Three- and four-body systems with the Functional Renormalization Group

Abstract

The Efimov effect arises in three-body systems near the unitary limit. Some of its features are universal, while others are not. This article uses a Functional-Renormalization- Group approach to discuss the Efimov effect and four-body systems. In this context, the Efimov effect appears as a consequence of the Renormalization-Group flow of couplings. On the four- body system, we find three tetramers below each Efimov trimer, and no evidence of four- body universality breaking. Two of these tetramers are in agreement with quantum-mechanical calculations and experimental results.