Olaf Post
Eigenvalues in Spectral Gaps of a Perturbed Periodic Manifold
(172K, LaTeX2e with 3 PS-Figures (30 pages))

ABSTRACT.  We consider a non-compact Riemannian periodic manifold such that the corresponding Laplacian has a spectral gap. By continuously perturbing the periodic metric locally we can prove the existence of eigenvalues in a gap. A lower bound on the number of eigenvalue branches crossing a fixed level is established in terms of a discrete eigenvalue problem. Furthermore, we discuss examples of perturbations leading to infinitely many eigenvalue branches coming from above resp. finitely many branches coming from below.