J. Behrndt, M. Langer and V. Lotoreichik,
Spectral estimates for resolvent differences of self-adjoint elliptic operators,
Integral Equations Operator Theory 77 (2013), 1–37
Abstract:
The concept of quasi boundary triples and Weyl functions from extension theory of
symmetric operators in Hilbert spaces is developed further and spectral estimates
for resolvent differences of two self-adjoint extensions in terms of general operator ideals are proved.
The abstract results are applied to self-adjoint realizations of second order elliptic
differential operators on bounded and exterior domains, and partial differential operators
with δ-potentials supported on hypersurfaces are studied.