Projective representations and relative semisimplicity

E. Aljadeff, U. Onn, Y. Ginosar

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Let R be a local (commutative) ring and let p be a prime not invertible in R. Let G be a finite group of order divisible by p. It is well known that the group ring RG admits nonprojective lattices (e.g., R itself with the trivial action). For any element α∈H2(G,R*) one can form the twisted group ring RαG. The "twisting problem" asks whether there exists a class α s.t. the corresponding twisted group ring admits only projective lattices. For fields of characteristic p, the answer is in E. Aljadeff and D. J. S. Robinson [J. Pure Appl. Algebra94 (1994), 1-15]. Here we answer this question for rings of the form Zps, s≥2. The main tools are the classification of modular representation of the Klein 4 group over Z2 and a Chouinard-like theorem [E. Aljadeff and Y. Ginosar, J. Algebra179 (1996), 599-606] for twisted group rings.

Original languageEnglish
Pages (from-to)249-274
Number of pages26
JournalJournal of Algebra
Issue number1
StatePublished - 1 Jul 1999
Externally publishedYes

ASJC Scopus subject areas

  • Algebra and Number Theory


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