Spectral Singularities of a General Point Interaction
  We study the problem of locating spectral singularities of a general complex point interaction with a support at a single point. We also determine the bound states, examine the special cases where the point interaction is P-, T-, and PT-symmetric, and explore the issue of the coalescence of spectral singularities and bound states. 
Ali Mostafazadeh
math-ph math.MP quant-ph