Non-relativistic bound states: the long way back from the Bethe-Salpeter to the Schroedinger equation

TL;DR

This paper reviews the historical development of non-relativistic bound state theories in QED and QCD, tracing the evolution from the Bethe-Salpeter equation to effective field theories, highlighting key conceptual advances.

Contribution

It provides a personal perspective on the progression of bound state theory, emphasizing the transition from complex relativistic equations to simpler effective frameworks.

Findings

Historical insights into bound state theory development

Connection between Bethe-Salpeter and effective field theories

Clarification of conceptual shifts in non-relativistic QFT

Abstract

I review, in a personal perspective, the history of the theory of non-relativistic bound states in QED and QCD from the Bethe-Salpeter equation to the construction of effective field theories.