Contribution contributed talk
Renormalization of n-particle irreducible effective actions
The n-particle irreducible effective action is a powerful approach to study non-perturbative systems. The method provides a systematic expansion for which the truncation occurs at the level of the action. At the 2PI level one can renormalize using a complicated procedure which involves introducing multiple sets of counterterms, but the method cannot be extended to higher orders. We have developed a method based on a renormalization group approach which allows us to construct a renormalized theory at any order in the nPI approximation. We present results from a calculation using a scalar theory with quartic coupling in 4 dimensions, at the 4 loop level. Both the 2PI and 4PI theories can be renormalized using one bare coupling constant and one bare mass, which are introduced at the level of the Lagrangian.