Pavel Exner and Hynek Kovarik
Spectrum of the Schroedinger operator in a perturbed
periodically twisted tube
(27K, LaTeX)

ABSTRACT.  We study Dirichlet Laplacian in a screw-shaped region,
i.e. a straight twisted tube of a non-circular cross section. It
is shown that a local perturbation which consists of "slowing
down" the twisting in the mean gives rise to a non-empty discrete
spectrum.