Abstract Non-Hermitian Hamiltonians appearing as operator realizations of-symmetric (-
symmetric in physical literature) zero-range singular perturbations of one-dimensional …

The number of negative squares of all self-adjoint extensions of a simple symmetric operator
of defect one with finitely many negative squares in a Krein space is characterized in terms …

On the spectral theory of singular indefinite Sturm–Liouville operators Page 1 J. Math. Anal.
Appl. 334 (2007) 1439–1449 www.elsevier.com/locate/jmaa On the spectral theory of singular …

Eigenvalues in the essential spectrum of a weighted Sturm-Liouville operator are studied
under the assumption that the weight function has one turning point. An abstract approach to …

We investigate the main spectral properties of quasi--Hermitian extensions of the minimal
symmetric operator $ L_ {\rm min} $ generated by the differential expression $-\frac {{\rm …

We consider quasi-self-adjoint extensions of the symmetric operator A=-(sgn x) d^ 2 dx^ 2,
dom (A)={f ∈ W_2^ 2 (R): f (0)= f'(0)= 0\}, in the Hilbert space L 2 (ℝ). The main result is a …

We consider the indefinite Sturm–Liouville differential expression a (f):=-1 w 1 rf′′, where
a is defined on a finite or infinite open interval I with 0∈ I and the coefficients r and w are …

In a rectangular domain, for the equation of mixed elliptic-hyperbolic type with the Lavrent'ev–
Bitsadze operator and two perpendicular lines of type change, we investigate the first …