Additive and multiplicative renormalization of topological charge with   improved gluon/fermion actions: A test case for 3-loop vacuum calculations,   using overlap or clover fermions
  We calculate perturbative renormalization properties of the topological charge, using the standard lattice discretization given by a product of twisted plaquettes. We use the overlap and clover action for fermions, and the Symanzik improved gluon action for 4- and 6-link loops.   We compute the multiplicative renormalization of the topological charge density to one loop; this involves only the gluon part of the action. The power divergent additive renormalization of the topological susceptibility is calculated to 3 loops.   Our work serves also as a test case of the techniques and limitations of lattice perturbation theory, it being the first 3-loop computation in the literature involving overlap fermions. 
A. Skouroupathis and H. Panagopoulos (Department of Physics,   University of Cyprus, Nicosia)