30 citations · 93 across the 17 of their papers we have counts for
21 papers
Domain Characterizations of Strong Commutativity\break of Unbounded Self-Adjoint Operators
Konrad Schmüdgen
Let and be unbounded self-adjoint operators on a Hilbert space. Suppose that there exists a dense linear subspace such that for $x \i…
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 , $k\in \mathbb{N}_…
Antilinar Normal Operators on Hilbert Space
Konrad Schmüdgen
An operator on a complex Hilbert space $\Hh$ is called antilinear if and $A(λx)=\ovλ Ax$ for $x,y\in \cD(A)$ and $λ\in \dC$. We investigate some classes of dense…
On the Moment Functionals with Signed Representing Measures
Konrad Schmüdgen
Suppose that $\sA$ is a finitely generated commutative unital real algebra and is a closed subset of the set of characters of $\sA$. We study the following problem: W…
On the Matricial Truncated Moment Problem. II
Conrad Mädler, Konrad Schmüdgen
We continue the study of truncated matrix-valued moment problems begun in arXiv:2310.00957. Let . Suppose that is a measurable space an…
On the Truncated Matricial Moment Problem. I
Conrad Mädler, Konrad Schmüdgen
This paper is about the general truncated matrix-valued moment problem. Let denote the complex Hermitian -matrices, . Suppose that $(\ma…
Positivstellensätze for Semirings
Konrad Schmüdgen, Matthias Schötz
In this paper we develop a number of results and notions concerning Positivstellensätze for semirings (preprimes) of commutative unital real algebras. First we reduce the Archimede…
The multidimensional truncated Moment Problem: Carathéodory Numbers
Philipp J. di Dio, Konrad Schmüdgen
Let be a finite-dimensional subspace of , where is a locally compact Hausdorff space, and a ba…
The multidimensional truncated Moment Problem: Atoms, Determinacy, and Core Variety
Philipp J. di Dio, Konrad Schmüdgen
This paper is about the moment problem on a finite-dimensional vector space of continuous functions. We investigate the structure of the convex cone of moment functionals (supporti…
Unbounded Operators on Hilbert -Modules
René Gebhardt, Konrad Schmüdgen
Let and be Hilbert -modules over a -algebra $\CAlg{A}$. New classes of (possibly unbounded) operators are introduced and investigated. Instead of the d…
Flat extensions in *-algebras
Bernard Mourrain, Konrad Schmüdgen
The main result of the paper is a flat extension theorem for positive linear functionals on *-algebras. The theorem is applied to truncated moment problems on cylinder sets, on mat…
On -normal operators and quantum complex plane
Jaka Cimpric, Yurii Savchuk, Konrad Schmüdgen
For let $\cA$ denote the unital -algebra with generator and defining relation . Based on this algebra we study -normal operators, the complex $…
Positivstellensätze for Algebras of Matrices
Yurii Savchuk, Konrad Schmüdgen
The paper is concerned with various types of noncommutative Positivstellensätze for the matrix algebra $M_n(\cA)$, where $\cA$ is an algebra of operators acting on a unitary space,…
A noncommutative version of the Fejér-Riesz theorem
Yurii Savchuk, Konrad Schmüdgen
Let $\cX$ be the unital *-algebra generated by the unilateral shift operator. It is shown that for any nonnegative operator $X\in \cX$ there is an element $Y\in \cX$ such that $X=Y…
Unbounded Induced Representations of *-Algebras
Yu. Savchuk, K. Schmuedgen
Induced representations of -algebras by unbounded operators in Hilbert space are investigated. Conditional expectations of a -algebra $\cA$ onto a unital -subalge…
Commutator Representations of Covariant Differential Calculi on Quantum Groups
Konrad Schmuedgen
Let (G,d) be a first order differential *-calculus on a *-algebra A. We say that a pair (π,F) of a *-representation πof A on a dense domain D of a Hilbert space and a symmetric ope…
Commutator Representations of Differential Calculi on the Quantum Group SU_q(2)
Konrad Schmuedgen
Let (Γ,d) be the 3D-calculus or the 4D_{\pm}-calculus on the quantum group SU_q(2). We describe all pairs (π, F) of a *-representation πof O(SU_q(2)) and of a symmetric operator F…
Operator Representations of a q-Deformed Heisenberg Algebra
Konrad Schmuedgen
A class of well-behaved *-representations of a q-deformed Heisenberg algebra is studied and classified.
On the Construction of Covariant Differential Calculi on Quantum Homogeneous Spaces
Konrad Schmuedgen
Let A be a coquasitriangular Hopf algebra and X the subalgebra of A generated by a row of a matrix corepresentation u or by a row of u and a row of the contragredient representatio…
Classification of Bicovariant Differential Calculi on the Quantum Groups and
I. Heckenberger, K. Schmuedgen
For transcendental values of all bicovariant first order differential calculi on the coordinate Hopf algebras of the quantum groups and are classified. I…
Levi-Civita Connections on the Quantum Groups SL_{q}(N), O_{q}(N) and Sp_{q}(N)
I. Heckenberger, K. Schmuedgen
For bicovariant differential calculi on quantum groups various notions on connections and metrics (bicovariant connections, invariant metrics, the compatibility of a connection wit…