On Cohen-Macaulay rings of invariants
  We investigate the transfer of the Cohen-Macaulay property from a commutative ring to a subring of invariants under the action of a finite group. Our point of view is ring theoretic and not a priori tailored to a particular type of group action. As an illustration, we briefly discuss the special case of multiplicative actions, that is, actions on group algebras $k[\bbZ^n]$ via an action on $\bbZ^n$. 
Martin Lorenz and Jawahar Pathak