Julian Schwinger 
Particles, Sources, And Fields, Volume 1 [EPUB ebook] 

This classic, the first of three volumes, presents techniques that emphasize the unity of high-energy particle physics with electrodynamics, gravitational theory, and many-particle cooperative phenomena. What emerges is a theory intermediate in position between operator field theory and S-matrix theory, which rejects the dogmas of each and gains thereby a calculational ease and intuitiveness that make it a worthy contender to displace the earlier formulations.