arXiv subjects

Gabriella Pinzari

Publications and source records attributed to Gabriella Pinzari.

At least 19 recordsLinked to original sources

arXiv2026

No infinite spin for total collisions in the spatial N-body problem

In the $n$-body problem, when bodies tend to a total collision, then its normalized shape curve converges to the set of normalized central configurations, which has $SO(3)$ symmetry in the planar case. This leaves a possibility that the normalized shape curve tends to the set obtained by rotations of some central configuration instead of a particular point on it. This is the \emph{infinite spin problem} which concerns the rotational behavior of total collision orbits in the $n$-body problem. We show that the infinite spin is not possible if the limiting shape is isolated from other connected components of the set of normalized central configurations. Our approach extends the method from recent work for total collision for the planar case by Moeckel and Montgomery. The main tool is a full reduction $\rm SO(3)$--symmetry in a context of vanishing angular momentum.

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arXiv2026

Improved stability estimates at elliptic equilibria of Hamiltonian systems

This paper deals with an improvement of the "a-priori stability bounds" on the variation of the action variables and on the stability time obtained from a given Birkhoff normal form around the elliptic equilibrium point of an Hamiltonian system satisfying a non-resonance condition of finite order N. In particular, we improve the standard a-priori lower bound on the stability time from a purely linear dependence on the inverse of the polynomial norm of the remainder of the normal form to the sum of a linear term (which is still present but with a different constant coefficient) and a quadratic one. The prevalence between the linear and the quadratic term depends on the resonance properties of all the monomials in the remainder of the normal form with degree from N to a finite order M. We also provide a comparative example of the new estimates and the traditional a priori ones in the framework of computer-assisted proofs.

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arXiv2025

Projective deduction of the non-trivial first integral to the Euler problem: an explicit computation

The validity of Kepler Laws for the {\it spherical Kepler problem} -- namely, the problem of the motion of a particle on the unit sphere {in $\mathbb R^3$} undergoing an attraction by another particle in the sphere, tangent to the geodesic line between the two and inversely proportional to its squared length -- prompted geometers to try to interpret such system as a '' projection'' of the familiar Kepler problem in the plane, with the hosting plane given by some affine plane in $\mathbb R^3$. At this respect, the most convenient mutual sphere-plane position has been object of a long debate, an account of which can be found in \cite{Albouy2013}. This fascinating topic, resumed %subject, firstly by A. Albouy in the aforementioned paper, has been expanded from the theoretical side in \cite{Albouy2015}. Further investigations recently appeared in \cite{AlbouyZhao2019, Zhao1, TakeuchiZhao1, TakeuchiZhao2}. As remarked in \cite{Albouy2013, Albouy2015}, extensions of the procedure to more dynamical systems would open to the possibility of finding first integrals to a given dynamical system simply looking at the energy of the mirror problem. In this note, we focus on the case of the problem of two fixed centers, already mentioned in \cite{Albouy2013}. We provide a{n explicit} geometrical construction allowing to interpret the first integral of the problem as the energy of its projection on an ellipsoid. Compared to previous papers on the same subject, ours -- besides being based on a somehow different construction -- includes complete explicit computations. {A byproduct of our construction is the existence of two integrable mirror problems (equivalently, three quadratic integrals, including the energy) for the Kepler problem, which is an aspect of its super-integrability.

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arXiv2025

Two Layer Model via Non Quasi Periodic Normal Form Theory

The two layer model is a 2+1/2 degrees of freedom non autonomous dynamical system whose lower order expansion exhibits capture in resonance, numerically detected in a previous paper by the authors. In this paper, we reframe the model along the lines of a suitable version of (which we refer to as non quasi periodic) normal form theory and provide an explicit amount of the resonance trapping time, which is estimated as exponentially long, in terms of the small parameters of the system. Key words: capture into resonance; non quasi periodic normal form theory; friction. MSC 2020: 37J40; 70F40.

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arXiv2025

A common first integral from three-body secular theory and Kepler billiards

We observe that a particular first integral of the partially-averaged system in the secular theory of the three-body problem appears also as an important conserved quantity of integrable Kepler billiards. In this note we illustrate their common roots with the projective dynamics of the two-center problem. We then combine these two aspects to define a class of integrable billiard systems on surfaces of constant curvature.

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arXiv2023

Non Quasi-Periodic Normal Form Theory

We review a recent generalization of Normal Form Theory to systems (Hamiltonian ones or general ODEs) where the perturbing term is not periodic in one coordinate variable. The main difference with the standard case relies on the non uniqueness of the Normal Form and the total absence of the small divisors problem. The exposition is quite general, so as to allow extensions to the case of more non--periodic coordinates, and more functional settings. Here, for simplicity, we work in the real--analytic class.

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arXiv2023

Quantitative KAM theory, with an application to the three-body problem

Based on quantitative ``{\sc kam} theory'', we state and prove two theorems about the continuation of maximal and whiskered quasi--periodic motions to slightly perturbed systems exhibiting proper degeneracy. Next, we apply such results to prove that, in the three--body problem, there is a small set in phase space where it is possible to detect both such families of tori. We also estimate the density of such motions in proper ambient spaces. Up to our knowledge, this is the first proof of co--existence of stable and whiskered tori in a physical system.

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arXiv2022

Perturbation theory and canonical coordinates in celestial mechanics

KAM theory owes most of its success to its initial motivation: the application to problems of celestial mechanics. The masterly application was offered by V.I.Arnold in the 60s who worked out a theorem, that he named the Fundamental Theorem (FT), especially designed for the planetary problem. However, FT could be really used at that purpose only when, about 50 years later, a set of coordinates constructively taking the invariance by rotation and close-to-integrability into account was used. Since then, some progress has been done in the symplectic assessment of the problem, and here we review such results.

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arXiv2022

Proof of a conjecture by H. Dullin and R. Montgomery

In the framework of the planar Euler problem in the quasi--periodic regime, the formulae of the periods available in the literature are simple only on one side of their singularity. In this paper, we complement such formulae with others, which result simpler on the other side. The derivation of such new formulae uses the Keplerian limit and complex analysis tools. As an application, we prove a conjecture by H. Dullin and R. Montgomery, which states that such periods, as well as their ratio, the {\it rotation number}, are monotone functions of their non--trivial first integral, at any fixed energy level.

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arXiv2022

A new analysis of the three--body problem

In the recent papers~[18],~[5], respectively, the existence of motions where the perihelions afford periodic oscillations about certain equilibria and the onset of a topological horseshoe have been proved. Such results have been obtained using, as neighbouring integrable system, the so--called two--centre (or {\it Euler}) problem and a suitable canonical setting proposed in~[16],~[17]. Here we review such results.

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arXiv2022

Lonely planets and light belts: the Statistical Mechanics of Gravitational Systems

In this paper we propose a notion of stability, that we call $ε-N$-stability, for systems of particles interacting via Newton's gravitational potential, and orbiting a much bigger object. For these systems the usual thermodynamical stability condition, ensuring the possibility to perform the thermodynamical limit, fails, but one can use as relevant parameter the maximum number of particles $N$ that guarantees the $ε-N$-stability. With some judicious but not particularly optimized estimates, borrowed from the classical theory of equilibrium statistical mechanics, we show that our model has a good fit with the data observed in the Solar System, and it gives a reasonable interpretation of some of its global properties.

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arXiv2022

Euler integral as a source of chaos in the three-body problem

In this paper we address, from a purely numerical point of view, the question, raised in [20, 21], and partly considered in [22, 9, 3], whether a certain function, referred to as "Euler Integral", is a quasi-integral along the trajectories of the three-body problem. Differently from our previous investigations, here we focus on the region of the "unperturbed separatrix", which turns to be complicated by a collision singularity. Concretely, we reduce the Hamiltonian to two degrees of freedom and, after fixing some energy level, we discuss in detail the resulting three-dimensional phase space around an elliptic and an hyperbolic periodic orbit. After measuring the strength of variation of the Euler Integral (which are in fact small), we detect the existence of chaos closely to the unperturbed separatrix. The latter result is obtained through a careful use of the machinery of covering relations, developed in [13, 24, 23].

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arXiv2021

Exponential stability of fast driven systems, with an application to celestial mechanics

We construct a normal form suited to {\it fast driven systems}. We call so systems including actions ${\rm I}$, angles {$ψ$}, and one fast coordinate $y$, moving under the action of a vector--field $N$ depending only on ${\rm I}$ and $y$ and with vanishing ${\rm I}$--components. {In absence of the coordinate $y$, such systems have been extensively investigated and it is known that, after a small perturbing term is switched on, the normalised actions ${\rm I}$ turn to have exponentially small variations compared to the size of the perturbation. We obtain the same result of the classical situation, with the additional benefit that } no trapping argument is needed, as no small denominator arises. {We use the result to prove that, in the three--body problem, the level sets of a certain function called {\it Euler integral} have exponentially small variations in a short time, closely to collisions.}

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arXiv2020

Symbolic dynamics in a binary asteroid system

We highlight the existence of a topological horseshoe arising from a a--priori stable model of the binary asteroid dynamics. The inspection is numerical and uses correctly aligned windows, as described in a recent paper by A. Gierzkiewicz and P. Zgliczyński, combined with a recent analysis of an associated secular problem.

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arXiv2020

A first integral to the partially averaged Newtonian potential of the three-body problem

We consider the partial average i.e., the Lagrange average with respect to {\it just one} of the two mean anomalies, of the Newtonian part of the perturbing function in the three--body problem Hamiltonian. We prove that such a partial average exhibits a non--trivial first integral. We show that this integral is fully responsible of certain cancellations in the averaged Newtonian potential, including a property noticed by Harrington in the 60s. We also highlight its joint rôle (together with certain symmetries) in the appearance of the so called "Herman resonance". Finally, we discuss an application and an open problem.

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arXiv2020

Euler integral and perihelion librations

We discuss dynamical aspects of an analysis of the two--centre problem started in [15]. The perturbative nature of our approach allows us to foresee applications to the three--body problem.

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arXiv2020

Perihelion librations in the secular three--body problem

A normal form theory for non--quasi--periodic systems is combined with the special properties of the partially averaged Newtonian potential pointed out in [15] to prove, in the averaged, planar three--body problem, the existence of a plenty of motions where, periodically, the perihelion of the inner body affords librations about one equilibrium position and its ellipse squeezes to a segment before reversing its direction and again decreasing its eccentricity (perihelion librations).

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arXiv2018

On the co--existence of maximal and whiskered tori for the planetary three--body problem

In this paper we discuss about the possibility of {\it coexistence} of stable and unstable quasi--periodic {\sc kam} tori in a region of phase space of the three-body problem. The {argument of proof} goes along {{\sc kam} theory and, especially,} the production of two non smoothly related systems of canonical coordinates in the same region of the phase space, the possibility of which is foreseen, for `properly--degenerate' systems, by a theorem of Nekhorossev and Mi{š}{č}enko and Fomenko. The two coordinate systems are alternative to the classical reduction of the nodes by Jacobi, described, e.g., in~[V.I.~Arnold, Small denominators and problems of stability of motion in classical and celestial mechanics, 18, 85 (1963); p. 141].

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