Multichannel interaction of particles with identical quantum numbers and conditions for particles to be composite

A study is made of the quantum field theory of particles with identical quantum numbers interacting with several channels. The formation of composite particles in such a theory is investigated. Conditions for particles to be composite are derived; these transform some of the elementary particles into composite particles and generalize the well-known conditions $Z_1=0$ and $Z=0$ for the case of a single particle. These conditions are symmetric with respect to all particles. The formalism is generalized to the case when a selfinteraction of the particles is taken into account.