Effective-Action Expansion in Perturbation Theory

I present a systematic method for the development of the effective-action expansion in perturbation theory. The multiderivative terms beyond the effective potential can be evaluated in a direct and simple manner relying only on the familiar momentum space and Feynman propagator. I have used the self-coupled scalar field to explain the details of this new formulation. The effective-action expansion for this model in the one-loop approximation is evaluated up to the terms containing four derivatives. This method can be readily generalized to other models with spins and internal symmetries.