Exact renormalization group and Phi-derivable approximations

Abstract

We show that the so-called Phi-derivable approximations can be combined with the exact renormalization group to provide efficient non-perturbative approximation schemes. On the one hand, the Phi-derivable approximations allow for a simple truncation of the infinite hierarchy of the renormalization group flow equations. On the other hand, the flow equations turn the non linear equations that derive from the Phi-derivable approximations into an initial value problem, offering new practical ways to solve these equations.