Correlation functions of local composite operators from generalized unitarity

We describe the use of generalized unitarity for the construction of correlation functions of local gauge-invariant operators in general quantum field theories and illustrate this method with several calculations in N = 4 super-Yang-Mills theory involving BPS and non-BPS operators. Form factors of gauge-invariant operators and their multi-operator generalization play an important role in our construction. We discuss various symmetries of the momentum space presentation of correlation functions, which is natural in this framework and give examples involving non-BPS and any number of BPS operators. We also discuss the calculation of correlators describing the energy flow in scattering processes as well as the construction of the effective action of a background gravitational field.