Quasiparticles and the quantum fluctuations of local observables

Abstract

The role that quasiparticles play in a strong interaction system with spontaneous symmetry breaking is examined. We find, using a non- perturbative cluster decomposition method, that the quasiparticles do not saturate the physical local observables at small distances. The fermion number density serves as a clearcut example. A component due to localized random quantum fluctuations of the order parameter(s) in the vacuum state and the contributions of ``quasiparticles'' corresponding to other local minima of the effective potential is needed. At large distances, the ordinary quasiparticle picture emerges in the response of the system to classical background fields but the above mentioned component acts as a source for them.