  We propose an external field approach to evaluating effective action allowing
the interaction to act everywhere at all times (everlasting). Requiring that
the asymptotic gauge fields are always-interacting, we implement displacement
fields encoding polarization corrections into the derivation of effective
action. The result is a novel polarization summation for one-cut reducible loop
diagrams, which can be applied to two cases: transient quasi-constant
electromagnetic fields, and everlasting interactions. In the first case, a
perturbative expansion of our result recovers the Schwinger-Dyson reducible
diagram series with a Landau pole. The everlasting summation evaluated in
nonperturbative fashion removes the Landau pole, providing a new avenue for
modeling strongly interacting theories.
