Exceptional points in Faddeev scattering problem
  Exceptional points are values of the spectral parameter for which the homogeneous Faddeev scattering problem has a non-trivial solution. We study the existence/absence of exceptional points for small perturbations of conductive potentials of arbitrary shape and show that problems with absorbing potentials do not have exceptional points in a neighborhood of the origin. A criterion for existence of exceptional points is given. 
Evgeny Lakshtanov, Boris Vainberg
math-ph math.MP math.SP