Statistical mechanics of composite particles

This paper is concerned with the Statistical Mechanics of an hydrogenic plasma with randomly fixed ions. Starting from the “physical” problem we introduce an “ideal” problem (with an enlarged state space); the latter is defined in such a way that its dynamical evolution leads to the dynamical evolution of the former by means of a projection technique. The interesting features of the “ideal” problem are to be simpler than the “physical” one (usual commutation relations for the “ideal” creation and annihilation operators) and to have a two-particle hamiltonian (instead of an infinite number of particle-operators as in all previous works).