Quantum gravity with higher derivative terms

A renormalizable (but perturbatively nonunitary) model of quantum gravity is considered which includes quadratic terms in the curvature tensors. One-loop counterterms are calculated for this enlarged action by using the background field method in the context of the dimensional regularization scheme and the renormalization group equations are derived. Finally the possibility is discussed that the Weyl ghosts which are characteristic of this model and would in principle expoil unitarity do not actually occur. A difficulty with the cosmological term is pointed out