Graded-division algebras and Galois extensions

Abstract

Abstract Graded-division algebras are building blocks in the theory of finite-dimensional associative algebras graded by a group G. If G is abelian, they can be described, using a loop construction, in terms of central simple graded-division algebras. On the other hand, given a finite abelian group G, any central simple G-graded-division algebra over a field F is determined, thanks to a result of Picco and Platzeck, by its class in the (ordinary) Brauer group of F and the isomorphism class of a G-Galois extension of F . This connection is used to classify the simple G-Galois extensions of F in terms of a Galois field extension L / F with Galois group isomorphic to a quotient G / K and an element in the quotient Z 2 ( K , L × ) / B 2 ( K , F × ) subject to certain conditions. Non-simple G-Galois extensions are induced from simple T-Galois extensions for a subgroup T of G. We also classify finite-dimensional G-graded-division algebras and, as an application, finite G-graded-division rings.