
Let \(F\) be a field and \(D\) a central division \(F\)-algebra of degree \(n\). A subgroup \(G\) of the multiplicative group \(D^*\) of \(D\) is said to be irreducible, if \(F[G]=D\). Under the hypothesis that \(n=p^r\), where \(p\) is prime and \(r\) is a positive integer, the paper under review gives several criteria for \(D\) to be a crossed product. The authors show that \(D\) has this property if and only if \(D^*\) possesses an irreducible solvable subgroup. They prove that \(D\) is a crossed product, in case \(D^*\) has an irreducible finite subgroup. When \(p>2\) or \(\text{char}(F)=0\), it is established that \(D\) is such a product if and only if \(D^*\) contains an irreducible subgroup satisfying a group identity. The proof of the third result relies on the Tits alternative, namely the fact that a finitely generated linear group contains a noncyclic free subgroup, unless it is solvable-by-finite (see [\textit{J. Tits}, J. Algebra 20, 250-270 (1972; Zbl 0236.20032)]).
irreducible subgroups, Units, groups of units (associative rings and algebras), crossed products, Algebra and Number Theory, group identities, central division algebras, Twisted and skew group rings, crossed products, Tits alternative, Finite-dimensional division rings, Linear algebraic groups over arbitrary fields
irreducible subgroups, Units, groups of units (associative rings and algebras), crossed products, Algebra and Number Theory, group identities, central division algebras, Twisted and skew group rings, crossed products, Tits alternative, Finite-dimensional division rings, Linear algebraic groups over arbitrary fields
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