Exotic coactions

Steven Kaliszewski, Magnus B. Landstad, John Quigg

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


If a locally compact group G acts on a C∗-algebra B, we have both full and reduced crossed products and each has a coaction of G. We investigate 'exotic' coactions in between the two, which are determined by certain ideals E of the Fourier-Stieltjes algebra B(G); an approach that is inspired by recent work of Brown and Guentner on new C∗-group algebra completions. We actually carry out the bulk of our investigation in the general context of coactions on a C∗-algebra A. Buss and Echterhoff have shown that not every coaction comes from one of these ideals, but nevertheless the ideals do generate a wide array of exotic coactions. Coactions determined by these ideals E satisfy a certain 'E-crossed product duality', intermediate between full and reduced duality. We give partial results concerning exotic coactions with the ultimate goal being a classification of which coactions are determined by ideals of B(G).

Original languageEnglish (US)
Pages (from-to)411-434
Number of pages24
JournalProceedings of the Edinburgh Mathematical Society
Issue number2
StatePublished - May 1 2016


  • C∗-bialgebra
  • Fourier-Stieltjes algebra
  • coaction
  • group C∗-algebra

ASJC Scopus subject areas

  • Mathematics(all)


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