The Renormalization Group and Singular Perturbations: Multiple-Scales, Boundary Layers and Reductive Perturbation Theory

TL;DR

This paper develops a unified renormalization group method for asymptotic analysis of differential equations with multiple scales and boundary layers, offering advantages over traditional approaches.

Contribution

It introduces a renormalization group framework that simplifies asymptotic analysis without ad hoc assumptions, applicable to boundary layers and bifurcation problems.

Findings

Provides approximate solutions superior to conventional methods

Eliminates need for asymptotic matching

Derives amplitude equations and center manifolds

Abstract

Perturbative renormalization group theory is developed as a unified tool for global asymptotic analysis. With numerous examples, we illustrate its application to ordinary differential equation problems involving multiple scales, boundary layers with technically difficult asymptotic matching, and WKB analysis. In contrast to conventional methods, the renormalization group approach requires neither {\it ad hoc\/} assumptions about the structure of perturbation series nor the use of asymptotic matching. Our renormalization group approach provides approximate solutions which are practically superior to those obtained conventionally, although the latter can be reproduced, if desired, by appropriate expansion of the renormalization group approximant. We show that the renormalization group equation may be interpreted as an amplitude equation, and from this point of view develop reductive perturbation theory for partial differential equations describing spatially-extended systems near bifurcation points, deriving both amplitude equations and the center manifold.