Orbital instability of periodic waves for generalized Korteweg-de Vries-Burgers equations with a source

TL;DR

This paper investigates the orbital instability of periodic waves in generalized Korteweg-de Vries-Burgers equations with a source, establishing conditions under which spectrally unstable waves are also nonlinearly orbitally unstable.

Contribution

It provides a new instability criterion linking spectral and orbital instability for periodic waves in these equations, with applications to specific wave families.

Findings

Spectrally unstable waves are orbitally unstable in the considered equations.

Established local well-posedness and regularity of the Cauchy problem.

Demonstrated orbital instability for small-amplitude waves near a Hopf bifurcation.

Abstract

A family of generalized Korteweg-de Vries-Burgers equations in one space dimension with a nonlinear source is considered. The purpose of this contribution is twofold. On one hand, the local well-posedness of the Cauchy problem on periodic Sobolev spaces and the regularity of the data-solution map are established. On the other hand, it is proved that periodic traveling waves which are spectrally unstable are also orbitally (nonlinearly) unstable under the flow of the evolution equation in periodic Sobolev spaces with same period as the fundamental period of the wave. This orbital instability criterion hinges on the well-posedness of the Cauchy problem, on the smoothness of the data-solution map, as well as on an abstract result which provides sufficient conditions for the instability of equilibria under iterations of a nonlinear map in Banach spaces. Applications of the former criterion include the orbital instability of a family of small-amplitude periodic waves with finite fundamental period for the Korteweg-de Vries-Burgers-Fisher equation, which emerge from a local Hopf bifurcation around a critical value of the velocity.