Fetching the next page so the click feels responsive.
Work through structured problem sets tied directly to the lessons, with hints, hidden solutions, and topic-based navigation.
Operator replacement, commutators, and ladder-operator intuition for free fields.
Weight factors, stationary phase, and the jump from particle paths to field configurations.
Generating functionals, source derivatives, and how perturbative diagrams emerge.
Tree versus loop structure, ultraviolet sensitivity, and bare-to-measured parameters.