Clifford theory for group-graded rings. II.
The aim of this paper is to present a starting point for proving existence of injective minimal models (cf. [8]) for some systems of complete differential graded algebras.
In this paper we introduce a new class of differential graded algebras named DG -algebras and present Lie operations on this kind of algebras. We give two examples: the algebra of forms and the algebra of noncommutative differential forms of a -algebra. Then we introduce linear connections on a -bimodule over a -algebra and extend these connections to the space of forms from to . We apply these notions to the quantum hyperplane.
Using derived categories, we develop an alternative approach to defining Koszulness for positively graded algebras where the degree zero part is not necessarily semisimple.
Let be a group with identity and let be a -graded ring. In this paper, we introduce and study the concept of graded -ideals of . A proper graded ideal of is called a graded -ideal of if whenever where , then either or or . We introduce several results concerning --ideals. For example, we give a characterization of graded -ideals and their homogeneous components. Also, the relations between graded -ideals and others that already exist, namely, the graded prime ideals,...
We investigate gradings on tame blocks of group algebras whose defect groups are dihedral. For this subfamily of tame blocks we classify gradings up to graded Morita equivalence, we transfer gradings via derived equivalences, and we check the existence, positivity and tightness of gradings. We classify gradings by computing the group of outer automorphisms that fix the isomorphism classes of simple modules.