ABSTRACT
This chapter discusses perturbation theory by deriving the functional component which generates the S-matrix elements of the theory. It evaluates the Fourier transforms of the Green functions by using the Feynman rules and develops a perturbative expansion of the opi Green functions. The chapter shows that the connected Green functions all have a propagator factor associated with each external line, and the same is clearly true of the full Green functions. It also presents the calculation of the scattering cross section of particles in a scalar field.
