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    • On the Computational Content of the Theory of Borel Equivalence Relations 

      [OWP-2021-06] Bazhenov, Nikolay; Monin, Benoit; San Mauro, Luca; Zamora, Rafael (Mathematisches Forschungsinstitut Oberwolfach, 2021-03-17)
      This preprint offers computational insights into the theory of Borel equivalence relations. Specifically, we classify equivalence relations on the Cantor space up to computable reductions, i.e., reductions induced by Turing ...
    • The Elser Nuclei Sum Revisited 

      [OWP-2021-05] Grinberg, Darij (Mathematisches Forschungsinstitut Oberwolfach, 2021-03-16)
      Fix a finite undirected graph $\Gamma$ and a vertex $v$ of $\Gamma$. Let $E$ be the set of edges of $\Gamma$. We call a subset $F$ of $E$ \textit{pandemic} if each edge of $\Gamma$ has at least one endpoint that can be ...
    • The C-Map as a Functor on Certain Variations of Hodge Structure 

      [OWP-2021-04] Mantegazza, Mauro; Saha, Arpan (Mathematisches Forschungsinstitut Oberwolfach, 2021-03-15)
      We give a new manifestly natural presentation of the supergravity c-map. We achieve this by giving a more explicit description of the correspondence between projective special Kähler manifolds and variations of Hodge ...
    • Amorphic Complexity of Group Actions with Applications to Quasicrystals 

      [OWP-2021-03] Fuhrmann, Gabriel; Gröger, Maik; Jäger, Tobias; Kwietniak, Dominik (Mathematisches Forschungsinstitut Oberwolfach, 2021-02-02)
      In this article, we define amorphic complexity for actions of locally compact $\sigma$-compact amenable groups on compact metric spaces. Amorphic complexity, originally introduced for $\mathbb Z$-actions, is a topological ...
    • 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 ...
    • Boundary Conditions for Scalar Curvature 

      [OWP-2021-01] Bär, Christian; Hanke, Bernhard (Mathematisches Forschungsinstitut Oberwolfach, 2021-01-04)
      Based on the Atiyah-Patodi-Singer index formula, we construct an obstruction to positive scalar curvature metrics with mean convex boundaries on spin manifolds of infinite $K$-area. We also characterize the extremal case. ...