# A Effective field theory in Srednicki's book

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1. Feb 22, 2017

### brushguy

Hi!

I'm currently learning for my QFT exam with the book from srednicki (here as pdf: http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf) and I am trying to understand the chapter "Effective field theory" (p. 185 in the pdf above)

He first introduces an ultraviolet cutoff Λ and then computes the path integral over all fields with momentum above Λ.
Then he defines the "Wilsonian effective action" and writes down the corresponding lagrangian
( (29.11) on p. 186 ).

-) How can one derive eq (29.11) (the lagrangian density of the Wilsonian effective action) ?

-) Why can one compute the new coefficients m2(Λ) \alpha, λ(Λ), ... the way it is shown in eq (29.13) - (29.23) ?
I am not confused about how exactly the computation works, but with how he comes up with the ansatz itself. For example, why the new mass m(Λ) can be computed with eq (29.20)