One-particle irreducibility of Vilkovisky-DeWitt effective action

The effective action formalism introduced by Vilkovisky and later modified by DeWitt is completely covariant suitable for obtaining an effective action that is independent of the parametrization of the quantum fields. Among a few basic properties of an effective action, one property is that it can be written as a sum of one-particle irreducible diagrams. In this work, we verify this property up to three-loop order for Vilkovisky-Dewitt effective action (VDEA) by solving the equations satisfied by VDEA written down in the original parametrization for non-gauge theories.