Loop diagrams, ultraviolet divergences, bare versus measured parameters, and running couplings.
Renormalization explains how loop corrections modify naive parameters and why measured quantities depend on scale. It packages ultraviolet sensitivity into a consistent procedure that makes predictive QFT possible.
This page is tuned to searches about what renormalization is, where divergences come from, and how running couplings arise from loop momentum.
A full lecture reconstruction introducing perturbative quantum electrodynamics from the Coulomb-gauge Hamiltonian, identifying the fine-structure constant as the small expansion parameter, and using time-independent perturbation theory to analyze the QED vacuum and one-electron states.
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.