Sideband instability
= Sideband instability
A sideband instability is growth of disturbances with <wavenumbers> slightly displaced from a carrier pattern's <wavenumber>. A real physical perturbation uses the displaced mode together with its <complex conjugate>; a <complex amplitude> equation can couple those two sidebands through its cubic term. The <Eckhaus instability> is a longitudinal phase-modulation example.