The Classical Sine Gordon Theory

Abstract

The organizing committee of this school had invited Ludwig Fadeev as one of the lecturers for the tutorials. Unfortunately, Fadeev was prevented from coming. Thus I was asked to step into his place. I do not know the programme which Fadeev had planned to follow. Since in the seminars by M. Lüscher, A. Luther, and A. Neveu the quantum sine Gordon theory (or, equivalently, the massive Thirring model) will play a central rôle, I finally decided to give an introduction to the classical sine Gordon theory. The classical theory instructs us about the elementary excitations of which the system is capable. Moreover, it provides a variety of explicit analytic results used in the WKB approximation for the mass spectrum of the corresponding quantum theory.