Browsing 1 - Oberwolfach Preprints (OWP) by MSC "46"
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Abstract Bivariant Cuntz Semigroups
[OWP-2017-04] (Mathematisches Forschungsinstitut Oberwolfach, 2017-02-13)We show that abstract Cuntz semigroups form a closed symmetric monoidal category. Thus, given Cuntz semigroups $S$ and $T$, there is another Cuntz semigroup $((S,T))$ playing the role of morphisms from $S$ to $T$. Applied ... -
Analytic Structure in Fibers
[OWP-2016-13] (Mathematisches Forschungsinstitut Oberwolfach, 2016-08-17)Let $B_X$ be the open unit ball of a complex Banach space $X$, and let $\mathcal{H}^\infty(B_X)$ and $\mathcal{A}_u(B_X)$ be, respectively, the algebra of bounded holomorphic functions on $B_X$ and the subalgebra of uniformly ... -
Boundary Representations of Operator Spaces, and Compact Rectangular Matrix Convex Sets
[OWP-2016-24] (Mathematisches Forschungsinstitut Oberwolfach, 2016-12-13)We initiate the study of matrix convexity for operator spaces. We define the notion of compact rectangular matrix convex set, and prove the natural analogs of the Krein-Milman and the bipolar theorems in this context. We ... -
Classification of idempotent states on the compact quantum groups Uq(2), SUq(2) and SOq(3)
[OWP-2009-08] (Mathematisches Forschungsinstitut Oberwolfach, 2009-03-02)We give a simple characterisation of those idempotent states on compact quantum groups which arise as Haar states on quantum subgroups, show that all idempotent states on quantum groups $U_q(2)$, $SU_q(2)$, and $SO_q(3) ... -
Cocycle Superrigidity and Group Actions on Stably Finite C*-Algebras
[OWP-2017-01] (Mathematisches Forschungsinstitut Oberwolfach, 2017-01-17)Let $\Lambda $ be a countably infinite property (T) group, and let $D$ be UHF-algebra of infinite type. We prove that there exists a continuum of pairwise non (weakly) cocycle conjugate, strongly outer actions of $\Lambda ... -
Contractive Idempotents on Locally Compact Quantum Groups
[OWP-2012-19] (Mathematisches Forschungsinstitut Oberwolfach, 2012)A general form of contractive idempotent functionals on coamenable locally compact quantum groups is obtained, generalising the result of Greenleaf on contractive measures on locally compact groups. The image of a convolution ... -
Convolution in Dual Cesàro Sequence Spaces
[OWP-2022-20] (Mathematisches Forschungsinstitut Oberwolfach, 2022-12-16)We investigate convolution operators in the sequence spaces $d_p$, for 1 $\leqslant p<\infty$. These spaces, for $p$ > 1, arise as dual spaces of the Cesàro sequence spaces $ces_p$ thoroughly investigated by G. Bennett. A ... -
Coorbit Spaces and Dual Molecules: the Quasi-Banach Case
[OWP-2022-08] (Mathematisches Forschungsinstitut Oberwolfach, 2022-05-27)This paper provides a self-contained exposition of coorbit spaces associated with integrable group representations and quasi-Banach function spaces. It extends the theory in [Studia Math., 180(3):237–253, 2007] to locally ... -
Dirichlet Approximation and Universal Dirichlet
[OWP-2016-12] (Mathematisches Forschungsinstitut Oberwolfach, 2016-08-16)We characterize the uniform limits of Dirichlet polynomials on a right half plane. We extend the approximation theorems of Runge, Mergelyan and Vitushkin to the Dirichlet setting with respect to the Euclidean distance and ... -
A Function Algebra Providing New Mergelyan Type Theorems in Several Complex Variables
[OWP-2019-02] (Mathematisches Forschungsinstitut Oberwolfach, 2019-02-11)For compact sets $K\subset \mathbb C^{d}$, we introduce a subalgebra $A_{D}(K)$ of $A(K)$, which allows us to obtain Mergelyan type theorems for products of planar compact sets as well as for graphs of functions. -
Groups with Spanier-Whitehead Duality
[OWP-2019-23] (Mathematisches Forschungsinstitut Oberwolfach, 2019-09-17)We introduce the notion of Spanier-Whitehead $K$-duality for a discrete group $G$, defined as duality in the KK-category between two $C*$-algebras which are naturally attached to the group, namely the reduced group ... -
Homology and $K$-Theory of Torsion-Free Ample Groupoids and Smale Spaces
[OWP-2020-20] (Mathematisches Forschungsinstitut Oberwolfach, 2020-10-09)Given an ample groupoid, we construct a spectral sequence with groupoid homology with integer coefficients on the second sheet, converging to the $K$-groups of the groupoid C*-algebra when the groupoid has torsion-free ... -
Infeasibility certificates for linear matrix inequalities
[OWP-2011-28] (Mathematisches Forschungsinstitut Oberwolfach, 2011-05-25)Farkas' lemma is a fundamental result from linear programming providing linear certi cates for infeasibility of systems of linear inequalities. In semidefinite programming, such linear certificates only exist for strongly ... -
Lifting Spectral Triples to Noncommutative Principal Bundles
[OWP-2021-02] (Mathematisches Forschungsinstitut Oberwolfach, 2021-01-11)Given a free action of a compact Lie group $G$ on a unital C*-algebra $\mathcal{A}$ and a spectral triple on the corresponding fixed point algebra $\mathcal{A}^G$, we present a systematic and in-depth construction of ... -
Noncommutative topological entropy of endomorphismus of Cuntz Algebras
[OWP-2008-12] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-16)Noncommutative topological entropy estimates are obtained for ‘finite range’ endomorphisms of Cuntz algebras,generalising known results for the canonical shift endomorphisms. Exact values are computed for a class of ... -
On Concentrators and Related Approximation Constants
[OWP-2013-14] (Mathematisches Forschungsinstitut Oberwolfach, 2013-06-10)Pippenger ([Pip77]) showed the existence of (6m, 4m, 3m, 6)-concentrator for each positive integer m using a probabilistic method. We generalize his approach and prove existence of (6m, 4m, 3m, 5.05)-concentrator (which ... -
On conjugacy of MASAs and the outer automorphism group of the Cuntz algebra
[OWP-2013-21] (Mathematisches Forschungsinstitut Oberwolfach, 2013-10-29)We investigate the structure of the outer automorphism group of the Cuntz algebra and the closely related problem of conjugacy of MASAa in $\mathcal{O}_n$. In particular, we exhibit an uncountable family of MASAs, conjugate ... -
Positive Line Bundles Over the Irreducible Quantum Flag Manifolds
[OWP-2020-01] (Mathematisches Forschungsinstitut Oberwolfach, 2020-02-03)Noncommutative Kähler structures were recently introduced by the third author as a framework for studying noncommutative Kähler geometry on quantum homogeneous spaces. It was subsequently observed that the notion of a ... -
Rational Approximation on Products of Planar Domains
[OWP-2016-05] (Mathematisches Forschungsinstitut Oberwolfach, 2016-06-17)We consider $A(\Omega)$, the Banach space of functions $f$ from $ \overline{\Omega}=\prod_{i \in I} \overline{U_i}$ to $\mathbb{C}$ that are continuous with respect to the product topology and separately holomorphic, where ... -
Solid extensions of the Cesàro operator on the Hardy space H2(D)
[OWP-2013-11] (Mathematisches Forschungsinstitut Oberwolfach, 2013-04-23)We introduce and study the largest Banach space of analytic functions on the unit disc which is solid for the coefficient-wise order and to which the classical Ces`aro operator $\mathcal{C}:H^2 \to H^2$ can be continuously ...