K. Schmüdgen

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math.FA2026

Domain Characterizations of Strong Commutativity\break of Unbounded Self-Adjoint Operators

Konrad Schmüdgen

Let $A$ and $B$ be unbounded self-adjoint operators on a Hilbert space. Suppose that there exists a dense linear subspace $D \subseteq D (A B) \cap D (B A)$ such that $A B x = B A x$ for $x \i…

math.FA2026

The Quaternionic Moment Problem

R. Ben Taher, K. Schmüdgen, E. H. Zerouali

In this paper we develop an approach to the full quaternionic moment problem. We define a hierarchy $H^{k} [q^{*}, q] \subset H^{k + 1} [q^{*}, q]$ , $k\in \mathbb{N}_…

math.FA2026

Antilinar Normal Operators on Hilbert Space

Konrad Schmüdgen

An operator $A$ on a complex Hilbert space $\Hh$ is called antilinear if $A (x + y) = A x + A y$ and $A(λx)=\ovλ Ax$ for $x,y\in \cD(A)$ and $λ\in \dC$. We investigate some classes of dense…

math.FA2024

On the Moment Functionals with Signed Representing Measures

Konrad Schmüdgen

Suppose that $\sA$ is a finitely generated commutative unital real algebra and $K$ is a closed subset of the set $A^$ of characters of $\sA$. We study the following problem: W…