partition of the "resonant sites" of the Laplace operator on irrational tori.

math.AP↗
arXiv2021

Spectral asymptotics of all the eigenvalues of Schrödinger operators on flat tori

We study Schrödinger operators with Floquet boundary conditions on flat tori obtaining a spectral result giving an asymptotic expansion of all the eigenvalues. The expansion is in $λ^{-δ}$ with $δ\in(0,1)$ for most of the eigenvalues $λ$ (stable eigenvalues), while it is a "directional expansion" for the remaining eigenvalues (unstable eigenvalues). The proof is based on a structure theorem which is a variant of the one proved in \cite{PS10,PS12} and on a new iterative quasimode argument.

math-ph↗
arXiv2020

Hamiltonian studies on counter-propagating water waves

We use a Hamiltonian normal form approach to study the dynamics of the water wave problem in the small amplitude long wave regime (KdV regime). If $μ$ is the small parameter corresponding to the inverse of the wave length, we show that the normal form at order $μ^5$ consists of two decoupled equation, one describing right going waves and the other describing left going waves. Performing a further non Hamiltonian transformation we conjugate each of these equations to a linear combination of the first three equations in the KdV hierarchy. At order $μ^7$ we find nontrivial terms coupling the two counter-propagating waves.

math-ph↗
arXiv2020

A simple proof for a $C^\infty$ Nekhoroshev theorem

We prove a $C^\infty$ version of the Nekhoroshev's estimate on the stability times of the actions in close to integrable Hamiltonian systems. The proof we give is a variant of the original Nekhoroshev's proof and it consists in first conjugating, globally in the phase space, and up to a small remainder, the system to a normal form. Then we perform the geometric part of the proof in the normalized variables. As a result, we obtain a proof which is simpler than the usual ones.

math.DS↗
arXiv2019

Dispersive estimate for quasi-periodic Schrödinger operators on 1-$d$ lattices

Consider the one-dimensional discrete Schrödinger operator $H_θ$: $$(H_θ q)_n=-(q_{n+1}+q_{n-1})+ V(θ+nω) q_n \ , \quad n\in Z \ ,$$ with $ω\in R^d$ Diophantine, and $V$ a real-analytic function on $ T^d=( R/2πZ)^d$. For $V$ sufficiently small, we prove the dispersive estimate: {for every $ϕ\in\ell^1( Z)$,} $$ \| e^{-{\rm i}tH_θ}ϕ\|_{\ell^\infty} \leq K_0 \frac{ |\ln\varepsilon_0|^{a(\ln\ln(2+\langle t\rangle))^2 d}} {\langle t\rangle^{\frac13}} \|ϕ\|_{\ell^1} \ , \quad \langle t \rangle:=\sqrt{1+t^2} \ ,$$ {with $a$ and $K_0$ two absolute constants} and $\varepsilon_0$ an analytic norm of $V$. The estimate holds for every $θ\in T^d$.

math-ph↗
arXiv2019

Exponential stability in the perturbed central force problem

We consider the spatial central force problem with a real analytic potential. We prove that for all analytic potentials, but the Keplerian and the Harmonic ones, the Hamiltonian fulfills a nondegeneracy property needed for the applicability of Nekhoroshev's theorem. We deduce stability of the actions over exponentially long times when the system is subject to arbitrary analytic perturbation. The case where the central system is put in interaction with a slow system is also studied and stability over exponentially long time is proved.

math-ph↗