Renormalization Group Improving the Effective Action

TL;DR

This paper explores how renormalization group equations relate to the effective action in quantum and stochastic systems, enabling the inclusion of fluctuations through scale-dependent parameters and improved perturbation theory.

Contribution

It establishes a detailed connection between renormalization group equations and the effective action, allowing for the reconstruction of the effective action from RG equations.

Findings

RG equations can be derived from the effective action.

Effective action can be reconstructed from RG equations using improved perturbation theory.

The approach applies to quantum fluctuations and thermal or statistical fluctuations.

Abstract

The existence of fluctuations together with interactions leads to scale-dependence in the couplings of quantum field theories for the case of quantum fluctuations, and in the couplings of stochastic systems when the fluctuations are of thermal or statistical nature. In both cases the effects of these fluctuations can be accounted for by solutions of the corresponding renormalization group equations. We show how the renormalization group equations are intimately connected with the effective action: given the effective action we can extract the renormalization group equations; given the renormalization group equations the effects of these fluctuations can be included in the classical action by using what is known as improved perturbation theory (wherein the bare parameters appearing in tree-level expressions are replaced by their scale-dependent running forms). The improved action can then be used to reconstruct the effective action, up to finite renormalizations, and gradient terms.