Orders of Nikshych's Hopf algebra

Juan Cuadra, Ehud Meir

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Let p be an odd prime number and K a number field having a primitive pth root of unity ζp. We prove that Nikshych's non group-theoretical Hopf algebra Hp, which is defined over Q(ζp), admits a Hopf order over the ring of integers OK if and only if there is an ideal I of OK such that I2(p−1)=(p). This condition does not hold in a cyclotomic field. Hence this gives an example of a semisimple Hopf algebra over a number field not admitting a Hopf order over any cyclotomic ring of integers. Moreover, we show that, when a Hopf order over OK exists, it is unique and we describe it explicitly.
Original languageEnglish
Pages (from-to)919-955
Number of pages37
JournalJournal of Noncommutative Geometry
Issue number3
Early online date26 Sep 2017
Publication statusPublished - Sep 2017


  • fusion categories
  • semisimple Hopf algebras
  • Hopf orders
  • group schemes
  • cyclotomic integers


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