Non‐conservation of quasiparticles and bound states

Abstract

An analysis is made of bound states in systems in which the number of quasi‐particlea is not conserved. All calculations are performed using the exact Bose representation of the Pauli operators as well as the Dyson‐Maleev representation, and corrections to the bound state energies with respect to Heitler‐London approximation are found. It is also shown that in this case the approximate second quantization method does not give the correct zero‐order spectrum of the free excitations. Copyright © 1973 WILEY‐VCH Verlag GmbH & Co. KGaA