Physics - Quantum Field Theory - Feynman diagrams and perturbative QFT - Feynman Rules and Calculations

4 sections. Section 1 'What Feynman diagrams represent': Each diagram = one term in the perturbation expansion of the S-matrix (scattering amplitude). The amplitude M = sum of all diagrams for a given process. Probability ∝ |M|². Cross-section σ ∝ |M|² × (phase space factor). Tree-level diagrams = l