The Derivative Expansion at Small Mass for the Spinor Effective Action

We study the small mass limit of the one-loop spinor effective action, comparing the derivative expansion approximation with exact numerical results that are obtained from an extension to spinor theories of the partial-wave-cutoff method. In this approach one can compute numerically the renormalized one-loop effective action, for radially separable gauge field background fields in spinor QED. We highlight an important difference between the small mass limit of the derivative expansion approximation for spinor and scalar theories.