Examples of embedded eigenvalues for the Dirichlet Laplacian in perturbed waveguides
Karl J. Witsch · Mathematical Methods in the Applied Sciences · 1990
Abstract It is shown that there exist domains Ω ⊂ ℝN, which outside of some ball coincide with the strip ℝN − 1 × (0, π) and for which the Dirichlet Laplacian – Δ has eigenvalues within the subinterval (1, 4) of the essential spectrum (1, ∞).