How do you read the QED, QCD and standard model Lagrangians? What do all the symbols and tensors represent? And, how can you derive them by yourselves?

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    $\begingroup$ QFT textbook will explain the meaning of the symbols and tensors. It is not really a derivation to find these Lagragnians. It is postulated by educated guess and experimental evidence (e.g. parity non-conservation) $\endgroup$ – user26143 Nov 17 '13 at 7:31
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    $\begingroup$ @DIMension10 I would like to regard writing the interaction terms by gauge invariance as an educated guess $\endgroup$ – user26143 Nov 17 '13 at 15:21
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    $\begingroup$ There is an answer at physicsoverflow.org/5191 $\endgroup$ – Arnold Neumaier Jul 11 '15 at 7:35