New answers tagged effective-action
A n-particle reducible diagram is a diagram that can be cut into two pieces if one cuts n or less lines. Conversely, a n-particle irreducible (n-PI) diagram cannot be cut into two pieces if one cuts n lines. The sunset diagram is 3-particle reducible, since it has 3 internal lines, but it is both 1-PI and 2-PI, and contributes to the self-energy (which ...
There is an extensive, survey-like introduction by Juergen Berges, dating from 2004. For the renormalization of 2PI effective actions see also a very recent paper by Carrington et al..
Top 50 recent answers are included