Rings that are Morita equivalent to their opposites

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We consider the following problem: Under what assumptions are one or more of the following equivalent for a ring R: (A) R is Morita equivalent to a ring with involution, (B) R is Morita equivalent to a ring with an anti-automorphism, (C) R is Morita equivalent to its opposite ring. The problem is motivated by a theorem of Saltman which roughly states that all conditions are equivalent for Azumaya algebras. Based on the recent general bilinear forms of [10], we present a general machinery to attack the problem, and use it to show that (C) (B) when R is semilocal or Q-finite. Further results of similar flavor are also obtained, for example: If R is a semilocal ring such that MR(n) has an involution, then MR(2) has an involution, and under further mild assumptions, R itself has an involution. In contrast to that, we demonstrate that (B) (A). Our methods also give a new perspective on the Knus-Parimala-Srinivas proof of Saltman's Theorem. Finally, we give a method to test Azumaya algebras of exponent 2 for the existence of involutions, and use it to construct explicit examples of such algebras.

Original languageEnglish
Pages (from-to)26-61
Number of pages36
JournalJournal of Algebra
StatePublished - 5 May 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015 Elsevier Inc..


  • Anti-automorphism
  • Azumaya algebra
  • Bilinear form
  • Brauer group
  • Corestriction
  • General bilinear form
  • Involution
  • Morita equivalence
  • Semilocal ring

ASJC Scopus subject areas

  • Algebra and Number Theory


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