- #1
muppet
- 608
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Currents and the "quantum" effective action
Hi all,
I've been reading Burgess' Primer on effective field theory: arXiv:hep-th/0701053v2. I can't follow the reasoning here:
I could maybe begin to make sense of this if I were allowed to assume that −(δ[itex]\Gamma[/itex]/δϕ) is the sum of 1PI irreducible graphs with one external line, so that using bubble graphs as "sources" leads to a cancellation of 1 particle reducible diagrams (although in this case it would still be far from obvious to me that this cancellation still works when you have more than two external sources). But as this is what we're puporting to show here, I can't follow the logic at all. Any comments would be greatly appreciated.
Hi all,
I've been reading Burgess' Primer on effective field theory: arXiv:hep-th/0701053v2. I can't follow the reasoning here:
W[J] [is] the sum of all connected graphs that are constructed using vertices and propagators built from the classical lagrangian, L, and having the currents, J, as external lines. But [itex]\Gamma[/itex][ϕ] just differs from W[J] by subtracting [itex]\int[/itex]d4x Jϕ, and evaluating the result at the specific configuration J[ϕ] = −(δ[itex]\Gamma[/itex]/δϕ). This merely lops off all of the 1-particle reducible graphs, ensuring that [itex]\Gamma[/itex][ϕ] is given by summing 1-particle irreducible graphs.
I could maybe begin to make sense of this if I were allowed to assume that −(δ[itex]\Gamma[/itex]/δϕ) is the sum of 1PI irreducible graphs with one external line, so that using bubble graphs as "sources" leads to a cancellation of 1 particle reducible diagrams (although in this case it would still be far from obvious to me that this cancellation still works when you have more than two external sources). But as this is what we're puporting to show here, I can't follow the logic at all. Any comments would be greatly appreciated.