These seem very direct and not ultra advanced, good read.
- Quantum field theory lecture notes | 71, 262, 3
- Quantum field theory bibliography | 130, 2k, 30
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- Particle physics | 137, 32k, 512
- Physics | 276, 47k, 839
- Natural science | 0, 64k, 2k
- Science | 0, 69k, 2k
- Ciro Santilli's Homepage | 262, 238k, 4k
- Klein-Gordon equation | 284, 537, 1