Abstract

In this paper we obtain the following stability result for periodic multi-solitons of the KdV equation: We prove that under any given semilinear Hamiltonian perturbation of small size varepsilon > 0, a large class of periodic multi-solitons of the KdV equation, including ones of large amplitude, are orbitally stable for a time interval of length at least O(varepsilon ^{-2}). To the best of our knowledge, this is the first stability result of such type for periodic multi-solitons of large size of an integrable PDE.

Highlights

  • The Korteweg-de Vries (KdV) equation∂t u = −∂x3u + 6u∂x u (1.1)is one of the most important model equations for describing dispersive phenomena

  • In this paper we obtain the following stability result for periodic multisolitons of the KdV equation: We prove that under any given semilinear Hamiltonian perturbation of small size ε > 0, a large class of periodic multi-solitons of the KdV equation, including ones of large amplitude, are orbitally stable for a time interval of length at least O(ε−2)

  • The aim of this paper is to study in the periodic setup the long time asymptotics of the solutions of Hamiltonian perturbations of (1.1) with initial data close to a periodic multisoliton of arbitrary large amplitude

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Summary

Introduction

Is one of the most important model equations for describing dispersive phenomena. It is named after the two Dutch mathematician Korteweg and de Vries [29] (cf. Boussinesq [14], Raleigh [40]) and originally was proposed as a model equation in one space dimension for long surface waves of water in a narrow and shallow channel. This means that we normalize the terms in the Taylor expansion of the Hamiltonian vector field XH which do not contain w and are homogeneous of order at most two This is achieved by a standard normal form procedure which consists in constructing a canonical transformation, given by the time one flow map F of a Hamiltonian vector field XF with a Hamiltonian F of the form. For Hamiltonian perturbations of linear integrable PDEs on T1, which satisfy nonresonance conditions, a standard normal form method has been developed allowing to prove the stability of the equilibrium solution u ≡ 0 of (Hamiltonian) perturbations for time intervals of large size—see e.g. A key ingredient are the normal form coordinates, constructed in [27]

Para-Differential Calculus
Para-Differential Vector Fields
Smoothing Normal Form Steps
Normalization Steps by Para-Differential Calculus
Measure Estimates
Standard Results on Homological Equations
On a Class of Linear Para-Differential Equations
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