Condensation of four-particle clusters: a soluble model

The gap type of equation is illustrated for four-particle vertices discussed recently by means of a simple soluble model involving N (where N → infinity) spin-1/2 fermions PSIsub(a)(a = 1,...,N) in 2 + epsilon space-time dimensions with the interaction -(1/2N)g0PSIsup(T)CPSI2 in the limit N → infinity. The model exhibits a condensate of four-particle clusters if the renormalised coupling constant g exceeds some critical value gsub(c). (author)