Spectral Triples on ON

  • Magnus GoffengEmail author
  • Bram Mesland
Part of the MATRIX Book Series book series (MXBS, volume 1)


We give a construction of an odd spectral triple on the Cuntz algebra O N , whose K-homology class generates the odd K-homology group K1(O N ). Using a metric measure space structure on the Cuntz-Renault groupoid, we introduce a singular integral operator which is the formal analogue of the logarithm of the Laplacian on a Riemannian manifold. Assembling this operator with the infinitesimal generator of the gauge action on O N yields a θ-summable spectral triple whose phase is finitely summable. The relation to previous constructions of Fredholm modules and spectral triples on O N is discussed.


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We thank the MATRIX for the program Refining C-algebraic invariants for dynamics using KK-theory in Creswick, Australia (2016) where this work came into being. We are grateful to the support from Leibniz University Hannover where this work was initiated. We also thank Francesca Arici, Robin Deeley, Adam Rennie and Alexander Usachev for fruitful discussions and helpful comments, and the anonymous referee for a careful reading of the manuscript. The first author was supported by the Swedish Research Council Grant 2015-00137 and Marie Sklodowska Curie Actions, Cofund, Project INCA 600398.


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Authors and Affiliations

  1. 1.Department of Mathematical SciencesChalmers University of Technology and the University of GothenburgGothenburgSweden
  2. 2.Institut für AnalysisLeibniz Universität HannoverHannoverGermany

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