2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/143734In this note, we determine the ground state energy of the translation invariant Pauli-Fierz model to subleading order $O(α^3)$ with respect to powers of the finestructure constant $α$, and prove rigorous error bounds of order $O(α^{4})$. A main objective of our argument is its brevity.AMS Latex, 8 pagesMathematical PhysicsSpectral Theory81Q10text