Exponent Reduction for Radical Abelian Algebras,

Let k be a field. A radical abelian algebra over k is a crossed product (K/k, α), where K = k(T) is a radical abelian extension of k, T is a subgroup of K* which is finite modulo k*, and α H2(G, K*) is represented by a cocycle with values in T. The main result is that if A is a radical abelian algebra over k, and m = exp(A kk(μ)), where μ denotes the group of all roots of unity, then k contains the mth roots of unity. Applications are given to projective Schur division algebras and projective Schur algebras of nilpotent type.