Subtraktionen in Propagatoren und Vertexfunktionen gebundener Teilchen



The purpose of this note is to clarify the arbitrariness of subtraction parameters appearing in the propagator and the vertex function of a composite particle. Although a certain subtraction parameter in the vertex function can be fixed by asymptotic requirements, another arbitrary parameter necessarily remains. This parameter is related to the FREDHOLM character of the integral equation for the one-particle irreducible part of the scattering amplitude. It is shown that only this parameter is connected with the propagator subtraction or the arbitrary vertex pole position, respectively.