M. Langer and M. Strauss,
Spectral properties of unbounded J-self-adjoint block operator matrices,
J. Spectr. Theory (2017), 137–190
Abstract:
We study the spectrum of unbounded J-self-adjoint block operator matrices.
In particular, we prove enclosures for the spectrum, provide a sufficient
condition for the spectrum being real and derive variational principles
for certain real eigenvalues even in the presence of non-real spectrum.
The latter lead to lower and upper bounds and asymptotic estimates for eigenvalues.