Indexed on: 01 Jun '18Published on: 28 May '18Published in: Reports on Mathematical Physics
Publication date: April 2018 Source:Reports on Mathematical Physics, Volume 81, Issue 2 Author(s): Fedor L. Bakharev, Pavel Exner We investigate spectral properties of the Laplacian in L 2 (Q), where Q is a tubular region in ℝ3 of a fixed cross section, and the boundary conditions combined a Dirichlet and a Neumann part. We analyze two complementary situations, when the tube is bent but not twisted, and secondly, it is twisted but not bent. In the first case we derive sufficient conditions for the presence and absence of the discrete spectrum showing, roughly speaking, that they depend on the direction in which the tube is bent. In the second case we show that a constant twist raises the threshold of the essential spectrum and a local slowndown of it gives rise to isolated eigenvalues. Furthermore, we prove that the spectral threshold moves up also under a sufficiently gentle periodic twist.