8 citations · 13 across the 9 of their papers we have counts for
11 papers
Extensions of positive symmetric operators and Krein's uniqueness criteria
Zoltán Sebestyén, Zsigmond Tarcsay
We revise Krein's extension theory of positive symmetric operators. Our approach using factorization through an auxiliary Hilbert space has several advantages: it can be applied to…
Canonical graph contractions of linear relations on Hilbert spaces
Zsigmond Tarcsay, Zoltán Sebestyén
Given a closed linear relation between two Hilbert spaces and , the corresponding first and second coordinate projections and are both line…
Range-kernel characterizations of operators which are adjoint of each other
Zoltán Sebestyén, Zsigmond Tarcsay
We provide necessary and sufficient conditions for a pair of Hilbert space operators in order that they satisfy and . As a main result we establish an improvem…
Lebesgue type decompositions for linear relations and Ando's uniqueness criterion
Seppo Hassi, Zoltán Sebestyén, Henk de Snoo
A linear relation, i.e., a multivalued operator from a Hilbert space to a Hilbert space has Lebesgue type decompositions , where…
A characterization of positive normal functionals on the full operator algebra
Zoltán Sebestyén, Zsigmond Tarcsay, Tamás Titkos
Using the recent theory of Krein--von Neumann extensions for positive functionals we present several simple criteria to decide whether a given positive functional on the full opera…
Adjoint of sums and products of operators in Hilbert spaces
Zoltán Sebestyén, Zsigmond Tarcsay
We provide sufficient and necessary conditions guaranteeing equations and concerning densely defined unbounded operators between Hilbert spa…
On the uniqueness of the Lebesgue decomposition of normal states on
Zoltán Sebestyén, Zsigmond Tarcsay, Tamás Titkos
The non-commutative theory of the Lebesgue-type decomposition of positive functionals is originated with S. P. Gudder. Although H. Kosaki's counterexample shows that the decomposit…
On the sum between a closable operator and a -bounded operator
Dan Popovici, Zoltán Sebestyén, Zsigmond Tarcsay
We provide several perturbation theorems regarding closable operators on a real or complex Hilbert space. In particular we extend some classical results due to Hess--Kato, Kato--Re…
Extensions of positive operators and functionals
Zoltán Sebestyén, Zsolt Szűcs, Zsigmond Tarcsay
We consider linear operators defined on a subspace of a complex Banach space into its topological antidual acting positively in a natural sense. The goal of this paper is to invest…
A Short-type Decomposition Of Forms
Zoltán Sebestyén, Zsigmond Tarcsay, Tamás Titkos
The main purpose of this paper is to present a decomposition theorem for nonnegative sesquilinear forms. The key notion is the short of a form to a linear subspace. This is a gener…
Operators having selfadjoint squares
Zoltán Sebestyén, Zsigmond Tarcsay
The main goal of this paper is to show that a (not necessarily densely defined or closed) symmetric operator acting on a real or complex Hilbert space is selfadjoint exactly wh…