Analyticity properties and many-particle structure in general quantum field theory

In the framework of L.S.Z. field theory in the case of a single massive scalar field, the two-particle irreducible parts of then-point functions (in any single channel and for arbitraryn) are defined as the solutions of a system of integral equations suggested by the perturbative framework. These solutions enjoy the analytic and algebraic properties of generaln-point functions (up to possible polar singularities of generalized C.D.D. type). Morever it is shown that the completeness of asymptotic states in the two-particle spectral region is equivalent to the analyticity of the two-particle irreduciblen-point functions in the corresponding regions of complex momentum space.