Simplicity of twisted C*-algebras of higher-rank graphs and crossed products by quasifree actions

@article{Kumjian2014SimplicityOT,
  title={Simplicity of twisted C*-algebras of higher-rank graphs and crossed products by quasifree actions},
  author={Alex Kumjian and David Pask and Aidan Sims},
  journal={arXiv: Operator Algebras},
  year={2014}
}
We characterise simplicity of twisted C*-algebras of row-finite k-graphs with no sources. We show that each 2-cocycle on a cofinal k-graph determines a canonical second-cohomology class for the periodicity group of the graph. The groupoid of the k-graph then acts on the cartesian product of the infinite-path space of the graph with the dual group of the centre of any bicharacter representing this second-cohomology class. The twisted k-graph algebra is simple if and only if this action is… 

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