The standard Feynman rules used for perturbative calculations in quantum chromodynamics (QCD) and quantum electrodynamics (QED) are derived from a Lagrangian that is first-order in derivatives. It includes a three-point vertex which obscures the precise disentangled manner in which spin and momentum are interchanged during the interactions. An unambiguous understanding of this interchange is insightful for efficiently extracting physically relevant information from various Green’s functions. To separate the scalar and spin degrees of freedom and gain physical insight from the outset, we examine the quark-gluon and electron-photon vertex using the less commonly employed second-order formalism of QCD and QED.

victor.banda@upslp.edu.mx

Victor Miguel Banda Guzman