Spectral asymptotics of the Laplacian on Platonic solids graphs

We investigate the high-energy eigenvalue asymptotics of quantum graphs consisting of the vertices and edges of the five Platonic solids considering two different types of the vertex coupling. One is the standard δ-condition and the other is the preferred-orientation one introduced in the work by Exner and Tater [Phys. Lett. A 382, 283–287 (2018)]. The aim is to provide another illustration of the fact that the asymptotic properties of the latter coupling are determined by the vertex parity by showing that the octahedron graph differs in this respect from the other four for which the edges at high energies effectively disconnect and the spectrum approaches the one of the Dirichlet Laplacian on an interval.