  We consider a J-self-adjoint 2x2 block operator matrix L in the Feshbach
spectral case, that is, in the case where the spectrum of one main-diagonal
entry is embedded into the absolutely continuous spectrum of the other
main-diagonal entry. We work with the analytic continuation of one of the Schur
complements of L to the unphysical sheets of the spectral parameter plane. We
present the conditions under which the continued Schur complement has operator
roots, in the sense of Markus-Matsaev. The operator roots reproduce (parts of)
the spectrum of the Schur complement, including the resonances. We then discuss
the case where there are no resonances and the associated Riccati equations
have bounded solutions allowing the graph representations for the corresponding
J-orthogonal invariant subspaces of L. The presentation ends with an explicitly
solvable example.
