# Wilsonian effective field theory

1. May 31, 2010

### LAHLH

Hi,

could anyone explain to me why in effective field theory (as in ch29 srednicki), you look at diagrams with only $$k<\Lambda$$ as external lines and $$k>\Lambda$$ for your interal lines? why do these diagrams with say, 6 external legs of this type, equate to the constant $$c_6$$ say? In previous chapters of the book it's usually the exact 6 point vertex function that would equate to such a diagram, not the 6 point coupling constant itself etc.

I understand the math behind what Srednicki is doing, but not sure I understand what he is actually trying to do here, so all comments on this whole topic in QFT would be great.

thanks

2. May 31, 2010

### ansgar

I second that! :-)

3. Jun 2, 2010

### LAHLH

Hah, anyone out there know how this stuff works?