Steve Clark and Fritz Gesztesy
On Self-adjoint and J-self-adjoint Dirac-type Operators: A Case Study
(135K, LaTeX)

ABSTRACT.  We provide a comparative treatment of some aspects of spectral
theory for self-adjoint and non-self-adjoint (but J-self-adjoint)
Dirac-type operators connected with the defocusing and focusing
nonlinear Schr\"odinger equation, of relevance to nonlinear optics.
In addition to a study of Dirac and Hamiltonian systems, we also
introduce the concept of Weyl-Titchmarsh half-line m-coefficients
(and 2 x 2 matrix-valued M-matrices) in the non-self-adjoint
context and derive some of their basic properties. We conclude with an
illustrative  example showing that crossing spectral arcs in the
non-self-adjoint context imply the blowup of the norm of spectral
projections in the limit where the crossing point is approached.