• Abstract Bivariant Cuntz Semigroups 

      [OWP-2017-04] Antoine, Ramon; Perera, Francesc; Thiel, Hannes (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] Aron, Richard M.; Falcó, Javier; García, Domingo; Maestre, Manuel (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] Fuller, Adam H.; Hartz, Michael; Lupini, Martino (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] Franz, Uwe; Skalski, Adam; Tomatsu, Reiji (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] Gardella, Eusebio; Lupini, Martino (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] Neufang, Matthias; Salmi, Pekka; Skalski, Adam; Spronk, Nico (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] Curbera, Guillermo P.; Ricker, Werner J. (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] Van Velthoven, Jordy Timo; Voigtlaender, Felix (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] Aron, Richard M.; Bayart, Frédéric; Gauthier, Paul Montpetit; Maestre, Manuel; Nestoridis, Vassili (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] Falcó, Javier; Gauthier, Paul Montpetit; Manolaki, Myrto; Nestoridis, Vassili (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] Nishikawa, Shintaro; Proietti, Valerio (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] Proietti, Valerio; Yamashita, Makoto (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] Klep, Igor; Schweighofer, Markus (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] Schwieger, Kay; Wagner, Stefan (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] Skalski, Adam; Zacharias, Joachim (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] Bondarenko, A. V.; Prymak, A.; Radchenko, D. (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] Conti, Roberto; Hong, Jeong Hee; Szymański, Wojciech (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] Díaz García, Fredy; Krutov, Andrey; Ó Buachalla, Réamonn; Somberg, Petr; Strung, Karen R. (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] Aron, Richard M.; Gauthier, Paul Montpetit; Maestre, Manuel; Nestoridis, Vassili; Falcó, Javier (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] Curbera, Guillermo P.; Ricker, Werner J. (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 ...