Yu. M. Arlinskii

Bio: Yu. M. Arlinskii is an academic researcher. The author has contributed to research in topics: Operator space & Semi-elliptic operator. The author has an hindex of 5, co-authored 9 publications receiving 105 citations.

Maximal sectorial extensions and closed forms associated with them

Abstract: We describe all closed sesquilinear forms associated with m-sectorial extensions of a densely defined sectorial operator with vertex at the origin.

On proper accretive extensions of positive linear relations

Abstract: A linear relation S is called a proper extension of a symmetric linear relation S if S ⊂ S ⊂ S*. As is well known, an arbitrary dissipative extension of a symmetric linear relation is proper. In the present paper, we establish criteria for an accretive extension of a given positive symmetric linear relation to be proper.

Theory of operator means

Abstract: New properties of operator connections and means are established. Specifically, representations of an arbitrary connection by means of a concave representing function, an estimate of the norm of a connection in a von Neumann-Schatten ideal, a relation between operator means and convolutions onto operator domains are obtained.

On the class of extremal extensions of a nonnegative operator

Abstract: A nonnegative selfadjoint extension Aof a nonnegative operator A is called extremal if inf {(A)(ϕ) - f),ϕ - f) : ∈ dom A} = 0 for all ϕ ∈ dom A.A new construction of all extremal extensions of a nonnegative densely defined operator will be presented.It employs a fixed auxiliary Hilbert space to factorize each extremal extension.Various functional-analytic interpretations of extremal extensions are studied and some new types of characterizations are obtained.In particular,a purely analytic description of extremal extensions is established,based on a class of functions introduced by M.G.Krein and I.E.Ovearenko.

The von Neumann Problem for Nonnegative Symmetric Operators

Abstract: We develop a new approach and present an independent solution to von Neumann’s problem on the parametrization in explicit form of all nonnegative self-adjoint extensions of a densely defined nonnegative symmetric operator. Our formulas are based on the Friedrichs extension and also provide a description for closed sesquilinear forms associated with nonnegative self-adjoint extensions. All basic results of the well-known Krein and Birman-Vishik theory and its complementations are derived as consequences from our new formulas, including the parametrization (in the framework of von Neumann’s classical formulas) for all canonical resolvents of nonnegative selfadjoint extensions. As an application all nonnegative quantum Hamiltonians corresponding to point-interactions in \(\mathbb{R}^3\) are described.

Componentwise and Cartesian decompositions of linear relations

Abstract: Let $A$ be a, not necessarily closed, linear relation in a Hilbert space $\sH$ with a multivalued part $\mul A$. An operator $B$ in $\sH$ with $\ran B\perp\mul A^{**}$ is said to be an operator part of $A$ when $A=B \hplus (\{0\}\times \mul A)$, where the sum is componentwise (i.e. span of the graphs). This decomposition provides a counterpart and an extension for the notion of closability of (unbounded) operators to the setting of linear relations. Existence and uniqueness criteria for the existence of an operator part are established via the so-called canonical decomposition of $A$. In addition, conditions are developed for the decomposition to be orthogonal (components defined in orthogonal subspaces of the underlying space). Such orthogonal decompositions are shown to be valid for several classes of relations. The relation $A$ is said to have a Cartesian decomposition if $A=U+\I V$, where $U$ and $V$ are symmetric relations and the sum is operatorwise. The connection between a Cartesian decomposition of $A$ and the real and imaginary parts of $A$ is investigated.