What's your opinion about the book on Quantum Field Theory by Ryder?
It's one of my favored QFT books.
Had never seen such a easily and quickly derivation of the Klein Gordon Equation as he does
It's a very good book. I used it to learn QFT. In parallel I read Bailin&Love, Gauge theories, which uses a path-integral-only approach. It's also very good. Note that this was in a time before there were Peskin&Schroeder (which I don't recommend to the beginner due to the many typos and the few but severe conceptual problems) and before Weinberg's three volumes. Volume 1 just came out a little later, and it was a revelation for me, but I think, I'd have had a hard time to understand it without my study of the more introductory books metioned above.
Nowadays I recommend
M. D. Schwartz, QFT and the Standard Model, Cam. Uni Press (2014)
Always good to know the opinion of a person with so many years working in the field!
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