Irreducible representations of crossed products Original Research Article

We prove that if the dimension of any irreducible module for a finite-dimensional algebra over an algebraically closed field divides the dimension of the algebra, then the same is true of any crossed product of that algebra with a group algebra or its dual, provided the characteristic of the field does not divide the order of the group. Kaplanskyʹs Conjecture regarding dimensions of irreducible modules for Hopf algebras then follows for those finite-dimensional semisimple Hopf algebras constructed by a sequence of crossed products involving group algebras and their duals. We show that any semisimple Hopf algebra of prime power dimension in characteristic 0 is of this type, so that Kaplanskyʹs Conjecture holds for these Hopf algebras.