If Z[J] is the generating functional for the path-integral, could any prove (or more reasonably, refer me to a proof) that W[J]≡ℏilog(Z[J])
So far I've only seen theory-dependent "examples" (basically showing how in ϕ4 theory the two-point function from W gives only connected contributions).
I'm looking for a generic systematic proof for a general field theory.
Answer
The logarithmic relationship is equivalent to Z[J]=exp[iW[J]]
The combinatorial factor will work, too. Recall that when we evaluate Feynman diagrams, we have to divide by the symmetry factor. The symmetry group of a disconnected, n-component diagram includes the permutation group of all the n components if the components are the same, that's why there is 1/n! in front of a "fixed single 1-component diagram" to the n-th power.
The extra symmetry group from permuting the components is reduced to the product of ni! over all subgroups of the group of n components that contain the same diagram. But ∏i1ni!
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