Feynman Diagrams
A full lecture reconstruction showing how Lorentz-invariant perturbative QED emerges from the QED path integral as variational calculus on a Gaussian generating functional, and how the surviving terms organize into Feynman diagrams and Feynman rules.
Introduction
The previous lectures built the machinery. This lecture finally turns that machinery into a practical language.
The problem is familiar by now. In Hamiltonian perturbation theory, QED works, but it works in an ugly way. Even something as basic as Compton scattering required a long operator calculation, with several time-ordered intermediate processes that were not Lorent
A full lecture reconstruction showing how bosonic and fermionic coherent-state path integrals combine into the QED generating functional, and how changes of variables turn the Coulomb-gauge Hamiltonian path integral into a manifestly Lorentz-invariant Maxwell–Dirac action with sources.
A full lecture reconstruction showing how loop divergences arise in perturbative QED, why only three classes of divergent loop integrals survive, and how their effects can be absorbed into mass, charge, and field-strength renormalization.