Rings whose (proper) cyclic modules have cyclic automorphism-invariant hulls

The object of this article is associate to automorphism-invariant modules that are invariant under any automorphism of their injective hulls with cyclic modules and cyclic modules have cyclic automorphism-invariant hulls. The study of the first sequence allows us to characterize rings whose cyclic right modules are automorphism-invariant and to show that if R is a right Köthe ring, then R is an Artinian principal left ideal ring in case every cyclic right R -module is automorphism-invariant. The study of the second sequence leads us to consider a generalization of hypercyclic rings that are each cyclic R -module has a cyclic automorphism-invariant hull. Such rings are called right a -hypercyclic rings. It is shown that every right a -hypercyclic ring with Krull dimension is right Artinian.