We investigate Schrödinger operators with δ-and δ′-interactions supported on
hypersurfaces, which separate the Euclidean space into finitely many bounded and …

We systematically develop Weyl-Titchmarsh theory for singular differential operators on
arbitrary intervals $(a, b)\subseteq\mathbb {R} $ associated with rather general differential …

We review recent developments in the theory of 1-D Schrödinger operators with local point
interactions on a discrete set. The progress in this area was stimulated by recent advances …

We investigate quantum graphs with infinitely many vertices and edges without the common
restriction on the geometry of the underlying metric graph that there is a positive lower …

We investigate spectral properties of Gesztesy–Šeba realizations DX, α and DX, β of the 1-D
Dirac differential expression D with point interactions on a discrete set [Formula: see text] …

1 Elliptic operators, Dirichlet-to-Neumann maps and quasi boundary triples Page 1 1 Elliptic
operators, Dirichlet-to-Neumann maps and quasi boundary triples Jussi Behrndt and Matthias …

The core results of the Kreı̆n-Višik-Birman theory of self-adjoint extensions of semi-
bounded symmetric operators are reproduced, both in their original and in a more modern …

We study the Hamiltonians HX, α, q with δ-type point interactions at the centers xk on the
positive half line in terms of energy forms. We establish analogs of some classical results on …

Consider the minimal Sturm–Liouville operator A= Amin generated by the differential
expression in the Hilbert space L2 (R+, H) where T= T⁎⩾ 0 in H. We investigate the …

We investigate the bottom of the spectra of infinite quantum graphs, ie, Laplace operators on
metric graphs having infinitely many edges and vertices. We introduce a new definition of …