1. Riccardo D’Auria, Mario Trigiante, From Special Relativity to Feynman Diagrams, A Course in Theoretical Particle Physics for Beginners (Springer, Belin, 2016); Alexander L. Fetter, John Dirk Walecka, Quantum Theory of Many-Particle Systems (Dover, NY, 2003); Richard D. Mattuck, A Guide to Feynman Diagrams in the Many-Body Problem (Dover, NY, 1992); A. Zee, Quantum Field Theory in a Nutshell, Second Edition (Amazon Books,2010)
2. A. Plastino, M.C. Rocca, J. of Phys. Comm. 2, 115029 (2018)
3. C.G. Bollini, J.J. Giambiagi, Phys. Lett. B 40, 566 (1972a)
4. C.G. Bollini, J.J. Giambiagi, Il Nuovo Cim. B 12, 20 (1972b)
5. C. G. Bollini and J.J Giambiagi , Phys. Rev. D 53, 5761 (1996)