Skew fields not finitely generated as algebras

Abstract

An associative division algebra D is said to be _affine_ over a central subfield k if D is finitely generated as a k-algebra. In 1956 Amitsur famously proved that, when k is uncountable, D cannot be k-affine unless D is algebraic over k. In this paper we consider affineness -- and nonaffineness -- for certain naturally occurring classes of division algebras over arbitrary fields. The primary applications are to division algebras of fractions of suitably conditioned iterated skew polynomial rings over k, including many examples naturally arising in Lie theoretic and quantum group settings. Many transcendental division algebras are thus verified to be nonaffine over k. Division algebras of fractions of Weyl algebras and quantum affine spaces are determined to be affine over their centers exactly when they are finite dimensional over their centers.

Revised. To appear in Contemporary Mathematics, combined proceedings for the workshops "Revisiting Fundamental Problems: Infinite Dimensional Division Algebras -- Algebraicity and Finiteness" and the "Seattle Noncommutative Algebra Conference." Title has been shortened, per referee's recommendation, from the original, "`New' examples of skew fields not finitely generated as algebras."