Coupling of Coaxial Roton Spiral Waves

In this section we derive a compact coupling model for self-stable coaxial cylindrical (spiral) LEDO-waves, as they occur in the Roton-Model. We consider two Roton-spiral waves located on different ring radii, and compute how strongly the outer spiral wave can couple inward to the inner spiral wave. We also identify the geometric and frequency conditions for forward coupling, resonance, and the possibility of a backward-running component.