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tiny-tim
#9
Feb22-12, 06:02 AM
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Thanks
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hi yicong2011!
Quote Quote by yicong2011 View Post
Or any good reference on it?
you could try Stephen Weinberg's "The Quantum Theory of Fields, Volume I" at page 64

see it free online at http://books.google.co.uk/books?id=h...group%22&hl=en