Kinetic theory of spatially homogeneous systems with long-range interactions: II. Historic and basic equations

We provide a short historic of the early development of kinetic theory in plasma physics and synthesize the basic kinetic equations describing the evolution of systems with long-range interactions derived in Paper I. We describe the evolution of the system as a whole and the relaxation of a test particle in a bath of field particles at equilibrium or out of equilibrium. We write these equations for an arbitrary long-range potential of interaction in a space of dimension d. We discuss the scaling of the relaxation time with the number of particles for non-singular potentials. For always spatially homogeneous distributions, the relaxation time of the system as a whole scales like N in d > 1 and like N-2 (presumably) or like e(N) (possibly) in d = 1. For always spatially inhomogeneous distributions, the relaxation time of the system as a whole scales like N in any dimension of space. For 1D systems undergoing a dynamical phase transition from a homogeneous to an inhomogeneous phase, we expect a relaxation time of the form N-delta with 1 < delta < 2 intermediate between the two previous cases. The relaxation time of a test particle in a bath always scales like N. We also discuss the kinetic theory of systems with long-range interactions submitted to an external stochastic potential. This paper gathers basic equations that are applied to specific systems in Paper III.