Exponentially and non-exponentially small splitting of separatrices for the pendulum with a fast meromorphic perturbation

TL;DR

This paper investigates how the size of separatrix splitting in a pendulum system with fast meromorphic perturbations varies with the analyticity strip width, revealing exponential and non-exponential smallness regimes.

Contribution

It introduces new results on the sensitivity of separatrix splitting to the analyticity strip width in systems with meromorphic perturbations, extending beyond previous algebraic or trigonometric assumptions.

Findings

Splitting is exponentially small with wide analyticity strips.

Splitting increases as the strip narrows, becoming non-exponentially small.

Polynomial truncations are inadequate for accurate splitting estimates.

Abstract

In this paper we study the splitting of separatrices phenomenon which arises when one considers a Hamiltonian System of one degree of freedom with a fast periodic or quasiperiodic and meromorphic in the state variables perturbation. The obtained results are different from the previous ones in the literature, which mainly assume algebraic or trigonometric polynomial dependence on the state variables. As a model, we consider the pendulum equation with several meromorphic perturbations and we show the sensitivity of the size of the splitting on the width of the analyticity strip of the perturbation with respect to the state variables. We show that the size of the splitting is exponentially small if the strip of analyticity is wide enough. Furthermore, we see that the splitting grows as the width of the analyticity strip shrinks, even becoming non-exponentially small for very narrow strips. Our results prevent from using polynomial truncations of the meromorphic perturbation to compute the size of the splitting of separatrices.