Stability of periodic waves in the model with intensity--dependent dispersion

TL;DR

This paper analyzes the stability of standing periodic waves in a nonlinear Schrödinger model with intensity-dependent dispersion, identifying conditions for stability and instability as wave profiles transition from smooth to peaked.

Contribution

It establishes the existence of two families of periodic waves separated by a homoclinic orbit and derives a sharp stability criterion based on the period function.

Findings

Both wave families are stable at small frequencies.

Waves become unstable as frequency approaches the peaked wave limit.

The period function's monotonicity determines stability regions.

Abstract

We study standing periodic waves modeled by the nonlinear Schrodinger equation with the intensity-dependent dispersion coefficient. Spatial periodic profiles are smooth if the frequency of the standing waves is below the limiting frequency, for which the profiles become peaked (piecewise continuously differentiable with a finite jump of the first derivative). We prove that there exist two families of the periodic waves with smooth profiles separated by a homoclinic orbit and the period function (the energy-to-period mapping) is monotonically increasing for the family inside the homoclinic orbit and decreasing for the family outside the homoclinic orbit. This property allows us to derive a sharp criterion for the energetic stability of such standing periodic waves under time evolution if the perturbations are periodic with the same period for both families and, additionally, for the family outside the homoclinic orbit, spatially odd with respect to the half-period. By numerically approximating the sharp stability criterion, we show that both families are energetically stable for small frequencies but become unstable when the frequency approaches the limiting frequency of the peaked waves.