Cup Products in Hopf-Cyclic Cohomology
  We construct cup products of two different kinds for Hopf-cyclic cohomology. When the Hopf algebra reduces to the ground field our first cup product reduces to Connes' cup product in ordinary cyclic cohomology. The second cup product generalizes Connes-Moscovici's characteristic map for actions of Hopf algebras on algebras. 
Masoud Khalkhali (Mathematics Department, University of Western   Ontario, London ON, Canada), Bahram Rangipour (Mathematics...