Forward-modulated damping estimates and nonlocalized stability of periodic Lugiato–Lefever waves

In an interesting recent analysis, Haragus-Johnson-Perkins-de Rijk have shown modulational stability under localized perturbations of steady periodic solutions of the Lugiato-Lefever equation (LLE), in the process pointing out a difficulty in obtaining standard"nonlinear damping estimates"on modulated perturbation variables to control regularity of solutions. Here, we point out that in place of standard"inverse-modulated"damping estimates, one can alternatively carry out a damping estimate on the"forward-modulated"perturbation, noting that norms of forward- and inverse-modulated variables are equivalent modulo absorbable errors, thus recovering the classical argument structure of Johnson-Noble-Rodrigues-Zumbrun for parabolic systems. This observation seems of general use in situations of delicate regularity. Applied in the context of (LLE) it gives the stronger result of stability and asymptotic behavior with respect to nonlocalized perturbations.