On violation of linked-cluster property in the Schwinger model

We examine the violation of linked-cluster property of the Schwinger model in the perturbative series by using partial resummation techniques. An effective chiral-invariant Lagrangian is introduced to study orders higher than the first. It is shown that the linked-cluster property is violated; thus partial resummation technique provides a route to interesting non-perturbative effects. We study also the case of QED with N fermions in 1+1 dimensions and we find that the chiral vacua are a condensate involving necessarily all flavours. © 1994, Società Italiana di Fisica. All rights reserved.