Starting from the earlier notions of stationary action principles, these tutorial notes shows how Schwinger's Quantum Action Principle descended from Dirac's formulation, which independently led Feynman to his path-integral formulation of quantum mechanics. Part I brings out in more detail the connection between the two formulations, and applications are discussed. Then, the Keldysh-Schwinger time-cycle method of extracting matrix elements is described. Part II will discuss the variational formulation of quantum electrodynamics and the development of source theory.

Includes supplementary material: sn.pub/extras

Autorentext
Professor Kimball Milton is the George Lynn Cross Research Professor of Physics at the University of Oklahoma. Kim Milton, a student of Julian Schwinger, studies in particular vacuum energy phenomena (the Casimir effect) in contexts ranging from cosmological through hadronic to condensed matter systems. He is the author, together with J Mehra of "Climbing the Mountain: The Scientific Biography of Julian Schwinger" Oxford University Press, 2000.

Inhalt
Historical introduction.- Review of classical action principles.- Classical field theory - electrodynamics.- Quantum Action Principle.- Time-cycle or Schwinger-keldysh Formulation.- Relativistic Theory of Fields.- Nonrelativistic Source theory.- Concluding remarks.