In theoretical physics, a source field is a background field coupled to the original field as
.
This term appears in the action in Richard Feynman's path integral formulation and responsible for the theory interactions. In Julian Schwinger's formulation the source is responsible for creating or destroying (detecting) particles. In a collision reaction a source could be other particles in the collision.[1] Therefore, the source appears in the vacuum amplitude acting from both sides on the Green's function correlator of the theory.
In terms of the statistical and non-relativistic applications, Schwinger's source formulation plays crucial rules in understanding many non-equilibrium systems.[6][7] Source theory is theoretically significant as it needs neither divergence regularizations nor renormalization.[1]
^ abSchwinger, Julian (1998). Particles, sources, and fields. Reading, Mass.: Advanced Book Program, Perseus Books. ISBN0-7382-0053-0. OCLC40544377.