2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/193808When all Green's functions are known in a given gauge we may raise a question of whether it is possible or not to derive the corresponding ones in a different gauge. The answer is negative in QCD but affirmative in QED provided that we confine ourselves to the covariant gauge characterized by a gauge parameter $α$. We shall discuss the physical significance of this conclusion.20 pages, 4 figuresHigh Energy Physics - Theorytext